Theridiidae

Sundevall, 1833

tangle-web spiders, cobweb spiders, comb-footed spiders

Genus Guides

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Theridiidae is a large, globally distributed of araneomorph spiders comprising over 2,600 in more than 130 . Members are characterized by a comb of serrated bristles (setae) on the of the fourth leg, used to manipulate silk. The family exhibits remarkable diversity in web architecture, ranging from irregular tangle webs to specialized gumfoot webs and sheet-like structures. Theridiids are ecribellate, producing sticky capture silk rather than woolly silk, and are entelegyne with females possessing a genital plate. The family includes medically significant species such as widow spiders (Latrodectus), model organisms for social research (Anelosimus), and specialized kleptoparasites (Argyrodinae).

Thymoites unimaculatus by (c) Bill Keim, some rights reserved (CC BY). Used under a CC-BY license.Latrodectus geometricus by no rights reserved, uploaded by Jesse Rorabaugh. Used under a CC0 license.Platnickina by (c) Ben Armstrong, some rights reserved (CC BY), uploaded by Ben Armstrong. Used under a CC-BY license.

Pronunciation

How to pronounce Theridiidae: /ˌθɛrɪˈdaɪɨdiː/

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Identification

The presence of a comb of serrated setae on the of the fourth leg is the primary diagnostic feature distinguishing Theridiidae from other spider . This structure is visible under magnification and is used to manipulate silk during web construction. Additional characteristics include: ecribellate condition (lacking a cribellum, producing sticky capture silk rather than woolly silk); entelegyne genitalia in females; and typically three-dimensional, irregular web architecture. Members can be distinguished from similar families (Linyphiidae, Nesticidae) by the combination of comb feet, web structure, and genital . Molecular phylogenetic studies support the monophyly of the family.

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Appearance

Theridiids typically possess a comb of serrated bristles (setae) on the of the fourth leg, a diagnostic feature used to comb silk from . Body size varies considerably across the , from diminutive like Argyrodes (2-4 mm body length) to larger members such as Latrodectus. The family exhibits extensive morphological diversity, with body forms ranging from globular (Steatoda, Parasteatoda) to more elongated shapes (Enoplognatha). Coloration is highly variable, including cryptic browns and grays, bold patterns (Theridion grallator with smiley- markings), and distinctive warning coloration in widow spiders (red hourglass markings).

Habitat

Theridiids occupy extraordinarily diverse across all continents except Antarctica. Many are , being among the most common arthropods in human dwellings worldwide. Habitat preferences range from caves (troglobitic such as Troglotheridion in Yunnan-Guizhou Plateau, China, showing and pigment loss) to forest understory vegetation, meadows, and arid regions. Web placement varies by guild: gumfoot web builders (Latrodectus-type, Achaearanea-type) favor sheltered locations with vertical substrates; tangle-web builders occupy corners and recesses; kleptoparasitic species inhabit spider webs.

Distribution

Global distribution on all continents except Antarctica. The 's distribution has been substantially influenced by human activity, with numerous achieving or introduced ranges through commerce. Notable distribution patterns include: Latrodectus species native to multiple regions with some introduced ; Parasteatoda tepidariorum suspected to be of South American origin but now cosmopolitan; Steatoda nobilis and expanding in urban of Ireland and elsewhere; and radiations in isolated systems such as Hawaiian Theridion species.

Seasonality

Activity patterns vary by and climate. Temperate species typically show peak activity from late spring through early autumn, with mating occurring during this period. Some species produce multiple sacs across the reproductive season (e.g., Parasteatoda tepidariorum from late spring through late summer). Spiderlings of outdoor species such as Enoplognatha ovata emerge in autumn and overwinter in protected ground-level . Indoor may reproduce year-round given stable conditions.

Diet

Theridiids are , with diet varying by foraging strategy. Web-building capture flying and ground-dwelling insects; gumfoot traplines specifically target ants and other ground-dwelling insects. Some species show prey specialization: Euryopis species are , using ambush tactics and silk bonding to subdue aggressive ant prey including harvester ants (Pogonomyrmex). Kleptoparasitic members of Argyrodinae steal captured prey from spider webs, with some species specializing on host sacs (Argyrodes pluto feeding on Latrodectus hesperus eggs and juveniles).

