The Australian redback spider (Latrodectus hasselti) is one of the widow spiders (Latrodectus), a cosmopolitan group of small, round-bodied spiders.
Female redback spiders are black (occasionally brownish) with an obvious orange to red longitudinal stripe on the upper abdomen, with the red stripe sometimes being broken, and an hourglass-shaped red/orange spot on the underside of the abdomen. Females are about a centimeter long, but males are just a few mm. The males' red markings are often less distinct. The male's body is light brown with white markings on the upper side of the abdomen and a pale hourglass marking on the underside. Juveniles have additional white markings on the abdomen (http://australianmuseum.net.au/Redback-Spider, accessed 24 December 2009)
Redback spiders are native to all areas of Australia. Redbacks are also found in New Zealand (North and South islands), having been introduced through grape importation from Australia. Records of the spiders’ appearance span most of Southeast Asia, including as far north as India. This species has also recently been sighted in south central Japan.
Biogeographic Regions: oriental (Introduced ); australian (Native ); oceanic islands (Introduced )
- Garb, J., A. Gonzalez, R. Gillespie. 2004. The black widow spider genus Latrodectus (Araneae : Theridiidae): phylogeny, biogeography, and invasion history. Molecular Phylogenetics and Evolution, 31: 1127-1142. Accessed February 01, 2012 at http://apps.webofknowledge.com.proxy.lib.umich.edu/full_record.do?product=UA&search_mode=GeneralSearch&qid=44&SID=4E2hGGMoCJCm7E7eOKD&page=1&doc=1.
- Nihei, N., M. Yoshida, M. Kobayashi, H. Kaneta, R. Shimamura, N. Agui. 2003. Geographic information systems (GIS) analysis of the distribution of the redback spider Latrodectus hasseltii (Araneae: Theridiadae) in Osaka, Japan. Medical Entomology and Zoology, 54: 177-186. Accessed February 01, 2012 at http://apps.webofknowledge.com.proxy.lib.umich.edu/full_record.do?product=UA&search_mode=GeneralSearch&qid=18&SID=4E2hGGMoCJCm7E7eOKD&page=1&doc=1.
- Vink, C., J. Derraik, C. Phillips, P. Sirvid. 2010. The invasive Australian redback spider, Latrodectus hasseltii Thorell 1870 (Araneae: Theridiidae): current and potential distributions, and likely impacts. Biological Invasions, 13: 1003-1019.
- Vink, C., P. Sirvid, J. Malumbres-Olarte, J. Griffiths, P. Paquin, A. Paterson. 2008. Species status and conservation issues of New Zealand's endemic Latrodectus spider species (Araneae : Theridiidae). Invertebrate Systematics, 22: 589-604. Accessed February 01, 2012 at http://apps.webofknowledge.com.proxy.lib.umich.edu/full_record.do?product=UA&search_mode=GeneralSearch&qid=3&SID=4E2hGGMoCJCm7E7eOKD&page=1&doc=1.
Although its native range is presumed to be Australia, Latrodectus hasselti has been inadvertently introduced to New Zealand, Japan, Southeast Asia, and possibly elsewhere (Garb et al. 2004 and references therein).
Redback spiders are bilaterally symmetrical, cold-blooded spiders belonging to the family Theridiidae. Their closest relative is the North American southern black widow spider (Latrodectus mactans), which is distinguishable from redback spiders by the absence of a red dorsal stripe. Female redbacks average 10 mm in length, with body sizes as large as a pea, and are significantly larger than males (which average 3-4 mm). Females are typically black with a red stripe, sometimes broken, on the dorsal surface of the upper abdomen (crossing parallel to the length of the body), and a red hourglass-shaped spot on the ventral side of the abdomen. Young female redbacks have additional white markings on their abdomens that they lose as adults. Male redbacks are typically light brown in color with a dorsal red stripe and a paler hourglass shape on the ventral side of the abdomen, both of which are similar to, but less distinct than, female markings. Males also retain the white markings on the upper side of the abdomen through adulthood. Each sex has slender legs and is venomous.
Range length: 3 to 10 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; venomous
Sexual Dimorphism: female larger; sexes colored or patterned differently; female more colorful
- Australian Museum, 2011. "ANIMAL SPECIES: Redback Spider, Latrodectus hasselti" (On-line). Australian Museum. Accessed February 13, 2012 at http://australianmuseum.net.au/Redback-Spider/.
Redback spiders are most commonly found in urban areas, preferring the shelter human habitats provide from unfavorable weather. They inhabit urban and suburban areas within all of Australia's terrestrial biomes, preferring tropical and temperate areas. They are less common in savanna, chaparral and desert areas and are not found at the continent's highest elevations. The appearance of redbacks in Japan shows that they are also capable of surviving at very low temperatures (-3 degrees C).
Range elevation: 0 (low) m.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; rainforest
Other Habitat Features: urban ; suburban
- Isbister, G., M. Gray. 2003. Latrodectism: a prospective cohort study of bites by formally identified redback spiders. Medical Journal of Australia, 179: 88-91. Accessed February 01, 2012 at http://www.mja.com.au/public/issues/179_02_210703/isb10807_fm.html.
Redback spiders are insectivores that prey on small insects caught within their webs such as ants (Formicidae spp). They also sometimes catch larger animals stuck in their webs such as mice, small birds, snakes, small lizards, king crickets, Cromwell chafer beetles, and trapdoor spiders. Redback spiders also steal stored prey caught in the webs of other spiders. All redbacks have a potentially venomous bite, however only females have been known to envenomate prey.
Redback spiders catch their prey in a unique way. At night, females construct a complex web system reaching in all directions, including towards the ground. They set traps for prey by bringing a strand of their silk web down and sticking it to the ground surface. Next, they climb up that line, adding an additional silk line on top of the original to strengthen it. They then pull the line taut and a single trap is complete. They do this multiple times creating a number of traps and wait for prey to run or fly into a line and get stuck. Redbacks eventually wrap up each prey item, storing some for later meals.
Animal Foods: birds; mammals; reptiles; insects; terrestrial non-insect arthropods
Foraging Behavior: stores or caches food
Primary Diet: carnivore (Insectivore )
- Queensland Museum, 2007. "Redback Spider Latrodectus hasseltii, family Theridiidae" (On-line). Queensland Museum. Accessed February 13, 2012 at http://www.qm.qld.gov.au/Find+out+about/Animals+of+Queensland/Spiders/Modern+Spiders+Infraorder+Araneomorphae/Redback+and+Brown+Widow+spiders/Redback+Spider.
