Communal Spiders?

The majority of spider species are solitary -as adults, spiders avoid eachother, except for mating. Even then, the unlucky male usually woinds up being killed and eaten by his mate. There are a few species that live communally, how do these spiders recognize eachother? And avoid eating the others in the community?
How would such an arrangement have evolved? Do these spiders hare their prey?