The family Araneidae (orbweavers) includes more than 3000 described species; nearly 7% of all known spider species are araneids (Platnick 2013). In North America north of Mexico, there are around 161 known araneid species placed in 31 genera. Of the seven families of spiders that spin flat orb webs, the Araneidae has the most species. Many araneids are fairly large and colorful and the family includes a number of familiar spiders. Most araneids have roundish bodies and fairly short, relatively thick legs. In some species, there is strong sexual size dimorphism, with males much smaller than females. (Bradley 2013) Like most spiders, araneids have eight eyes.
Many araneid species have distinctive dark patches and light spots on the underside of the abdomen. These are especially conspicuous when viewed with a flashlight or headlamp at night. For example, the larger Araneus species and all Neoscona have a large rectangular black area with white or yellowish spots or comma-shaped marks at each corner. Argiope have a black patch with many small pale spots. Other genera, such as Aculepeira and Metepeira, have a black patch with white lines. These markings are often helpful in recognizing genera, but are rarely sufficient to identify particular species. (Bradley 2013)
Orbweavers have relatively poor vision and sense their prey by their vibrations. When a potential food item hits a web, the spider rushes over and quickly wraps it in a cocoon of silk, biting and paralyzing it once it is sufficiently immobilized. The wrapped prey may be cut out of the web and brought back to the web hub or to a retreat, where the spider begins feeding. Unlike many spiders, araneids chew their food (Levi 2005). Sometimes a wrapped prey item is kept for some time before being consumed. Although most araneids build vertical orb webs, Mecynogea build a fine-meshed horizontal web and a few species spin reduced webs or capture prey in other ways (e.g., Mastophora bolas spiders, which attract male moths with scent and catch them by swinging a thread with an attached sticky ball at them as they approach). Nocturnal orbweavers may take down their webs in the morning and eat them, then re-build them in the evening; diurnal orbweavers rebuild their webs in the morning. (Levi 2005; Bradley 2013)
Most larger araneids in North America mature in summer and fall, but others mature in spring. Typical life span is one to two years. Dew-covered webs are easily located by walking toward the sun in the morning. Araneids are collected by beating branches or sweeping vegetation with a net. The American araneid fauna has been revised and illustrated by H.W. Levi and his students (1968 to present) and Dondale et al. (2003) have illustrated additional species. (Levi 2005)
The araneid Araneus cavaticus is perhaps the most famous spider in literature (at least in the English language), since this species was the model for Charlotte in Charlotte's Web by the 20th century American author E.B. White.
(Levi 2005; Bradley 2013)
Araneidae Clerck, 1757
Araneidae Clerck, 1757
Orb-weaving spiders are found all around the world. There are over 4000 species known, and probably at least that many still unknown to science. In Michigan there are at least 40 species known, and probably more still out there.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native )
All spiders have two body-segments, a cephalothorax in front and an abdomen behind. They have eight legs, all attached to the cephalothorax. On the front they have two small "mini-legs" called palps. These are used to grab prey. They are also used in mating. Palps are much bigger in male spiders than in females. All orbweavers have fangs that they use to bite their prey with. They all have venom glands that produce toxins. The toxins paralyze and digest their prey.
Orb-weavers are more diverse physically than the other groups of spiders. They usually have a fairly large abdomen, and it nearly always overlaps the back of the back edge of the cephalothorax. The shape of the abdomen varies a lot between species. Sometimes it is spiny, sometimes smooth, sometimes very irregular in shape. Nocturnal orb-weavers are usually brown or gray. Diurnal species are more brightly colored and may be black and yellow or orange. Often females are much larger than males in this group.
Range length: 3.0 to 30.0 mm.
Other Physical Features: bilateral symmetry
Sexual Dimorphism: female larger; sexes shaped differently
Orb-weavers live anywhere there are insects and places to put up their webs. They are much more common in humid habitats than in dry ones.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: tundra ; taiga ; desert or dune ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Wetlands: marsh ; swamp ; bog
These spiders catch and eat the Insecta they trap in their webs. When an insect touches the sticky web it gets caught. They spider quickly rushes in and starts spinning and wrapping the insect in more webbing to keep it trapped. The orb web is very distinctive, and is the easiest way to tell that a spider belongs to this group. Orb webs are flat, and have a neat spiral of sticky silk that goes around and around from the middle to the outer edge. Many species in this family build a new web every day or every night, and then take it down and eat it before hiding for the night or day.
Orb-weavers are predators that are usually low in the food web. They eat insects but are in turn eaten by other predators.
Many orb-weavers only put up their webs at night, in order to avoid birds. Orb-weavers with webs up in daylight are more brightly colored, maybe to warn predators of their venomous bite. If disturbed in their webs, many orb-weavers quickly drop away.
- predatory Hymenoptera
- parasitic Hymenoptera
- other Araneae
Animal / predator / stocks nest with
female of Episyron rufipes stocks nest with Araneidae
Based on studies in:
Canada: Ontario, Mad River (River)
This list may not be complete but is based on published studies.
Known prey organisms
Based on studies in:
Canada: Ontario, Mad River (River)
This list may not be complete but is based on published studies.
