Anelosimus

Distinguished from other Theridiidae by the combination of small body size, notched abdominal band pattern, and absence of colulus. Social species may be identified by the presence of multiple individuals of varying ages within a single web structure. Species-level identification requires examination of genitalia and often geographic context.

Small spiders ranging from 1.8 to 7.5 mm in body length. Abdomen bears a notched red or brown band dorsally, appearing dark when preserved in alcohol. Lateral abdomen displays a white band and/or white blotches. Members of this genus lack a colulus, a silk-producing structure found in some other theridiids.

Habitat varies dramatically by social system and geography. Social species inhabit lowland tropical forests, particularly in the Americas. Subsocial species occur in montane tropical forests and at relatively high latitudes in temperate regions. Solitary species have been documented in beachfront habitats and at higher altitudes in northern latitudes. In Madagascar, many species are single-forest endemics.

Cosmopolitan distribution with major centers of diversity in the Americas (particularly South and Central America), Madagascar (10 described species, most endemic), and Australasia (Papua New Guinea, Australia, Bali). Additional species documented from Africa (Tanzania, Kenya, South Africa), Southeast Asia (Malaysia, Sulawesi), and East Asia (China, Japan). Records also exist from Europe.

Predatory, feeding on small insects captured in cobweb snares. Social species collectively capture medium-sized prey such as planthoppers and flies, with multiple individuals participating in subduing and consuming prey items. Prey immobilization typically involves bites to appendages, while consumption focuses on central body segments (thorax, abdomen, head) due to higher nutritional value.

Females encase eggs in tough silk sacs. In social and subsocial species, maternal care includes tearing and puncturing egg sacs to assist spiderling emergence. Some social species feed spiderlings by regurgitation. Juvenile dispersal is delayed in social species, with young remaining in natal webs where survival and development rates exceed those of isolated individuals.

Social organization ranges from solitary through subsocial to quasisocial. Social species construct massive communal webs covering tree canopies, containing thousands of individuals. Cooperative behaviors include collective prey capture, shared brood care, and assisted egg sac opening. Social colonies exhibit female-biased sex ratios (up to 10:1) and high inbreeding. Non-aggressive contests over prey occur during collective feeding. Solitary species construct individual webs and lack cooperative behaviors.

Social species function as significant predators in tropical forest canopies, with collective webs capturing substantial insect biomass. Egg parasitoids in the genus Baeus (Hymenoptera: Scelionidae) have been documented attacking Anelosimus eggs, indicating trophic linkage to parasitoid food webs.

Social species occasionally produce spectacular communal webs that attract public attention, such as the 2007 Lake Tawakoni State Park web in Texas and a 2015 Maryland observation. These webs, while visually striking, pose no threat to humans. The genus serves as a primary model system for research on social evolution, with implications for understanding cooperative behavior across animal taxa.

• Other TheridiidaeLack the characteristic notched abdominal band and colulus absence; most are solitary without communal web construction
• StegodyphusAnother genus containing social spiders, but belongs to family Eresidae (velvet spiders) rather than Theridiidae, with different web architecture and social system characteristics

• social spiders
• cobweb spiders
• cooperative behavior
• social evolution
• Theridiidae
• tropical forest
• Madagascar endemism
• subsocial
• quasisocial
• communal webs

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Spooky spiders in a big web - Cob-web spiders, Anelosimus studiosus — Bug of the Week
• Anelosimus-darwini - Entomology Today
• Uncategorized | Blog - Part 13
• From Darwin to moramora (‘take it easy’): Ten new subsocial spider species from Madagascar | Blog
• Ten New Spider Species Found in Madagascar
• spiders Archives - Page 2 of 3 - Entomology Today
• Brain investment in Anelosimus spiders
• A new phylogeny of Anelosimus and the placement and behavior of Anelosimus vierae n. sp. from Uruguay (Araneae: Theridiidae)
• Systematics of new subsocial and solitary Australasian Anelosimus species (Araneae : Theridiidae)
• Two new species of Baeus (Hymenoptera: Scelionidae) from Southeastern Brazil parasitoids of Anelosimus (Araneae: Theridiidae)
• Behaviour of colonial and solitary spiders of the theridiid species Anelosimus eximius
• New species of Anelosimus (Araneae: Theridiidae) from Africa and Southeast Asia, with notes on sociality and color polymorphism
• Collective prey capture and feeding behaviours of Anelosimus jabaquara Levi 1956 (araneae: theridiidae)