Host Associations

Life Cycle

details vary considerably across the . General pattern: females deposit in silk sacs, with egg number ranging from approximately 30 (Steatoda triangulosa) to over 600 (Parasteatoda tepidariorum). Egg sac varies—spherical and opaque white in Steatoda triangulosa, tan and papery pear-shaped in Parasteatoda tepidariorum, white and hemispherical with silk tufts in Euryopis. Spiderlings emerge and may disperse immediately or overwinter in protected locations. Social in Anelosimus show extended maternal care and delayed . Sexual maturity timing varies: brown widow spiders (Latrodectus geometricus) reach reproductive maturity 16% sooner than southern black widows (L. mactans).

Behavior

Web-building shows exceptional diversity. Gumfoot-web construction involves stereotyped building of viscid silk support threads with central (Achaearanea-type) or peripheral (Latrodectus-type) retreats; this behavior is likely homologous with sister Nesticidae. Kleptoparasitic exhibit specialized behaviors: Argyrodes pluto displaces sacs to web periphery to feed on eggs and juveniles. Some theridiids display social behavior: Anelosimus species range from solitary to permanently social with cooperative web maintenance and care. -hunting Euryopis species use a distinctive ambush technique, flinging silk to bond ants to substrate before biting. Sexual has been documented in widow spiders, though frequency in natural settings appears lower than laboratory observations. Brown widow spiders (Latrodectus geometricus) show targeted aggression toward black widows, killing them in 80% of sub- pairings.

Ecological Role

Theridiids function as in diverse , with -level impacts varying by guild. Web-building contribute to in human dwellings and natural . - Euryopis species may influence ant colony dynamics. Kleptoparasitic Argyrodinae affect spider : host Nephila plumipes with Argyrodes antipodianus show reduced weight gain and increased web relocation. Some theridiids serve as prey for (Zatypota alborhombarta). such as Steatoda nobilis and Latrodectus geometricus are altering structure in introduced ranges, with brown widows displacing native black widows through direct rather than resource competition.

Human Relevance

Theridiids are the most common arthropods in human dwellings worldwide, making them frequently encountered spiders. Medical significance: widow spiders (Latrodectus) possess venom causing latrodectism, though bites are rare and fatalities extremely uncommon with modern treatment. Brown widow venom causes less severe reactions than black widow venom. Steatoda (false widows) are frequently mistaken for widow spiders but are not considered dangerously venomous. The Common House Spider (Parasteatoda tepidariorum) and Triangulate Cobweb Weaver (Steatoda triangulosa) are benign inhabitants of buildings. Several species serve as model organisms: Latrodectus for venom and silk research, sexual , and sexual studies; Anelosimus for sociality and inbreeding research; Theridion grallator for color studies. Some species have been evaluated for potential (Steatoda triangulosa against , though deemed unlikely to be effective).

Similar Taxa

  • Linyphiidae (sheet-web weavers)Build similar tangled webs but lack comb feet (serrated setae on fourth ) and have distinct genital
  • Nesticidae (cave cobweb spiders)Share gumfoot web architecture and are sister to Theridiidae; distinguished by morphological and molecular characters, though some theridiids (Troglotheridion) show convergent cave adaptations
  • Pholcidae (cellar spiders)Share habits and irregular webs but have extremely long, thin legs, different arrangement, and lack comb feet

Misconceptions

Sexual in widow spiders is frequently overstated; while observed in laboratory settings, it appears rare in nature and associated with male escape inability rather than female predatory intent. The name 'black widow' derives from this misconception. Many Steatoda are unnecessarily feared due to resemblance to widow spiders; they lack the red hourglass marking and are not dangerously venomous. The term 'cobweb spider' is sometimes applied too broadly to any spider in a messy web, but properly refers to Theridiidae with comb feet.

More Details

Web architecture diversity

Theridiidae exhibits exceptional diversity in web form, including: gumfoot webs with viscid silk traplines (Latrodectus-type, Achaearanea-type); tangle webs without gumfoot lines containing viscid silk (Theridion-type); sheet-like webs without viscid silk (Coleosoma-type); and specialized 'cocoon webs' induced by in Cryptachaea jequirituba. Web forms remain in place for extended periods with expansion and repair, but no regular replacement pattern has been observed.

Taxonomic instability

Generic placement has been historically unstable for many theridiids. Parasteatoda tepidariorum has been assigned to Theridion, Achaearanea, and Parasteatoda. The large Theridion (over 600 ) is not monophyletic. Recent molecular and morphological phylogenetic studies have restructured generic boundaries, with new genera described (Asiopisinus from East Asia, Troglotheridion from China) and numerous transfers between genera.

Interspecific aggression and displacement

Research demonstrates that brown widow spiders (Latrodectus geometricus) actively seek out and kill southern black widows (L. mactans) at rates 6.6 times higher than other related , representing a rare case of direct by an on a native driving displacement.

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