Cobweb spiders (Theridiidae) are one of the most diverse spider families, not only in terms of species numbers (>2200 described and many undescribed species), but also for the range of behavior, ecology, and morphology represented within the group. Theridiids include the widow spiders (genus Latrodectus), known for their potent venom and sexual cannibalism (females of some species typically eat the males during or shortly after mating). Sexual cannibalism is actually much more common in Tidarren and Echinotheridion, two genera where juvenile males amputate one of their two pedipalps (sperm transfer organs). Like Latrodectus, Tidarren and Echinotheridion have females much larger than males, a phenomenon known as sexual size dimorphism. Theridiids also include the majority of social spider species, which live in large colonies composed mostly of juvenile and adult females that cooperate in hunting, web building, and brood care. They include the largest group of kleptoparasitic spiders, which steel prey from other species.
Theridiid spiders have a comb of serrated setae on the fourth tarsus. Similar combs can also be found in some related families (Nesticidae, Synotaxidae). The combs are used to throw sticky silk over prey. Theridiids may wrap their prey in silk before applying a poisonous bite (wrap attack), or bite first. The wrap attack allows theridiids to delay direct contact with prey until it is safely immobilized. The sticky silk used in the wrap attack comes from large, specially modified silk spigots that are uniquely elongate.
Most theridiids have a stridulatory (sound producing) organ where elevated setal bases on the front of the abdomen rub against ridges on the back of the carapace. These organs are often more strongly developed in males. During courtship, males signal females with stridulatory sounds and other vibrations; in some species, females signal back.
Theridiid webs are extremely variable but typically consist of a three dimensional mesh with gumfoot lines. Gumfoot lines are under tension and adorned with sticky droplets. Similar webs are made by nesticids. In some theridiids, the mesh part of the web may be a broad sheet or nearly spherical with gumfoot lines radiating out. Gumfoot lines and even sticky silk are absent from some theridiid webs. Some theridiid webs are reduced to a few lines. Hadrotarsines apparently do not build webs.
This is a large and diverse family of spiders, with thousands of species found all over the world. In Michigan there are several dozens species at least, and probably more still unknown to science.
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. In this group the abdomen is often very round. 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, and in mating, and are much bigger in male spiders than in females.
Cobweb weavers have eight eyes on the front of their cephalothorax, arranged in two rows of four. Below the eyes is the mouth and fangs that they use to bite their prey with. They all have venom to paralyze and digest their prey.
Female cobweb weavers are often much bigger than males. There is a lot of variation in color in this family, but many species are brownish-grey with various patterns of darker marks.
One important group of cobweb weavers in the widow spiders. They are one of the few groups of spiders whose venom can hurt people. Only female widow spiders bite. They are shiny black, and have red markings on the bottom of their round abdomen.
Range length: 2.0 to 15.0 mm.
Other Physical Features: bilateral symmetry
Sexual Dimorphism: female larger; sexes shaped differently
These spiders live in many different kinds of habitats, on the ground, on plants, in burrows and caves, pretty much anywhere they can spin their webs. They often build in dark, sheltered places, in piles of branches or basement corners. Some species in this group are common house spiders.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: taiga ; desert or dune ; chaparral ; forest ; rainforest ; scrub forest ; mountains
These spiders eat Insecta and other invertebrates. Some build nests that can trap flying insects, others stick lines down to the ground that snap up and pull prey into the web. A few species sneak into the webs of other spiders and steal their prey. When cobweb weavers catch a prey animal, they wrap it in sticky silk and bite it, injecting venom that paralyzes or kills the prey. They sometimes leave the prey wrapped up and hanging in the web and eat it later. No other family uses sticky silk to wrap their prey, they just use regular silk that doesn't have glue on it.
These spiders rely on camouflage colors to avoid predators. They also sometimes build a special hiding place in their webs. Some species put bits of soil or plant parts in their web to hide it. The few species with strong venom have warning colors and will bite if threatened.
- other Araneae
- praying mantids
- small Squamata
- small mammals especially Soricidae
Life History and Behavior
Communication and Perception
Like all spiders, cobweb weavers are sensitive to vibrations and touch. They probably also use chemical sense to communicate, and they can see, but not too well. Some species in this family have special body parts they can rub together to make noise or vibrations. No one knows exactly what they are for.
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.
Male cobweb spiders rarely live more than a year, but in some species females can live for three years or more.