The primary ecosystem role of this species is as an insect predator. They can have a negative impact on some arthropod communities as a predator and by displacing other species. Redback spiders were a factor in the endangerment of Cromwell chafer beetles (Prodontria lewisii). They are also prey for a small number of species, including daddy longlegs (Pholcus phalangioides) and white-tailed spiders (Lampona spp). There is evidence that their egg sacs are a target for Philolema latrodecti and Ichneuman wasps (Ichneumonidae).
Ecosystem Impact: creates habitat
- Ichneumonidae (Order Hymenoptera, Class Insecta)
- Philolema latrodecti (Order Hymenoptera, Class Insecta)
- Bibbs, C., L. Buss. 2011. "Widow spider parasitoids" (On-line). Accessed September 06, 2012 at http://entnemdept.ufl.edu/creatures/beneficial/wasps/latrodectus_parasitoids.htm.
- Krogmann, L., A. Austin. 2011. Systematics of Australian Agenioideus Ashmead (Hymenoptera: Pompilidae) with the ﬁrst record of a spider wasp parasitizing Latrodectus hasselti Thorell (redback spider). Australian Journal of Entymology, doi:10.1111/j.1440-6055.2011.00850.x: 1-9. Accessed September 08, 2012 at http://naturkundemuseum-bw.academia.edu/LarsKrogmann/Papers/1534005/Systematics_of_Australian_Agenioideus_Ashmead_Hymenoptera_Pompilidae_with_the_first_record_of_a_spider_wasp_parasitizing_Latrodectus_hasselti_Thorell_redback_spider_.
Redback spiders are aposematic; their red markings warn predators of their venomous nature. Unsurprisingly then, few species prey on redbacks; only daddy longlegs and white-tailed spiders have been seen to repeatedly catch and kill redbacks. There is also evidence that their eggs are preyed on by Mantisflies (Mantisipidae).
- Daddy longlegs spider (Pholcus phalangioides)
- White-tailed spider (Lampona cylindrata)
- White-tailed spider (Lampona murina)
- Mantisipidae (Order Neuroptera, Class Insecta)
Anti-predator Adaptations: aposematic
Life History and Behavior
Webs are constructed so that spiders are able to sense vibrations, using their hair-like setae, made by animals running into the web's strands. Unmated female redbacks deposit a chemical pheromone on their webs to attract males and, during courtship, male redbacks must make their presence known using tactile cues to avoid being consumed. As with most spiders, redbacks have simple eyes that are capable of sensing movement.
Communication Channels: visual ; tactile ; chemical
Other Communication Modes: pheromones ; vibrations
Perception Channels: visual ; tactile ; vibrations ; chemical
- Jerhot, E., J. Stolz, M. Andrade, S. Schulz. 2010. Acylated Serine Derivatives: A Unique Class of Arthropod Pheromones of the Australian Redback Spider, Latrodectus hasselti. Angewandte Chemie - International Edition, 49/11: 2037-2040.
Latrodectus hasselti is well known for its sexual cannibalism. Females often consume males during copulation following the stereotyped self-sacrifice ‘‘somersault’’ behavior performed by the male (Forster 1992; Andrade and Banta 2002). After insertion of one of his copulatory organs (palps), the male turns a somersault through 180 degrees so that his abdomen comes to rest against the female's mouthparts, whereupon she may begin to devour him (Forster 1992). The cannibalistic process is slow and males may use their two palps to copulate sequentially with a single female--inseminating one of her two independent sperm storage organs with each palp--then sacrifice themselves to their cannibalistic mates. This extreme strategy increases paternity for the mating in question, but also results in the male's death, eliminating the possibility of copulating with additional females (Andrade 1996; Andrade and Banta 2002). Andrade et al. (2005) documented a novel male trait—an abdominal constriction that appears during courtship—that allows a male to survive partial cannibalism from the first copulation and go on to mate with a female a second time. Inseminating both of the female's sperm storage organs by copulating with her twice dramatically increases the male's paternity share in the event the female proceeds to mate with additional males. This constriction allows males to overcome the potential fitness limit imposed by their own suicidal strategy by prolonging survival across two cannibalistic copulations.
A female may mate sequentially with different males and under some circumstances may choose to reduce the paternity share of one of the males by consuming him sooner rather than later (Stoltz et al. 2009).
As is true for other Latrodectus, during Latrodectus hasselti copulation, a discrete portion of the male's copulatory organ (the apical sclerite) breaks off and remains in the female's reproductive tract (Andrade 1996; Snow et al. 2006). This broken off apical sclerite reduces sperm competition from other males subsequently mating with the same female by acting as a "sperm plug", physically blocking access to the female's sperm storage organ (Snow et al. 2006).
Young redback spiders follow a similar developmental sequence to other spider species. A week and a half after females lay their egg sacs, the first molt occurs inside individual eggs. The first instar (stage between molts) follows, during which spiderlings hatch and disperse within 14 days, usually via wind currents. Young spiders look like small adults. Members of this species reach maturity and adult size after 4 instars/5 molts (males) or 6 instars/7 molts (females).
- Commonwealth Scientific and Industrial Research Organization (CSIRO). 2012. "Redback spider" (On-line). Commonwealth Scientific and Industrial Research Organization (CSIRO). Accessed September 08, 2012 at http://www.csiro.au/Outcomes/Environment/Biodiversity/Redback-Spiders.aspx.
- Downes, M. 1987. Postembryonic Development of Latrodectus hasselti Thorell (Araneae, Theridiidae). Journal of Arachnology, 14: 293-301.
- Hickman, C., L. Roberts, S. Keen, A. Larson, D. Eisenhour. 2007. Animal Diversity - Fifth Edition. New York, New York: McGraw-Hill.
Female Redback spiders live for 2-3 years whereas males only live for about 6-7 months. Male lifespan is limited by sexual cannibalism during mating, male-male competition, and size differential between males and females (often leading to females killing the much smaller males).
The presence of Redback spider populations in Japan shows that they are capable of surviving without food for long periods of time, as they likely traveled the long distance from Australia to Japan in cargo carried by ships with little to no food available. Juveniles may survive up to 160 days and adults 300 days without food. At later stages of starvation they are sluggish and incapable of finding food for themselves, however Redbacks are noted to recover immediately after one meal.
Status: wild: 6 to 36 months.
- Forster, L., J. Kavale. 1989. Effects of food deprivation on Latrodectus hasselti Thorell (Araneae: Theridiidae), the Australian redback spider. New Zealand Journal of Zoology, 16: 401-408.
