Within the class Araneae which is almost exclusively solitary, some spiders have evolved to become social.
Despite it’s rarity, social spiders appear to have evolved many times.
Out of the 39,000 known species of spider, only 23 appear social or quasi-social, and these spiders span 8 families and 11 genera, and scientists think that social species have evolved 18 or 19 times.
More work has been done on the ecological factors that make social spiders advantageous. Most social spiders live in lower-elevation tropical regions with many insects and large insects, and towards the centers of forests where large webs can be supported.
Perhaps the ability to live socially (e.g. combine webs and not kill one-another) lies dormant in many species. One of the most dramatic examples is in a giant communal web discovered in Lake Tawakoni State Park in 2007.
Texas A&M entomologist Allen Dean found most of the spiders were in the Tetragnathidae family, but also found species from 11 other families in the web including: funnel web weavers, sac spiders, orb weavers, mesh web weavers, wolf spiders, pirate spiders, jumping spiders, and long-jawed orb weavers.
Three such webs were built in the park that season, and Dean speculate that they emerged from the right conditions of plentiful rains and over-abundant food supplies (4). A report of the incident was written up in the journal Southwestern Entomologist.