Linyphiidae Blackwall, 1859
Linyphiidae Blackwall, 1859
The spider family Linyphiidae (sheetweb weavers) has a worldwide distribution and includes 4461 described species according to Platnick (2013), making it the second most species-rich spider family after the Salticidae (jumping spiders). The greatest number of linyphiid species are found in north temperate regions. Nearly a thousand linyphiid species are known to occur in North America north of Mexico, making Linyphiidae the most diverse spider family in this region, since only a few hundred salticids occur here. (Draney and Buckle 2005; Bradley 2013).
Many of the larger linyphiids are in the subfamily Linyphiinae, a group that includes around a third of linyphiids, among them several very familiar North American representatives such as the Hammock Spider (Pityohyphantes costatus), the Bowl and Doily Spider (Frontinella communis), and the Filmy Dome Spider (Neriene radiata). Around two thirds of linyphiids are placed in the subfamily Erigoninae ("dwarf sheetweavers"), which were formerly treated as the "micryphantids". Dwarf sheetweaver are among the world's smallest spiders, some of them measuring less than 1 mm long when fully grown. Dwarf sheetweavers either build inconspicuous webs near the ground or no web at all. They are most often noticed when ballooning: when conditions are just right (most often in autumn when the sun creates a warm rising air current), thousands of tiny ballooning spiders may drift down together and coat a fence or field with silk. This silk coating ("gossamer") is composed of thousands of thin silk strands. Close examination of a gossamer sheet can reveal hundreds of spiders running about trailing silk (and often becoming airborne again). (Bradley 2013)
Linyphiids often have large chelicerae with numerous teeth that can be seen under moderate magification. The eight small eyes are usually positioned far up on the face, above the tall clypeus that is typical of this group. The combination of tall chelicerae and high clypeus gives sheetweb weavers a a distinctive face. Some dwarf sheetweaver males have unusual head morphologies with horns, lumps, or pits. This ornamentation is related to mating. Females may grasp these head ornamentations with their fangs during mating and in a few species the pits have been shown to contain numerous glands, which may secrete female attractants. (Bradley 2013)
Linyphiids construct semi-permanent webs consisting of one or more horizontal sheets of silk which are often supported above and below by auxiliary support lines. The spider generally hangs upside down beneath the primary sheet (or near the edge). There is usually a tangle of knockdown threads either above and/or below the sheet. The knockdown threads intercept flying insects, which blunder into them and are slowed or tumble down onto the sheet. Similar threads under the sheet may act to warn the spider of approaching danger or prey emerging from below. When a prey item strikes the web, the spider rushes out to capture it. Because the spider is beneath the sheet, it bites through the web to capture and subdue the prey, which is then pulled through the web, wrapped with more silk, and consumed. The sheet web silk is generally not sticky, but the prey is slowed by the difficulty of walking over the netlike sheet interspersed with trip lines. (Draney and Buckle 2005; Bradley 2013)
Most linyphiids live in leaf litter or on the ground, but some (especially larger species) build webs in vegetation. Both myrmecophiles (ant associates) and cavernicoles (cave-dwellers) are known. Linyphiids generally feed on small, soft bodied arthropods, especially collembolans and flies. They are found in nearly all habitats, but are most diverse and abundant in more mesic to hydric (i.e., wetland) areas and are prominent in northern peatlands. Most species are univoltine or annual (one generation/year), but multivoltine (more than one generation/year) and merovoltine (more than one year/generation) life histories are also common. Adults of most species are present for just a brief period each year, but some multivoltine and merovoltine species are active as adults during most or all of the year. Most species overwinter as juveniles or adults—some are even active under snow in winter—but a few overwinter as eggs. (Draney and Buckle 2005) Draney and Buckle (2005) reviewed the biology of linyphiids and cite key references as of 2005.
Linyphiidae is a large and taxonomically difficult family. Identification of genera and species is not for the faint of heart, but Draney and Buckle (2005) provide keys to the genera occurring in North America north of Mexico (and references for generic revisions where available). Although some genera have been recently revised, most have not. Several known genera and many species remain undescribed. Draney and Buckle (2005) reviewed the taxonomic history of North American linyphiids and provided a compilation of key references. Paquin and Dupérré (2003, 2006) illustrate all linyphiid species known from Quebec, providing a valuable resource for identifying linyphiids elsewhere in northern and eastern North America as well. LinyGen (Hormiga et al. 2008) is an online resource that includes illustration of all linyphiid genera worldwide.