Redback spiders can mate anytime during the year but do so most commonly during summer months when temperatures are higher. Redback spiders are polyandrous (males typically mate once while females often have multiple mates). This species' mating behavior includes sexual cannibalism. Smaller males attempt to mate multiple times with a single, much larger, female. When they approach a female, a male will insert one pedipalp into one of the female's sperm-storage organs. During this action it will twist its body 180 degrees, placing its abdomen directly near the female's fangs (a "copulatory somersault"). Early in this first sperm transfer, the female begins to masticate her partner; most males (69.6-83.3%), are able to break free of this first restraint. After additional courtship behaviors by males, the mating behavior described is repeated, with the male's second pedipalp inserted into the female's other sperm-storage organ. Following 65% of these second insertions, the female will completely consume the male.
Some male redbacks have adapted a unique behavior called "mid-dorsal abdominal constriction" in order to increase survival after the first attempt of female cannibalism. This involves manually shrinking their abdomens and, in so doing, shifting essential organs anteriorly, lengthening survival time of males so they may inseminate the female’s second sperm-storage organ. Those who succeed at this behavior increase chances of paternity.
Due to cannibalistic behaviors by females, a majority of male redbacks only mate with one female. During the mating period, several males are typically found on a female's web, leading males to compete with one another, often fatally, for access to females. Redbacks have a lengthy courtship period of around 3 hours; however, males may rush these activities if another male is detected approaching. If they attempt to shorten courtship too much, females typically cannibalize males before copulation is completed. During copulation, the apical sclerite of the male redback spider's copulatory organ may break off and act as a plug in the female's sperm-storage organs, blocking insemination by other males and helping increase chances of paternity for the first mate. Cannibalized males who exhibit this behavior potentially more than double their likelihood of paternity compared to males not consumed. After consumption of a male, females are much less receptive to further mates. Because 80% of males never find a mate, it is important to invest everything into their one mating experience. Redback spider males who survive copulation are likely sterile for the rest of their lives.
Mating System: polyandrous
Redback spiders in Australia can breed at any time of year, but breeding is most common during summer months. After females have mated, they may use internally stored sperm for up to 2 years to fertilize their eggs. During this time they lay multiple batches of eggs, from different supplies of sperm, with a period of at least 1-3 weeks between each batch. Batches are made up of about 10 egg sacs, each of which contains approximately 250 eggs, which are laid and suspended in the web. When sacs are laid they are white but after time turn brown. The length of time before hatching is related to temperature. It has been recorded that they emerge after 17-24 days at 30°C and after 26-43 days at 25°C. The average duration of egg to spiderling emergence is 28.7 days. Below 25°C, development is typically arrested. Once emerged, sexual organs start soon begin developing, with female redback spiders reaching sexual maturity after 120 days and the males after 90 days.
Breeding interval: Redback spiders are capable of breeding once every 1-3 weeks.
Breeding season: Year round (most common during summer months)
Average number of offspring: 2500.
Range gestation period: 17 to 43 days.
Average gestation period: 28.7 days.
Average age at sexual or reproductive maturity (female): 120 days.
Average age at sexual or reproductive maturity (male): 90 days.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous ; sperm-storing ; delayed fertilization
Information on parental investment for this species is limited. Females lay large numbers of eggs and suspend them in bundles from their webs, possibly as a form of protection. When hatched, spiderlings quickly disperse from their mother's territory. Because male redbacks typically do not survive past mating, it is assumed that no male parental investment occurs.
Parental Investment: female parental care ; pre-hatching/birth (Protecting: Female)
- Andrade, M., E. Banta. 2002. Value of male remating and functional sterility in redback spiders. Animal Behaviour, 63: 857-870. Accessed February 01, 2012 at http://apps.webofknowledge.com.proxy.lib.umich.edu/full_record.do?product=UA&search_mode=GeneralSearch&qid=36&SID=4E2hGGMoCJCm7E7eOKD&page=1&doc=1.
- Andrade, M., L. Gu, J. Stoltz. 2005. Novel male trait prolongs survival in suicidal mating. Biology Letters, 1: 276-279. Accessed February 01, 2012 at http://apps.webofknowledge.com.proxy.lib.umich.edu/full_record.do?product=UA&search_mode=GeneralSearch&qid=39&SID=4E2hGGMoCJCm7E7eOKD&page=1&doc=1.
- Australian Museum, 2011. "ANIMAL SPECIES: Redback Spider, Latrodectus hasselti" (On-line). Australian Museum. Accessed February 13, 2012 at http://australianmuseum.net.au/Redback-Spider/.
- Downes, M. 1987. Postembryonic Development of Latrodectus hasselti Thorell (Araneae, Theridiidae). Journal of Arachnology, 14: 293-301.
- Snow, L., A. Abdel-Mesih, M. Andrade. 2006. Broken Copulatory Organs are Low-Cost Adaptations to Sperm Competition in Redback Spiders. Ethology, 4: 379-389. Accessed February 01, 2012 at http://apps.webofknowledge.com.proxy.lib.umich.edu/full_record.do?product=UA&search_mode=GeneralSearch&qid=47&SID=4E2hGGMoCJCm7E7eOKD&page=1&doc=1.
- Stoltz, J., D. Elias, C. Andrade. 2008. Females Reward Courtship by Competing Males in a Cannibalistic Spider. Behavioral Ecology and Sociobiology, 62: 689-697. Accessed February 01, 2012 at http://apps.webofknowledge.com.proxy.lib.umich.edu/full_record.do?product=UA&search_mode=GeneralSearch&qid=1&SID=4E2hGGMoCJCm7E7eOKD&page=1&doc=1.
- Vink, C., J. Derraik, C. Phillips, P. Sirvid. 2010. The invasive Australian redback spider, Latrodectus hasseltii Thorell 1870 (Araneae: Theridiidae): current and potential distributions, and likely impacts. Biological Invasions, 13: 1003-1019.
Evolution and Systematics
Systematics and Taxonomy
The phylogeny and biogeography of the genus Latrodectus have been reviewed by Garb et al. (2004).
The New Zealand endemic Latrodectus katipo appears to be the closest extant relative to L. hasselti (Garb et al. 2004).
Molecular Biology and Genetics
Statistics of barcoding coverage: Latrodectus hasselti
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
Barcode data: Latrodectus hasseltii
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Latrodectus hasseltii
Public Records: 7
Specimens with Barcodes: 7
Species With Barcodes: 1
Redback spiders do not currently have any special conservation status.
Latrodectus hasselti has been expanding its range for many years via inadvertent introductions to new regions by human activity and its conservation status is not a concern. However, its introduced range now includes New Zealand and there is some concern that this species could threaten the endemic New Zealand widow spider L. katipo via asymmetric hybridization and genetic swamping (Garb et al. 2004 and references therein).