Life History and Behavior
Communication and Perception
Communication among orb-weavers is mostly by touch and web vibrations, though there are probably some chemical signals too. Their vision is not good enough for much visual communication.
Spiders hatch from eggs. The hatchlings look more or less like grown-up spiders, though sometimes their colors change as they age. To grow they have to shed their exoskeleton. They do this many times during their lives.
Adult Orb-weavers can't usually survive below-freezing weather, so they don't live for more than a year. In tropical regions with warm winters, they may live longer.
In Michigan most orbweavers probably mate in the summer, and females start producing their eggs later in the summer. They make round egg cases of silk, and put their hundreds of little eggs inside. The spiderlings often hatch before winter comes, but they stay inside the egg case until spring.
Breeding season: Late summer.
Key Reproductive Features: semelparous ; seasonal breeding ; year-round breeding ; sexual ; fertilization (Internal ); oviparous
Males do not contribute to care for the offspring in this group. Females will sometimes watch over their eggs as long as they can, but they die when it gets too cold (the babies survive in their egg sack).
Parental Investment: female parental care
Evolution and Systematics
Glue droplets on orb-weaver spider webs resist slippage through adhesion, elongation under load, and force transfer due to granules.
"Sticky viscous prey capture threads form the spiral elements of spider orb-webs and are responsible for retaining insects that strike a web. These threads are formed of regularly spaced aqueous droplets that surround a pair of supporting axial fibers. When a thread is flattened on a microscope slide a small, opaque granule can usually be seen within each droplet. These granules have been thought to be the glycoprotein glue that imparts thread adhesion. Both independent contrast and standard regressions showed that granule size is directly related to droplet volume and indicated that granule volume is about 15% of droplet volume. We attempted to find support for the hypothesized adhesive role of granules by establishing an association between the contact surface area and volume of these granules and the stickiness of the viscous threads of 16 species in the context of a six-variable model that describes thread stickiness. However, we found that granule size made either an insignificant or a small negative contribution to thread stickiness. Consequently, we hypothesize that granules serve to anchor larger, surrounding layers of transparent glycoprotein glue to the axial fibers of the thread, thereby equipping droplets to resist slippage on the axial fibers as these droplets generate adhesion, elongate under a load, and transfer force to the axial fibers." (Opell & Hendricks 2010:339)
Learn more about this functional adaptation.
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:7498
Specimens with Barcodes:7290
Species With Barcodes:366
No orb-weavers are known to be endangered, but since many species are still not known to scientists, there could be rare ones out there we don't know about.
Relevance to Humans and Ecosystems
Economic Importance for Humans: Negative
Orb-weaver spiders can bite, and are venomous, but none of them are known to be particularly dangerous to people.
Negative Impacts: injures humans (bites or stings)
Economic Importance for Humans: Positive
Orb-weavers, like most spiders, are important predators of pest insects.
Positive Impacts: controls pest population
The typical orb-weaver spiders (family Araneidae) are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields and forests. Their common name is taken from the round shape of this typical web, and the taxon was formerly also referred to as the Orbiculariae.
Orb-weavers have eight similar eyes, hairy or spiny legs, and no stridulating organs. The Araneidae family is cosmopolitan, including many well-known large or brightly colored garden spiders. The 3,006 species in 168 genera worldwide make Araneidae the third-largest family of spiders known (behind Salticidae and Linyphiidae). The orb-weavers include over 10,000 species and make up about 25% of spider diversity.
However, orb-webs are also produced by members of other families. The large golden orb-weavers (Nephilidae) and the long-jawed orb weavers (Tetragnathidae) were formerly included in the Araneidae; they are indeed closely related to them, being part of superfamily Araneoidea. Their webs are similar to those of the typical orb-weavers, but tend to be less sophisticated and often have an irregular instead of a neat spiral arrangement of the prey-capturing threads. The cribellate or hackled orb-weavers (Uloboridae) belong to a distinct superfamily of the suborder Araneomorphae; their webs are often very sophisticated, but Uloboridae use neither venom to kill their prey, nor sticky threads in their web, and probably evolved the orb structure independently. Uloboridae are cribellate, and their threads can be recognized by the fuzzy and dull appearance, which captures prey by a velcro-like mechanism.
Generally, orb-weaving spiders are three-clawed builders of flat webs with sticky spiral capture silk. The building of a web is an engineering feat, begun when the spider floats a line on the wind to another surface. The spider secures the line and then drops another line from the center, making a "Y". The rest of the scaffolding follows with many radii of nonsticky silk being constructed before a final spiral of sticky capture silk. The third claw is used to walk on the nonsticky part of the web. Characteristically, the prey insect that blunders into the sticky lines is stunned by a quick bite, and then wrapped in silk. If the prey is a venomous insect, such as a wasp, wrapping may precede biting.
Many orb-weavers build a new web each day. Most orb-weavers tend to be active during the evening hours; they hide for most of the day. Generally, towards evening, the spider will consume the old web, rest for approximately an hour, then spin a new web in the same general location. Thus, the webs of orb-weavers are generally free of the accumulation of detritus common to other species, such as black widow spiders.