Sheetweb weavers are one of the biggest families of spiders in the world, and they are found all around the world. There are at least 60 species in Michigan, and probably more that are not yet known.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native )
Sheetweb weavers are small, dark, shiny spiders that build interesting webs. They are less then 8 mm long. Like all spiders they have two body-segments, a cephalothorax in front and an abdomen behind. They have eight legs, all attached to the cephalothorax. On the front of the cephalothorax are the fangs, the eyes, and two small "mini-legs" called pedipalps. The pedipalps are used to grab prey, and in mating, and are much bigger in male spiders than in females. Sheetweb spiders have eight eyes in two rows of four. They have fangs that they use to bite their prey with, and venom glands. On their fangs are rough spots that they can rub together to make sounds.
It is impossible for us to tell the difference between a sheetweb weaver and a cobweb weaver except by looking at their webs (see below for more on sheetwebs).
Range length: 1.5 to 8.0 mm.
Other Physical Features: bilateral symmetry
Sheetweb weavers are found in all kinds of habitats: anywhere there are small insects and at least a little vegetation to build their webs on.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: tundra ; taiga ; desert or dune ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Spiders in this family spin small horizontal sheets of webbing, or domes (see the pictures for an example). They hang upside-down underneath the web, and when a small Insecta or other animal walks across it, they bite through the silk, then grab their prey and pull it through to eat it.
Sheetweb weavers hide underneath their webs, and sometimes make two layers of web and hide between them for protection. If disturbed by a larger animal they quickly drop down into nearby vegetation to get away.
- other Araneae
- small Amphibia
Life History and Behavior
Communication and Perception
These spiders have special structures on their fangs that they can rub together to make sounds to communicate with. They probably also use web vibrations, and certainly use taste and smell to communicate.
These spiders hatch from eggs, and 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, which they do many times during their lives.
These little spiders probably don't live much longer than a year.
Breeding interval: After mating, female sheetweb weavers lay eggs.
Breeding season: Probably Spring, Summer, or Fall
Key Reproductive Features: sexual ; fertilization (Internal ); oviparous
Females hide their eggs in special egg sacks made of silk, sometimes attached to their webs (and probably guarded by her) and sometimes just stuck to twisted grass stems and left alone.
Parental Investment: female parental care
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:13200
Specimens with Barcodes:12751
Species With Barcodes:788
No sheetweb weavers are known to be in danger, but there are still many species out there we don't know anything about.
Relevance to Humans and Ecosystems
Economic Importance for Humans: Positive
These are harmless little spiders that might help keep the population of small insects under control, but don't have any strong direct effects on humans.
Linyphiidae is a family of very small spiders, including more than 4,300 described species in 578 genera worldwide. This makes Linyphiidae the second largest family of spiders after the Salticidae. New species are still being discovered throughout the world, and the family is poorly known. Because of the difficulty in identifying such tiny spiders, there are regular changes in taxonomy as species are combined or divided.
Spiders in this family are commonly known as sheet weavers (from the shape of their webs), or money spiders (in the United Kingdom, Ireland, Australia, New Zealand, and in Portugal, from the superstition that if such a spider is seen running on you, it has come to spin you new clothes, meaning financial good fortune).
Common genera include Neriene, Lepthyphantes, Erigone, Eperigone, Bathyphantes, Troglohyphantes, the monotypic genus Tennesseellum and many others. These are among the most abundant spiders in the temperate regions, although many are also found in the tropics. The generally larger bodied members of the subfamily Linyphiinae are commonly found in classic "bowl and doily" webs or filmy domes. The usually tiny members of the Erigoninae are builders of tiny sheet webs. These tiny spiders (usually 3 mm or less) commonly balloon even as adults and may be very numerous in a given area on one day, only to disappear the next. Some males of the erigonines are exceptional, with their eyes set up on mounds or turrets. This reaches an extreme in some members of the large genus Walckenaeria, where several of the male's eyes are placed on a stalk taller than the carapace.
A few spiders in this family include:
- Bowl and doily spider, Frontinella communis
- Filmy dome spider, Neriene radiata
- Blacktailed red sheetweaver, Florinda coccinea
Spiders of this family occur nearly worldwide. In Norway many species have been found walking on snow at temperatures of down to -7 °C.
- Cirrus Digital, Sheetweb Spider - Drapetisca alteranda
- Hormiga 2000
- RSPB Birds magazine, Winter 2004
- Hormiga, G. (1998). The spider genus Napometa (Araneae, Araneoidea, Linyphiidae). Journal of Arachnology 26:125-132 PDF
- Hormiga, Gustavo (2000): Higher Level Phylogenetics of Erigonine Spiders (Araneae, Linyphiidae, Erigoninae). Smithsonian Contributions to Zoology 609. (160 pages) PDF
- Bosselaers, J & Henderickx, H. (2002) A new Savignia from Cretan caves (Araneae: Linyphiidae). Zootaxa 109:1-8 PDF
- Hågvar, S. & Aakra, K. 2006. Spiders active on snow in Southern Norway. Norw. J. Entomol. 53, 71-82.
- Platnick, Norman I. (2007): The world spider catalog, version 8.0. American Museum of Natural History.
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