Relevance to Humans and Ecosystems
Redback spiders are one of the most dangerous spiders in Australia. When disturbed, larger females often bite and envenomate intruders. Bites typically occur during the summer season and in the late afternoon when temperatures are highest and the spiders are most active. The venom is produced in the cephalothorax and is delivered via the animal's fangs. Redback spiders can control the amount of venom that they inject and "dry" bites are not unheard of. The main toxic component of the venom, α-latrotoxin, affects humans differently depending on the amount injected. Males are believed to be as capable of delivering painful, venomous bites as females, although bites are rarely reported. Approximately 80% of bites cause little to no effect. Of the remaining 20%, most feel pain radiating from the bite spot for only about 24 hours. More serious cases include pain lasting longer than 24 hours, bumps and swollen lymph nodes followed by sweating, a rapid heart beat, possible vomiting, headache, and insomnia. Unlike most other envenomation syndromes, the effects of bites from this species may persist for several days, weeks, or months. Fatalities from redback bites are rare and none have occurred since 1956, when an antivenom was created. Most bites from this species can be treated with household remedies (ice packs and pain relievers). Bites that show more severe symptoms may require antivenom to be administered intramuscularly, sometimes in multiple injections. Recently, Australian doctors have chosen to only give the antivenom when absolutely necessary because they fear possible negative side effects. Other doctors are not convinced of its effectiveness in general.
Negative Impacts: injures humans (bites or stings, venomous )
- Isbister, G. 2002. Failure of intramuscular antivenom in Red-back spider envenoming. Emergency Medicine, 14: 436-439. Accessed February 01, 2012 at http://apps.webofknowledge.com.proxy.lib.umich.edu/full_record.do?product=UA&search_mode=GeneralSearch&qid=58&SID=4E2hGGMoCJCm7E7eOKD&page=1&doc=2.
- Nimorakiotakis, B., K. Winkel. 2004. Spider bite--the redback spider and its relatives. Australian family physician, 33: 153-157. Accessed February 01, 2012 at http://www.racgp.org.au/scriptcontent/search/searchracgpresults.cfm?section=search&cx=000337812831128799297%3Acwnpztvg-0a&cof=FORID%3A11&searchterm=Spider+bite%3A+the+redback+spider+and+its+relatives&sa=Search.
- Wiener, S. 2003. Latrodectism: a prospective cohort study of bites by formally identified redback spiders. Medical Journal of Australia, 179: 455. Accessed February 01, 2012 at http://www.mja.com.au/cgi-bin/s.cgi?q=Latrodectism%3A+a+prospective+cohort+study+of+bites+by+formally+identified+redback+spiders&cmd=Search%21.
While redback spiders are predators of terrestrial insects, they do not appear to affect insect populations enough to have any positive effects on humans.
Latrodectus hasselti is among the most medically significant spiders in the world. Humans are bitten far more often by females than by the smaller males. The bite often causes severe pain and other symptoms lasting for days (Isbister and Gray 2003). A variety of Latrodectus widow spider species are found around the world and their bites tend to produce similar symptoms. Bites are often followed by the gradual onset of severe, unremitting local, regional, and systemic symptoms. These may include pain at the bite site or in the whole of the bitten limb, intense sweating, piloerection ("goosebumps"), and muscle fasciculations (twitching). Symptoms may become severe and generalized and include hypertension (elevated blood pressure), tachycardia (abnormally rapid heartbeat), nausea, vomiting, and abdominal pain. Although death is extremely uncommon, patients may be left with serious symptoms for days or weeks if left untreated (Graudins et al. 2001). There is an effective antivenom treatment for L. hasselti bites and several studies have found this antivenom to be effective in treating bites from other Latrodectus species as well (Gaudins et al. 2001). According to Wiener (2003), there have been no deaths from L. hasselti bites since antivenom became available in 1956.
The redback spider (Latrodectus hasseltii) is a species of venomous spider indigenous to Australia. It is a member of the cosmopolitan genus Latrodectus, the widow spiders. The adult female is easily recognised by her spherical black body with a prominent red stripe on the upper side of her abdomen and an hourglass-shaped red/orange streak on the underside. Females have a body length of about 10 millimetres (0.4 in), while the male is much smaller, being only 3–4 mm (0.12–0.16 in) long.
Mainly nocturnal, the female redback lives in an untidy web in a warm sheltered location, commonly near or inside human residences. It preys on insects, spiders and small vertebrates that become ensnared in its web. It kills its prey by injecting a complex venom through its two fangs when it bites, before wrapping them in silk and sucking out the liquefied insides. Male spiders and spiderlings often live on the periphery of the female spiders' web and steal leftovers. Other species of spider and parasitoid wasps prey on this species. The redback is one of few arachnids which usually display sexual cannibalism while mating. The sperm is then stored in the spermathecae, organs of the female reproductive tract, and can be used up to two years later to fertilise several clutches of eggs. Each clutch averages 250 eggs and is housed in a round white silken egg sac. The redback spider has a widespread distribution in Australia, and inadvertent introductions have led to established colonies in New Zealand, Japan, and in greenhouses in Belgium.
The redback is one of the few spider species that can be seriously harmful to humans, and its preferred habitat has led it to being responsible for the large majority of serious spider bites in Australia. Predominantly neurotoxic to vertebrates, the venom gives rise to the syndrome of latrodectism in humans; this starts with pain around the bite site, which typically becomes severe and progresses up the bitten limb and persists for over 24 hours. Sweating in localised patches of skin occasionally occurs and is highly indicative of latrodectism. Generalised symptoms of nausea, vomiting, headache, and agitation may also occur and indicate severe poisoning. An antivenom has been available since 1956, and there have been no deaths directly due to redback bites since its introduction.
- 1 Taxonomy and naming
- 2 Description
- 3 Behaviour
- 4 Distribution and habitat
- 5 Predators and parasitoids
- 6 Bites to humans
- 7 Bites to animals
- 8 Historical treatment of bites
- 9 Cultural impact
- 10 See also
- 11 Notes
- 12 References
- 13 External links
Taxonomy and naming
The common name "redback" is derived from the distinctive red stripe along the dorsal aspect of its abdomen. Other common names include red-striped spider, red-spot spider, jockey spider, Murra-ngura spider, Kapara spider and the Kanna-jeri spider.
Before DNA analysis, the taxonomy of the widow spider genus Latrodectus had been unclear—changes in the number of species reflect the difficulty of using morphology to determine subdivisions within the genus. Substantial interest in their systematics was most likely prompted by the medical importance of these venomous spiders. Swedish arachnologist Tamerlan Thorell described the redback spider in 1870 from specimens collected in Rockhampton and Bowen in central Queensland. He named it Latrodectus hasseltii in honour of colleague A.W.M. van Hasselt. In the same paper, he named a female from Cape York with an all-black abdomen L. scelio, now regarded as the same species. These specimens are in the Naturhistoriska Riksmuseet in Stockholm.
