African Social Spiders: these spiders form all-female colonies that hunt, forage, maintain the web, and raise their offspring as a group, without any dominance hierarchy or caste system
Communal behavior is extremely rare among spiders, but this species (Stegodyphus dumicola) is one of the few known examples of a true "social spider." The females live in communal nests that can contain up to 2,000 individuals, and they all work together to hunt, forage, build their webs, and raise their babies.
Above: an African social spider feeding some of the young spiderlings in her colony by regurgitating food into their mouths
African social spiders can be found in the arid regions of southwestern Africa, where their dense silk nests are often built in the branches of thorn trees and shrubs. Most of the spiders in these colonies are female (more than 85%) and they are often closely related to one another.
This species also has a female-biased primary sex ratio, with female embryos developing in more than 80% of the eggs that the spiders produce. The male offspring leave the nest just before reaching maturity, and each male lives alone after that.
Above: African social spiders working together to subdue their prey, which will ultimately be taken back to the nest and shared with the rest of the colony
The entire colony works together to complete a variety of tasks. No spider is exclusively assigned to a single role, but some of them spend more time participating in certain tasks than others, depending on their physical size and condition. They subdue and retrieve any prey that gets caught in the web, repair, maintain, and expand the web itself, engage in foraging, and tend to the colony's offspring.
There is no evidence that any social hierarchy or caste system exists within these communities. There are no queens, and none of the spiders' roles are assigned by birth.
Above: Stegodyphus dumicola
African social spiders are particularly devoted when it comes to their maternal duties. They engage in extreme allomaternal care, which means that they share the responsibility of caring for the colony's offspring, and maternal care is provided by both mothers and non-mothers. The spiders tend to one another's eggsacs, regurgitate food for the spiderlings, and even engage in matriphagy, which means that they eventually allow themselves to be eaten by the growing brood.
As this article describes:
Some proportion of the females do not reproduce – sometimes as much as 60% – but remain as helpers, contributing to foraging and brood care (allo-mothering). Both breeding females and virgin allo-mothers regurgitate food for colony offspring and eventually let the young consume their bodies. Even subadult females provide regurgitation feeding to colony offspring.
Young that are raised with both mothers and allo-mothers show higher survival and growth than young raised by their mothers alone, suggesting a clear fitness benefit of cooperative breeding.
Sources & More Info:
Science Direct: Social Spiders
Current Biology: Quick Guide to Social Spiders
Phys.org: Untangling the Social Lives of Spiders
Proceedings of the Royal Society: The Age and Evolution of Sociality in Stegodyphus Spiders
Entomology Today: Social Spiders Divide Labor According to Body Size and Condition
Animal Behaviour: Extreme Allomaternal Care by Unmated Females in a Cooperatively Breeding Spider
National Geographic: Baby Spiders Eat their Mothers
University of Portsmouth: Social Spiders Have Different Ways of Hunting in Groups
Behavioral Ecology: Spider Societies Mitigate Risk by Prioritizing Caution
Behavioral Processes: Warring Arthropod Societies
Behavioral Ecology and Sociobiology: Does the African Social Spider Stegodyphus dumicola Control the Sex of Individual Offspring?
