While most of the 50,000 known spider species are solitary, some live in organized groups, forming what are known as colonies. These collective living arrangements represent a rare and unique social structure within the arachnid world.
Defining Spider Colonies
A spider colony is a group of spiders residing together in a shared environment, often characterized by an interconnected web structure. This communal living goes beyond simple aggregations; individuals actively participate in shared activities that benefit the entire group.
Colonial spiders construct and maintain extensive communal web structures, which can house tens of thousands of individuals. This shared silk framework serves as both a capture device for prey and a protective habitat for the colony members.
Many colonial species exhibit cooperative behaviors like collective hunting. For example, Anelosimus eximius cooperates in capturing prey, allowing them to subdue insects much larger than a single spider could manage. Stegodyphus sarasinorum also engages in communal predation and feeding within its colonies.
Some colonial spiders also display communal brood care, where multiple females share responsibility for eggs and young, including feeding young by regurgitation. A large, shared web and numerous individuals can also provide a collective alarm system against predators. The genus Stegodyphus includes several social species that form multi-generational colonies.
Advantages of Colonial Life
Living in a colony offers several advantages that drive the evolution of this social behavior in certain spider species. One significant benefit is enhanced prey capture. The expansive, communal web allows for trapping a greater number of insects or larger prey that would be unattainable for a solitary spider. Cooperative hunting, as seen in species like Anelosimus eximius, enables spiders to collectively subdue sizable prey, maximizing the total biomass captured per spider. This collective effort can even allow colonies to capture organisms as large as birds and bats.
Group living also provides improved defense against predators. The large, communal web acts as a collective warning system; vibrations caused by an approaching predator are transmitted across the web, alerting numerous individuals. Studies on the Mexican colonial spider Metepeira incrassata show that predator capture success decreases as colony size increases, with spiders in the web’s core exhibiting lower risk. Spiders in larger colonies react to predator-simulating vibrations at greater distances, indicating an early warning effect.
Communal care of offspring contributes to higher reproductive success. In species where females share brood care, such as Anelosimus eximius, young spiders are fed through regurgitation, and females may care for offspring other than their own. This shared responsibility can lead to increased survival rates for spiderlings, even though individual female fecundity might decrease in larger groups due to increased competition. The overall survival of colonies and late-instar juveniles improves with increasing colony size.
The collective web structure can also offer a degree of environmental regulation and protection. While not as extensively studied as other benefits, the dense, interconnected silk structures may provide some insulation from temperature fluctuations or offer shelter from strong winds and heavy rainfall. This collective modification of their microhabitat can contribute to the colony’s overall resilience against environmental stressors.