German arachnologist Friedrich Dahl revised the genus in 1902 and named L. ancorifer from New Guinea, which was later regarded as a subspecies of the redback. Another subspecies, L. h. aruensis, was described by Norwegian entomologist Embrik Strand in 1911. Subspecies indica (of L. scelio) had been described by Eugène Simon in 1897, but its origin is unclear. Frederick Octavius Pickard-Cambridge questioned Dahl's separating species on what he considered minor anatomical details but Dahl dismissed Pickard-Cambridge as an "ignoramus". Pickard-Cambridge was unsure whether L. hasseltii warranted species status, though he confirmed scelio and hasseltii as a single species, other researchers such as Ludwig Carl Christian Koch noting the differences to be inconsistent. The redback was also considered by some to be conspecific with the katipo (L. katipo), which is native to New Zealand, though Koch regarded them as distinct.
Reviewing the genus Lactrodectus in 1959, arachnologist Herbert Walter Levi concluded that the colour variations were largely continuous across the world and were not suitable for distinguishing the individual species. Instead, he focussed on differences in the morphology of the female sexual organs, and revised the number of recognised species from 22 to 6. This included reclassifying the redback and several other species as subspecies of the best-known member of the group, the black widow spider (Latrodectus mactans), found in North America and other regions. He did not consider the subspecies L. h. ancorifer, L. h. aruensis and L. h. indicus distinct enough to warrant recognition. Subsequently, more reliable genetic studies have split the genus into about 30 species, and the redback has no recognised subspecies in modern classifications.
A member of the genus Latrodectus in the family Theridiidae, the redback belongs in a clade with the black widow spider, with the katipo as its closest relative. A 2004 molecular study supports the redback's status as a distinct species, as does the unique abdomen-presenting behaviour of the male during mating. The close relationship between the two species is shown when mating: the male redback is able to successfully mate with a female katipo producing hybrid offspring. However, the male katipo is too heavy to mate with the female redback, as it triggers a predatory response in the female when it approaches the web, causing the female to eat it. There is evidence of interbreeding between katipo and redbacks in the wild.
The adult female redback has a body around 1 centimetre (0.4 in) long, with slender legs, the first pair of which are longer than the rest. The round abdomen is a deep black (occasionally brownish), with a red (sometimes orange) longitudinal stripe on the upper surface and an hourglass-shaped red/orange streak on the underside. Females with incomplete markings or all-black abdomens occasionally occur. The cephalothorax is much smaller than the abdomen, and is black. Redback spiderlings are grey with dark spots, and become darker with each moult. Juvenile females have additional white markings on the abdomen. The bright red colours may serve as a warning to potential predators. Each spider has a pair of venom glands each attached to each of its chelicerae with very small fangs. Small compared to the female, the male redback is 3–4 mm (0.12–0.16 in) long and is light brown, with white markings on the upper side of the abdomen and a pale hourglass marking on the underside.
The redback is mainly nocturnal; the female remains concealed during the day, and spins her web during the night, usually remaining in the same location for most of her adult life. Classified as a gum-footed tangle web, the web is an irregular-looking tangle of fine but strong silk. Although the threads seem random, they are strategically placed for support and entrapment of prey. The rear portion of the web forms a funnel-like retreat area where the spider and egg sacs are found. This area has vertical, sticky catching threads that run to ground attachments. The vertical strands act as trip wires to initially alert the spider to the presence of prey or threats. They also snare and haul prey into the air when weaker horizontal strands that hold them down, known as guy lines, break when prey thrash around. These webs are usually placed between two flat surfaces, one beneath the other. The female spends more time in the funnel and less time moving around during cooler weather.
Redbacks usually prey on insects, but can capture larger animals that become entangled in the web, including trapdoor spiders, small lizards, and even on rare occasion snakes. One web was recorded as containing a dead mouse. The woodlouse (Porcellio scaber) is a particularly common food item. Developing spiderlings need size-appropriate prey, and laboratory studies show that they are willing to consume common fruit flies (Drosophila melanogaster), mealworm larvae (Tenebrio molitor), muscoid flies and early nymphs of cockroaches. Food scraps and lighting attract insect prey to areas of human activity, which brings the redbacks. Once alerted to a creature becoming ensnared in a trap line, the redback advances to around a leg's length from its target, touching it and squirting a superglue-like material[clarification needed] over it to immobilise it. It then bites its victim repeatedly on the head, body and leg joints and wraps it in sticky and dry silk. Unlike other spiders, it does not rotate its prey while wrapping in silk, but like other spiders, it then injects a venom that liquefies its victim's innards. Once it has trussed the prey, the redback takes it to its retreat and begins sucking out the liquefied insides, generally 5 to 20 minutes after first attacking it. Redback spiders do not usually drink, except when starved.
Commonly, prey-stealing occurs where larger females take food items stored in other spiders' webs. When they encounter other spiders of the same species, often including those of the opposite sex, they engage in battle, and the defeated spider is eaten. If a male redback is accepted by a female, it is permitted to feed on the victims snared in the female's web. Baby spiders also steal food from their mother, which she tries to prevent. They also consume sticky silk as well as small midges and flies. Spiderlings are cannibalistic, more active ones sometimes eating their less active siblings.
Spiderlings hatch from their eggs after about 8 days and can emerge from the egg sac as early as 11 days after being laid, although cooler temperatures can significantly slow their development so that emergence does not occur for months. After hatching they spend about a week inside the egg sac, feeding on the yolk and molting once. Baby spiders appear from September to January (spring to early summer). Male spiders mature through five instars in about 45–90 days. Females mature through seven–eight instars in about 75–120 days. Males live for up to six or seven months, while females may live between two and three years. Laboratory tests have shown that redbacks may survive for an average of 100 days, and sometimes over 300 days without any food, those starved at 10 °C faring better than those kept without food at 25 °C. Spiders are known to reduce their metabolic rates in response to starvation, and can distend their abdomens to store large amounts of food. Redbacks can survive temperatures from below freezing point to 40 °C, though they do need relatively warm summers, with temperatures of 15 to 25 °C for two to three months, to survive and breed.
Redback spiderlings cohabit on the maternal web for several days to a week, during which time sibling cannibalism is often observed. They then leave by being carried on the wind. They follow light and climb to the top of nearby logs or rocks before extending their abdomens high in the air and producing a droplet of silk. The liquid silk is drawn out into a long gossamer thread that, when long enough, carries the spider away. This behaviour is known as ballooning or kiting. Eventually, the silken thread will adhere to an object where the young spider will establish its own web. They sometimes work cooperatively, climbing, releasing silk and being carried off in clusters. Juvenile spiders build webs, sometimes with other spiders.