Mating System: polyandrous
Male cobweb weavers leave their webs and go looking for females. If they find one, they approach very cautiously, because sometimes females eat the males.
Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; sexual ; fertilization (Internal ); oviparous ; sperm-storing
Female cobweb weavers lay eggs. They produce clutches of upto to 250 eggs at a time, and place them in egg sacks made of brownish silk. They hang the egg sacks in their web and guard them. In some species the female also feeds her babies after they hatch. They get digested food from her until they have grown enough to shed their skin the first time. After they shed they go off on their own. This is unusual, no other family of spiders is known to feed their offspring.
Parental Investment: female parental care
Evolution and Systematics
Discussion of Phylogenetic Relationships
Despite major advances in the past few years, theridiid phylogeny is still a work in progress. Recent studies have analyzed data from morphology (Agnarsson, 2004), molecules (Arnedo et al., 2004), and both in combination (Agnarsson, 2006). These studies largely agree on the composition of subfamilies. The phylogenetic hypothesis illustrated above is simplified from Agnarsson (2006), the only published study combining molecular and morphological data.
Molecular Biology and Genetics
Statistics of barcoding coverage
|Specimen Records:||4,380||Public Records:||585|
|Specimens with Sequences:||3,257||Public Species:||117|
|Specimens with Barcodes:||3,044||Public BINs:||106|
|Species With Barcodes:||283|
No species in this family are known to be in danger of extinction.
Relevance to Humans and Ecosystems
Economic Importance for Humans: Negative
Some people don't like to have these spiders making cobwebs in their house. Also, a few species can give people a dangerous bite.
Negative Impacts: injures humans (bites or stings)
Economic Importance for Humans: Positive
This family of spiders includes lots of species that eat insects in agricultural fields. They are important in controlling pest insects.
Positive Impacts: controls pest population
Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. The diverse family includes over 2200 species in over 100 genera) of three-dimensional space-web-builders found throughout the world. Theridiid spiders are entelegyne (have a genital plate in the female) araneomorph ecribellate (use sticky capture silk instead of woolly silk) spiders that often build tangle space webs and have a comb of serrated bristles (setae) on the tarsus of the fourth leg.
The family includes some model organisms for research, for example, the genus Latrodectus, the medically important widow spiders. In addition to studies characterizing their venom and its clinical manifestation, widow spiders are broadly used in research on spider silk, and on sexual biology including sexual cannibalism.
Anelosimus spiders are also model organisms, used for the study of sociality, its evolution, and its ecological and evolutionary causes and consequences. They are particularly important for such studies as the genus contains species varying from solitary to permanently social, and because sociality has evolved frequently within the genus allowing comparative studies across species. These spiders are also a promising model for the study of inbreeding as their mating system co-varies with sociality, and all permanently social species are highly inbred.
One species in Theridion, the Hawaiian T. grallator, is used as a model to understand the selective forces and the genetic basis of color polymorphism within species. Theridion grallator is known as the "happyface" spider, as certain morphs have a pattern uncannily resembling a smiley face or a grinning clown face on their yellow body.
The family also contains the well studied kleptoparasitic species of the subfamily Argyrodinae (including Argyrodes, Faiditus, and Neospintharus) which often have triangular bodies. These spiders live in the webs of larger spiders and pilfer small prey caught by their host's web, eat prey killed by the host spider, and may consume silk from the host web, as well as attack and eat the host itself.
The largest genus with over 600 species currently placed in it is Theridion, but it is not monophyletic. Another large genus is Parasteatoda, previously Achaearanea, which includes the North American common house spider.
Many theridiids trap ants and other ground dwelling insects by means of elastic sticky silk trap lines leading to the soil surface. Despite their name, cobweb or tangle-web spiders have a huge range of web architectures.
Webs[edit source | edit]
Theridiid are probably the only family with a large diversity of spider web forms: there is a high within-taxon diversity (e.g. in Latrodectus), as well as convergence in different taxa. Theridiid gumfoot-webs consist of frame lines that anchor them to surroundings and of support threads, which possess viscid silk. Four main web types are currently recognized: among webs with gumfooted lines, there are webs with a central retreat (Achaearanea-type) and those with a peripheral retreat (Latrodectus-type). Among webs without gumfooted lines, there are those that contain viscid silk (Theridion-type) and those with a sheet-like structure, which do not contain visible viscid silk (Coleosoma-type). However, there are many undescribed web forms.