Some orb-weavers do not build webs at all. Members of the genera Mastophora in the Americas, Cladomelea in Africa, and Ordgarius in Australia produce sticky globules, which contain a pheromone analog. The globule is hung from a silken thread dangled by the spider from its front legs. The pheromone analog attracts male moths of only a few species. These get stuck on the globule and are reeled in to be eaten. Interestingly, both types of bolas spiders are highly camouflaged and difficult to locate.
The spiny orb-weaving spiders in the genera Gasteracantha and Micrathena look like plant seeds or thorns hanging in their orb-webs. Some species of Gasteracantha have very long, horn-like spines protruding from their abdomens.
One feature of the webs of some orb-weavers is the stabilimentum, a crisscross band of silk through the center of the web. It is found in a number of genera, but Argiope, which includes the common garden spider of Europe, as well as the yellow and banded garden spiders of North America, is a prime example. The band has been hypothesized to be a lure for prey, a marker to warn birds away from the web, and a camouflage for the spider when it sits in the center of the web. However, recent research suggests the stabilimentum actually decreases the visibility of the silk to insects, thus making it harder for prey to avoid the web. The orb-web consists of a frame and supporting radii overlaid with a sticky capture spiral, and the silks used by orb-weaver spiders have exceptional mechanical properties to withstand the impact of flying prey.
The orb web derived from substrate-bound web, likely an irregular ground web or brushed sheet web. The change from a ground web to an aerial web allowed for both horizontal and vertical orb webs that could capture flying prey. During the Cretaceous, a radiation of angiosperm plants and their insect pollinators occurred. Fossil evidence shows that the orb web was in existence at this time, which permitted a concurrent radiation of the spider predators along with their insect prey. The capacity of orb webs to absorb the impact of flying prey led orbicularian spiders to become the dominant predators of aerial insects in many ecosystems. Insects and spiders have comparable rates of diversification, suggesting they co-radiated, and the peak of this radiation occurred 100 Mya before the origin of angiosperms. Vollrath and Selden (2007) make the bold proposition that insect evolution was driven less by flowering plants than by spider predation – particularly through orb webs – as a major selective force.
Most arachnid webs are vertical and the spiders usually hang with their head downward. A few webs, such as those of orb-weaver in the genus Metepiera have the orb hidden within a tangled space of web. Some Metepiera are semisocial and live in communal webs. In Mexico, such communal webs have been cut out of trees or bushes and used for living fly paper.
The oldest known true orb-weaver is Mesozygiella dunlopi, from the Lower Cretaceous. Several fossils provide direct evidence that the three major orb-weaving families, namely Araneidae, Tetragnathidae and Uloboridae, had evolved by this time, about 140 million years ago. They probably originated during the Jurassic ( ). Based on new molecular evidence in silk genes, all three families are very likely to have a common origin.
The two families, Deinopoidea and Araneoidea, have similar behavioral sequences and spinning apparatuses to produce architecturally similar webs. The Araneidae weave true viscid silk with an aqueous glue property, and the Deinopoidea use dry fibrils and sticky silk. The Deinopoidea (including the Uloboridae), have a cribellum – a flat, complex spinning plate from which the cribellate silk is released. They also have a calamistrum – an apparatus of bristles used to comb the cribellate silk from the cribellum. The Araneoidea, or the "ecribellate" spiders, do not have these two structures. The two families of orb-weaving spiders are morphologically very distinct, yet there is much similarity between their web form and web construction behavior. The cribellates retained the ancestral character, yet the cribellum was lost in the escribellates. The lack of a functional cribellum in araneoids is most likely synapomorphic. If the orb-weaver spiders are a monophyletic group, the fact that only some species in the group lost a feature adds to the controversy. The cribellates are split off as a separate taxon that retained the primitive feature, which makes the lineage paraphyletic and not synonymous with any real evolutionary lineage. The morphological and behavioral evidence surrounding orb webs led to the disagreement over a single origin or a dual origin. However, molecular analysis provides more support for a monophyletic origin.
- Araneinae Simon, 1895
- incertae sedis
- Glyptogona Simon, 1884
- Cyrtarachninae Simon
- Artonis Simon, 1895
- Colphepeira Archer, 1941
- Enacrosoma Mello-Leitão, 1932
- Encyosaccus Simon, 1895
- Melychiopharis Simon, 1895
- Micrepeira Schenkel, 1953
- Parmatergus Emerit, 1994
- Pronous Keyserling, 1881
- Sedasta Simon, 1894
- Singafrotypa Benoit, 1962
- Tethneus Scudder, 1890 † (fossil, Oligocene)
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|Wikimedia Commons has media related to Araneidae.|
|Wikispecies has information related to: Araneidae|
- The Life of the Spider by John Crompton. Mentor, 1950.
- "The Orb-Weaving Spiders of Canada and Alaska. Araneae: Uloboridae, Tetragnathidae, Araneidae, Theridiosomatidae. Insects and Arachnids of Canada Series, Part 23." By C. D. Dondale, J. H. Redner, P. Paquin, and H. W. Levi. NRC Research Press, Ottawa, 2003. ISBN 978-0-660-18898-0
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