Before a juvenile male leaves its mother's web, it builds a small sperm web on which it deposits its sperm from its gonads and then collects it back into each of its two palps (copulatory organs), because the gonads and palps are not internally connected. After it moults into its last instar, it sets off wandering to seek a female. The male spider does not eat during this period. How males find females is unclear, and it is possible they may balloon like juveniles. A Western Australian field study found that most males took 6 to 8 weeks to travel around 3 to 3.5 metres (10–11.5 ft) with occasional journeys of over 8 m (25 ft), but that only around 11–13% successfully found a mate. They are attracted by pheromones, which are secreted by unmated sexually-mature female redback spiders onto their webs and include a serine derivative (N-3-methylbutyryl-O-(S)-2-methylbutyryl-L-serine). This is thought to be the sole method by which males assess a female's reproductive status, and their courtship dismantles much of the pheremone-marked web.
During mating, the male redback attempts to copulate by inserting one of its palps into the one of the female's two spermathecae (sperm storage organs), each of which has its own insemination orifice. It then tries and often succeeds in inserting the other palp into the female's second orifice. The redback spider is one of only two animals known where the male has been found to actively assist the female in sexual cannibalism. In the process of mating, the much smaller male somersaults to place his abdomen over the female's mouthparts. In about two of three cases, the female fully consumes the male while mating continues. Males which are not eaten die of their injuries soon after mating. Sacrifice during mating is thought to confer two advantages to the males. The first is the eating process allows for a longer period of copulation and thus fertilisation of more eggs. The second is females which have eaten a male are more likely to reject subsequent males. Although this prohibits future mating for the males, this is not a serious disadvantage, because the spiders are sufficiently sparse that less than 20% of males ever find a potential mate during their lifetimes, and in any case, the male is functionally sterile if he has used the contents of both of his palps in the first mating.
Some redback males have been observed using an alternative tactic that also ensures more of their genetic material is passed on. Juvenile female redbacks nearing their final moulting and adulthood have fully formed reproductive organs, but lack openings in the exoskeleton that allow access to the organs. Males will bite through the exoskeleton and deliver sperm without performing the somersault seen in males mating with adult females. The females then moult within a few days and deliver a clutch of fertilised eggs.
Once the female has mated, the sperm is stored in one or both of her spermathecae. The sperm can be used to fertilise several batches of eggs, over a period of up to two years (estimated from observations of closely related species), but typically restarts the female's pheromone production advertising her sexual availability about three months after mating. A female spider may lay four to ten egg sacs, each of which is around 1 cm (0.4 in) in diameter and contains on average around 250 eggs, though can be as few as 40 or as many as 500. She prepares a shallow concave disc around 3 mm (1/8 in) in diameter before laying eggs into it over a period of around five minutes before laying more silk to complete the sac, which becomes spherical, the whole process taking around one and a quarter hours. She can produce a new egg sac as early as one to three weeks after her last.
Distribution and habitat
The redback spider is probably native to Australia; however, it has been suggested that it may have been spread to Australia by human activities, because it was first found at seaports. Queensland researchers Robert Raven and Julie-Ann Gallon also argued its preference for habitats altered by humans to be further evidence of this. Spider expert Barbara York Main queried that were it indeed introduced, it would be odd that Australia was missing from the worldwide distribution of Latrodectus species. The redback's close relationship with the New Zealand katipo also supports the native status of both in their respective countries.
The species was known by 1850 in South Australia, only 14 years after European settlement there, but had not been reported in early spider collections in other colonies. Outside urban areas, the redback is more often found in drier habitats ranging from sclerophyll forest to desert, even as harsh as the Simpson Desert. It became much more common in urban areas in the early decades of the 20th century, and is now found in all but the most inhospitable environments in Australia and its cities. It is particularly common in Brisbane, Perth and Alice Springs. The redback spider is commonly found in close proximity to human residences. Webs are usually built in dry, dark, sheltered sites, such as among rocks, in logs, tree hollows, shrubs, old tyres, sheds, outhouses, empty tins and boxes, children's toys or under rubbish or litter. Letterboxes and the undersurface of toilet seats are common sites. Populations can be controlled by clearing these habitats, squashing the spiders and their egg sacs, and using pesticide in outhouses. The CSIRO Division of Entomology recommends against the use of spider pesticides due to their toxicity, and because redbacks are rapid recolonists anyway.
Spiders in the French territory of New Caledonia in the Pacific were identified as L. hasselti in 1920, based on morphology. Their behaviour differs from Australian redbacks, as they do not engage in sexual cannibalism and are less prone to biting humans. The first recorded envenomation in New Caledonia was in 2007.
The redback spider's affinity for human-modified habitat has enabled it to spread to several countries via international shipping and trade. Furthermore, its tolerance to cold means that it has the ability to colonise many temperate countries with a winter climate cooler than Australia. This is concerning due to the risks to people being bitten who are unaware of its venomous nature, and also to the conservation of local threatened insect species that the redback might prey upon.
Redback spiders are also found in small colonies in areas of New Zealand. They are frequently intercepted by quarantine authorities, often among steel or car shipments. They were introduced into New Zealand in the early 1980s and now are found around Central Otago (including Alexandra, Bannockburn and near Wanaka) in the South Island and New Plymouth in the North Island. Authorities in the United Arab Emirates warn residents and visitors of redback spiders, which have been present since 1990. Colonies have also been established in greenhouses in Belgium, and isolated observations indicate possible presence in New Guinea, the Philippines, and India. Some redbacks were found in Preston, Lancashire, England, after a container of parts arrived from Australia; some may have escaped into the countryside before pest controllers could destroy them. One redback was recently found in a back garden in Dartford in Kent. Two females were discovered in the Iranian port city of Bandar Abbas in 2010.
There is an established population of redback spiders in Osaka, Japan, thought to have arrived in cargoes of wood chips. In 2008, redback spiders were found in Fukuoka, Japan. Over 700 have been found near the container terminal in Hakata Bay, Fukuoka City. Dispersal mechanisms within Japan are unclear, but redbacks are thought to have spread by walking or by being carried on vehicles. In September 2012, a woman was hospitalised after being bitten in the Higashi Ward of Fukuoka City. Signs warning about redback spiders have been posted in parks around the city, as Japan previously had no dangerous spiders.
Predators and parasitoids
The black house spider (Badumna insignis), daddy-long-legs spider (Pholcus phalangioides) and the giant daddy-long-legs spider (Artema atlanta) are known to prey on the redback spider, and redbacks are often absent if these species are present in significant numbers. Agenioideus nigricornis, a spider wasp, is a parasitoid of the adult redback. Other wasps of the families Eurytomidae and Ichneumonidae parasitise redback eggs, and mantid lacewings (Neuroptera and Mantispidae) prey on redback eggs.