Building of gumfooted lines constitutes a unique stereotyped behaviour and is most probably homologous for Theridiidae and its sister family Nesticidae. Webs remain in place for extended periods and are expanded and repaired, but no regular pattern of web replacement has been observed. 
Genera[edit source | edit]
Recent years have seen advances in the systematics of cobweb spiders with phylogenies reconstructed using both morphological and molecular data. The following classification is built on these results (see also Joel Hallan's Biology Catalog).
- Anatea Berland, 1927
- Audifia Keyserling, 1884
- Dipoena Thorell, 1869
- Dipoenata Wunderlich, 1988
- Emertonella Bryant, 1945
- Euryopis Menge, 1868
- Eurypoena Wunderlich, 1992
- Gmogala Keyserling, 1890
- Guaraniella Baert, 1984
- Hadrotarsus Thorell, 1881
- Lasaeola Simon, 1881
- Phycosoma O. P.-Cambridge, 1879
- Yaginumena Yoshida, 2002
- Yoroa Baert, 1984
- Latrodectinae Petrunkevitch, 1928
- Pholcommatinae Simon, 1894
- Asygyna Agnarsson, 2006
- Carniella Thaler & Steinberger, 1988
- Cerocida Simon, 1894
- Craspedisia Simon, 1894
- Enoplognatha Pavesi, 1880
- Helvidia Thorell, 1890
- Pholcomma Thorell, 1869
- Phoroncidia Westwood, 1835
- Proboscidula Miller, 1970
- Robertus O. P.-Cambridge, 1879
- Selkirkiella Berland, 1924
- Styposis Simon, 1894
- Theonoe Simon, 1881
- Wirada Keyserling, 1886
- Achaearanea Strand, 1929
- Achaearyopa Barrion & Litsinger, 1995
- Ameridion Wunderlich, 1995
- Cabello Levi, 1964
- Cephalobares O. P.-Cambridge, 1870
- Chrysso O. P.-Cambridge, 1882
- Coleosoma O. P.-Cambridge, 1882
- Cyllognatha L. Koch, 1872
- Dipoenura Simon, 1908
- Echinotheridion Levi, 1963
- Exalbidion Wunderlich, 1995
- Helvibis Keyserling, 1884
- Histagonia Simon, 1895
- Jamaitidion Wunderlich, 1995
- Keijia Yoshida, 2001
- Macaridion Wunderlich, 1992
- Molione Thorell, 1892
- Neottiura Menge, 1868
- Nesticodes Archer, 1950
- Nipponidion Yoshida, 2001
- Paratheridula Levi, 1957
- Propostira Simon, 1894
- Rugathodes Archer, 1950
- Sardinidion Wunderlich, 1995
- Simitidion Wunderlich, 1992
- Takayus Yoshida, 2001
- Tekellina Levi, 1957
- Theridion Walckenaer, 1805
- Theridula Emerton, 1882
- Thymoites Keyserling, 1884
- Tidarren Chamberlin & Ivie, 1934
- Wamba O. P.-Cambridge, 1896
- Anelosimus Simon, 1891
- Astodipoena Petrunkevitch, 1958 † (fossil, Eocene)
- Chorizopella Lawrence, 1947
- Clya Koch & Berendt, 1854 † (fossil, Eocene)
- Coscinida Simon, 1895
- Eodipoena Petrunkevitch, 1942 † (fossil, Eocene)
- Eoysmena Petrunkevitch, 1942 † (fossil, Eocene)
- Flegia Koch & Berendt, 1854 † (fossil, Eocene)
- Hetschkia Keyserling, 1886
- Icona Forster, 1955
- Kochiura Archer, 1950
- Landoppo Barrion & Litsinger, 1995
- Marianana Georgescu, 1989
- Mictodipoena Petrunkevitch, 1958 † (fossil, Eocene)
- Municeps Petrunkevitch, 1942 † (fossil, Eocene)
- Nactodipoena Petrunkevitch, 1942 † (fossil, Eocene)
- Paidiscura Archer, 1950
- Tomoxena Simon, 1895
- Zercidium Benoit, 1977
See also[edit source | edit]
References[edit source | edit]
- Grimaldi, D.A. et al. Fossiliferous Cretaceous Amber from Myanmar (Burma): Its Rediscovery, Biotic Diversity, and Paleontological Significance. American Museum Novitates, No 3361, 2002
- Cirrus Digital Tangle Web Spider Enoplognatha ovata
- Platnick, Norman I. "The World Spider Catalog". Retrieved 2009-08-11.