Bites to humans
The redback spider is responsible for far more envenomations requiring antivenom than any other creature in Australia. Estimates of the number of people thought to be bitten by redback spiders each year across Australia range from 2,000 to 10,000. The larger female spider is responsible for almost all cases of redback spider bites. The smaller male was thought to be unable to envenomate a human, although some cases have been reported; their rarity is probably due to the male's smaller size and proportionally smaller fangs, rather than the male being incapable of biting or lacking potent venom. The bite from both juvenile and mature females appear to have similar potency. The male bite usually only produces short-lived, mild pain. Most bites occur in the warmer months between December and April, in the afternoon or evening. As the female redback is slow-moving and rarely leaves her web, bites generally occur as a result of placing a hand or other body part too close to the web, such as when reaching into dark holes or wall cavities. Bites often also occur when a hidden spider is disturbed in objects such as clothes, shoes, gloves, building materials or garden tools.
A 2004 review reported 46% of bites occurring on distal extremities of the limbs, 25% on proximal areas of limbs (upper arms and thighs), 21% on the trunk, and 7% on the head or neck. In some cases the same spider bites a victim multiple times. Historically, victims were often bitten on the genitalia, though this phenomenon disappeared as outhouses were superseded by plumbed indoor toilets. Conversely, bites on the head and neck have increased with use of safety helmets and ear muffs. Precautions to avoid being bitten include wearing gloves and shoes while gardening, not leaving clothes on the floor, and shaking out gloves or shoes before putting them on. Also, children can be educated not to touch spiders.
The redback and its relatives in the genus Lactrodectus are among the most dangerous spider genera, alongside funnel-web spiders (Atrax and Hadronyche), mouse spiders (Missulena), banana spiders (Phoneutria) and recluse spiders (Loxosceles). Venom is produced by holocrine glands in the spider's chelicerae (mouth parts). Venom accumulates in the lumen of the glands and passes through paired ducts into the spider's two hollow fangs. The venom of the redback spider is thought to be similar to that of the other Latrodectus spiders. It contains a complex mixture of cellular constituents, enzymes and number of high-molecular-weight toxins, including insect toxins and a vertebrate neurotoxin called alpha-latrotoxin, which is active in humans.
In vertebrates, alpha-latrotoxin produces its effect through destabilisation of cell membranes and degranulation of nerve terminals, resulting in excessive release of neurotransmitters, namely acetylcholine, norepinephrine and GABA. Excess neurotransmitter activity leads to the clinical manifestations of envenomation, although the precise mechanisms are not well-understood. Female redbacks have an average of around 0.08–0.10 mg of venom, and experiments indicate that the median lethal dose (LD50) for mice at room temperature is 10–20% of this quantity (0.27–0.91 mg/kg based on the mass of the mice used), but that it is considerably more deadly for mice kept at lower or higher temperatures. Pure alpha-latrotoxin has an LD50 in mice of 20–40 µg/kg.
The specific variant of the vertebrate toxin found in the redback was cloned and sequenced in 2012, and was found to be a sequence of 1180 amino acids, with a strong similarity to the equivalent molecule across the Latrodectus mactans clade. The syndromes caused by bites from any spiders of the Latrodectus genus have similarities; there is some evidence there is a higher incidence of sweating, and local and radiating pain with the redback, while black widow envenomation results in more back and abdominal pain, and abdominal rigidity is a feature common with bites from the west coast button spider (Latrodectus indistinctus) of South Africa.
One crustacean-specific and two insect-specific neurotoxins have been recovered from the Mediterranean black widow (L. tredecimguttatus), as have small peptides that inhibit angiotensin-1-converting enzyme;[a] the venom of the redback, although little-studied, likely has similar agents.
Redback antivenom was developed by Commonwealth Serum Laboratories, then a government body involved with discovering antivenoms for many venomous Australian creatures. Production involves the milking of venom from thousands of redbacks and repeatedly inoculating horses with non-lethal doses of it. The horses' immune systems make polyclonal antibodies. Blood plasma, containing the antibodies, is extracted by plasmapheresis. The plasma is treated with pepsin, and the active F(ab')2 fragments are separated and purified. Each vial contains 500 units of redback antivenom in approximately 1.5 ml, which is enough to inactivate 5 mg redback spider venom. The antivenom has been safely administered to women in various stages of pregnancy.
Redback antivenom has been widely used in Australia for decades, although evidence from controlled studies for its effectiveness has been lacking. Further studies are needed to confirm or refute its effectiveness. It appears clinically active against arachnidism caused by Steatoda spiders; however, as these cases are often mild and the evidence of its effectiveness is limited, this treatment is not recommended. Similarly, the antivenom has been effective with those of L. katipo, and L. tredecimguttatus. Animal studies also support its use against envenomation from other widow spiders, having successfully been tested against venom from L. mactans, L. hesperus, and L. lugubris.
Signs and symptoms
Envenomation from a redback spider bite produces a syndrome known as latrodectism; a half to two-thirds of people bitten develop significant pain or systemic symptoms. The diagnosis is made from the clinical condition, often based on the victim being aware of a bite and ideally with identification of the spider. Laboratory tests are rarely needed and there is no specific test for the venom or latrodectism.
The redback's small size means that swelling or puncture marks at the bite site are uncommon. The bite may be painful from the start, but more often only feels like a pinprick or mild burning sensation. Within an hour, a more severe local pain may develop with local sweating and sometimes piloerection (goosebumps)—these three symptoms together are a classic presentation of redback spider envenomation. Pain, swelling and redness can spread proximally up a limb or away from the bite site and regional lymph nodes may become painful. Some subjects with delayed symptoms may present with a characteristic sweating and pain in the lower limbs, generally below the knees, or a burning sensation in the soles of the feet. This may eventuate even if the person was bitten somewhere else on their body.
Around one in three subjects develops systemic envenomation; this may occur after a number of hours, or rarely, be delayed for more than 24 hours; symptoms typically include nausea, vomiting, abdominal or chest pain, agitation, headache, generalised sweating and hypertension. Severe pain usually persists for over 24 hours after being bitten, and symptoms of envenomation may linger for weeks or even months. Rare complications include seizure, coma, pulmonary edema, respiratory failure or localised skin infection. Children, the elderly, or those with serious medical conditions are at much higher risk of severe effects and death resulting from a bite. Infants have died within hours of a bite, but adult fatalities have taken up to 30 days.
Children and infants may be unable to report being bitten, making it difficult to associate their symptoms with a spider bite. Symptoms seen in infants include inconsolable crying, refusing to feed and a general erythematous rash.[b] Muscle aches and pains, and neck spasm are often seen in children over four years of age.
Unlike those of some other Australian spiders, redback bites do not necrose. Latrodectism has been misdiagnosed as various medical conditions including acute hepatitis, sepsis, testicular torsion or an acute abdomen.
Treatment is based on the severity of poisoning from the bite; the majority of cases do not require medical care, and patients with localised pain, swelling and redness usually only require local application of ice and simple oral analgesia such as paracetamol. Pressure immobilisation of the wound site is not recommended, as the venom spreads very slowly and is not affected. Keeping the victim still to reduce the spread of the venom is beneficial.
Hospital assessment is recommended if simple pain relief does not resolve local pain, or clinical features of systemic envenoming occur. Opioid analgesics may be necessary to relieve pain. Antivenom is generally given for adults suffering severe local pain or symptoms of systemic envenomation consistent with latrodectism, which include pain and swelling spreading proximally from site, distressing local or systemic pain refractory to simple analgesia, chest pain, abdominal pain, or excessive sweating (diaphoresis). A significant proportion of bites will not result in envenomation or any symptoms developing; around 2–20% of bite victims require treatment with the antivenom.[c] In an Australian study of 750 emergency hospital admissions for spider bites where the spider was definitively identified, 56 were from redbacks. Of these, 37 had significant pain lasting over 24 hours, but only six were treated with the antivenom.
The antivenom manufacturer's product information recommends one vial, although this is often insufficient. Hence current guidelines indicate two vials, with a further two vials recommended if symptoms do not resolve within two hours. The antivenom can be given by injection intramuscularly (IM) or intravenously (IV). The manufacturer recommends IM use, with IV administration reserved for life-threatening cases. However, toxicologist Geoffrey Isbister has suggested IM antivenom is not as effective as IV antivenom, after finding that IM antivenom takes longer to reach the blood serum. These concerns have led two handbooks to recommend IV in preference to IM administration in Australian practice.[d] Despite a long history of usage and anecdotal evidence of effectiveness, there is a lack of data from controlled studies confirming the antivenom's benefits. Before the introduction of antivenom, benzodiazepines and intravenous calcium gluconate were used to relieve symptoms of pain and distress, although calcium is not recommended as its benefit has not been shown in clinical trials.
Studies support the safety of antivenom, with around a 5% chance of an acute reaction, 1–2% of anaphylaxis and 10% chance of a delayed reaction due to serum sickness. Nevertheless, it is recommended that an injection of adrenaline is ready and available in case it is needed to treat a severe anaphylactic reaction, and also that the antivenom from the vial is administered diluted in a 100 ml bag of intravenous solution for infusion over 30 minutes. While it is rare that patients report symptoms of envenomation lasting weeks or month following a bite, there are case reports from the 1990s in which antivenom was reported to be effective in the relief of chronic symptoms when administered weeks or months after a bite, however, in the vast majority of cases, it is administered within 24 hours.
In almost all cases, symptoms resolve within a week. Fatalities are very unlikely; no deaths have been reported since the introduction of antivenom in 1956,[e] but before this, redback spider bites had resulted in at least 14 deaths in Australia.
Bites to animals
Redback spider bites are difficult to diagnose in pets unless witnessed. Dogs appear to have some resistance. They are at serious risk only if bitten many times, and rarely need antivenom. Cats are likely to be more susceptible and require antivenom, which can reverse symptoms very quickly. Guinea pigs, horses and camels are very susceptible. As with humans, the symptoms are predominantly autonomic in nature alongside pain at the bite site. Dogs may also suffer vomiting and diarrhoea, muscle tremors or clonic contractions, and abdominal wall rigidity, while cats may display salivate excessively, protrude their tongue or be overexcitable.
Historical treatment of bites
Most traditional or historical first-aid treatments for redback spider bites are either useless or dangerous. These include making incisions and promoting bleeding, using ligatures, applying alkaline solutions, providing warmth, and sucking the venom out. In modern first aid, incising, sucking, applying bandages and tourniqueting are strongly discouraged. In 1893, the Camperdown Chronicle reported that a doctor noticed that a severely ill benumbed victim got much better overnight following treatment using injections of strychnine and cocaine; strychnine had been popular as a snake bite antidote, but it was not effective. As of 2011, administration of magnesium sulphate was reported to have had some benefit though evidence of effectiveness is weak.
Indigenous Australians in New South Wales mixed the venom with that of snakes and pine tree gum to form a broth used to coat spear tips. Slim Newton drew popular attention to redbacks with his song "The Redback on the Toilet Seat", which won the Golden Guitar at the first Country Music Awards of Australia in 1973. Newton recalled an occasion when a friend used his outside toilet where the light globe had blown and reported he was lucky there was not a redback spider on the toilet seat. The phrase inspired him to write the song. A sculpture of an impossibly large redback, one of Australia's big things, was built in 1996 at Eight Mile Plains, Queensland. The Angels 1991 album Red Back Fever takes its name from the spider. Matilda Bay Brewing Company produces a wheat beer called Redback, with the distinctive red stripe as the logo. The redback appears in the name and emblem of the South Australia cricket team. The Airborne Redback, an Australian ultralight trike, was also named after the spider. Redback Boots is an Australian workboot manufacturing company, which uses the spider in its name and logo. In 2006 a redback spider stamp was designed as part of a "Dangerous Australians" stamp series, but was withheld from general circulation by Australia Post due to concerns that the realistic depiction would scare people opening their letter boxes.
- These likely make the venom stronger by altering the victim's physiology. Angiotensin-converting-enzyme inhibitors, or ACE inhibitors, are a class of widely-prescribed medications used in hypertension and heart failure.
- Published studies specifically looking at effects in children have been retrospective only and too limited to draw conclusive results. A ten-year retrospective study of children bitten and admitted to hospital in Perth found that the clinical features resemble those of adult cases, and 21% required antivenom—a rate similar to adult use, while a ten-year retrospective study from Alice Springs Hospital found that 83% required antivenom therapy, with irritability, hypertension and sweating as the most common clinical symptoms.
- The exact fraction of bites that require antivenom is difficult to quantify, because many bites are unreported. Figures from the manufacturer show that 344 cases required antivenom treatment in 1995, and in 2011 the figure was around 200. Estimates for the total number of bites range from 2,000 to 10,000. These estimates correspond to a broad range of about 2–17%, and reports have generally expressed this as "around" or "under" 20%. Two studies of redback victims who attended hospitals found that 6/23 (26%) and 32/150 (21%) received antivenom.
- A 2006 questionnaire found that of 218 Emergency physicians, 34 used the antivenom IM exclusively, 36 used IM then IV, 63 IV exclusively and 80 had no preference—that is, there was no consensus for preferred route.
- No deaths since 1956 have been formally reported, but a spider expert at the CSIRO Division of Entomology told a news reporter that he had heard of one death.
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