- Benjamin, Suresh P. & Zschokke, Samuel 2002. Untangling the tangle-web: web building behaviour of the comb-footed spider Steatoda triangulosa and comments on phylogenetic implications (Araneae: Theridiidae). Journal of Insect Behavior, 15: 791-809 
- Benjamin, Suresh P. & Zschokke, Samuel 2003. Webs of theridiid spiders: construction, structure and evolution. Biological Journal of the Linnean Society, 78: 293-305 
- Agnarsson I. 2006a. A revision of the New World eximius lineage of Anelosimus (Araneae, Theridiidae) and a phylogenetic analysis using worldwide exemplars. Zoological Journal of the Linnean Society 146: 453-593. PDF
- Agnarsson I. 2006b. Asymmetric female genitalia and other remarkable morphology in a new genus of cobweb spiders (Theridiidae, Araneae) from Madagascar. Biological Journal of the Linnean Society 87: 211-232. PDF
- Agnarsson I. 2006c. Phylogenetic placement of Echinotheridion (Araneae: Theridiidae) - do male sexual organ removal, emasculation, and sexual cannibalism in Echinotheridion and Tidarren represent evolutionary replicas? Invertebrate Systematics 20: 415-429. PDF
- Agnarsson I. 2004. Morphological phylogeny of cobweb spiders and their relatives (Araneae, Araneoidea, Theridiidae). Zoological Journal of the Linnean Society 141: 447-626. PDF
- Cooperative behavior of Anelosimus jabaquara (2002). PDF
- Arnedo, M.A., Coddington, J., Agnarsson, I. & Gillespie, R.G. (2004). From a comb to a tree: phylogenetic relationships of the comb-footed spiders (Araneae, Theridiidae) inferred from nuclear and mitochondrial genes. Molecular Phylogenetics and Evolution 31:225-245. PDF
- Arnedo MA, Agnarsson I, Gillespie RG. In Press. Molecular insights into the phylogenetic structure of the spider genus Theridion (Araneae, Theridiidae) and the origin of the Hawaiian Theridion-like fauna. Zoologica Scripta.
- Aviles, L., Maddison, W.P. and Agnarsson, I. 2006. A new independently derived social spider with explosive colony proliferation and a female size dimorphism. Biotropica, 38: 743-753.
- Benjamin, S.P. and Zschokke, S. 2003. Webs of theridiid spiders: construction, structure and evolution. Biological Journal of the Linnean Society, 78: 293-305.
- Blackledge, T.A., Swindeman, J.E. and Hayashi, C.Y. 2005. Quasistatic and continuous dynamic characterization of the mechanical properties of silk from the cobweb of the black widow spider Latrodectus hesperus. Journal of Experimental Biology, 208: 1937-1949.
- Blackledge, T.A. and Zevenbergen, J.M. 2007. Condition dependent spider web architecture in the western black widow Latrodectus hesperus. Animal Behaviour, 73: 855-864.
- Gillespie, R.G. and Tabashnik, B.E. 1994. Foraging Behavior of the Hawaiian Happy Face Spider (Araneae, Theridiidae). Annals of the Entomological Society of America, 87: 815-822.
- Gillespie, R.G. and Tabashnik, B.E. 1989. What makes a happy face? Determinants of color pattern in the Hawaiian happy face spider Theridion grallator (Araneae, Theridiidae). Heredity, 62: 355-364.
- Grostal, P. and Walter, D.E. 1997. Kleptoparasites or commensals? Effects of Argyrodes antipodianus (Araneae: Theridiidae) on nephila plumipes (Araneae: Tetragnathidae). Oecologia, 111: 570-574.
- Oxford, G.S. and Gillespie, R.G. 1996. Quantum shifts in the genetic control of a colour polymorphism in Theridion grallator (Araneae: Theridiidae), the Hawaiian happy-face spider. Heredity, 76: 249-256.
- Oxford, G.S. and Gillespie, R.G. 1996. Genetics of a colour polymorphism in Theridion grallator (Araneae: Theridiidae), the Hawaiian happy-face spider, from greater Maui. Heredity, 76: 238-248.
- Purcell, J. and Aviles, L. 2007. Smaller colonies and more solitary living mark higher elevation populations of a social spider. Journal of Animal Ecology, 76: 590-597.
- Vollrath, F. 1979. Behavior of the Kleptoparasitic Spider Argyrodes-Elevatus (Araneae, Theridiidae). Animal Behaviour, 27: 515-521.