o cooperation than from aggression to cooperation.
Social spiders just about always build webs
Another common feature is heavy rain. Rain does not have to be frequent, but when it is really intense, it has the potential to seriously damage spider webs. When a tempest takes out the web and threatens a spider's survival, the ones with just a glimmer of social behaviour might fare just a little better than their isolationist peers.
As a result, some have hypothesised that rough weather favours cooperation, since in those conditions it is the spiders that share the task of maintaining and repairing their webs that fare best. "Many hands make light work of web repair," says Pruitt.
Then there is the web itself. There are only a couple of instances in which spiders that do not build webs have evolved to be sub-social. These web-less social spiders, living in places like the Australian deserts or in African scrub habitat, have to cope with unusual circumstances – like enormous prey or particularly aggressive raiding ants.
But these cases aside, social spiders just about always build webs. And most of these webs have complex, three-dimensional structures, like the cone-shaped A. eximius webs I encountered in the jungle.
Pruitt thinks that could be a simple matter of mechanics. It is easier for two spiders just on the cusp of evolving sociality to join their webs together if they exist in three dimensions than if they weave flatter, two-dimensional ones, like Charlotte's eponymous web.
Some combination of tolerance, prey size, rough weather, and web geometry combine to create the perfect storm for social behaviour to emerge in spiders.
Anyone can do any job, and all are capable of reproduction
Add in the fact that it is easier to defend yourself against predators in a group, and that communal webs offer spiders the relative safety of staying in one place rather than risking travelling away from the web onto which you are born to live somewhere else, and for some species, cooperation is a good deal.
These spiders, like A. eximius with its massive funnel pits of doom, may superficially seem to behave like social insects. But in truth they could hardly be more different.
Bees and ants sort into separate castes. Some are workers, some are soldiers (or drones), and then there is a reproductive class. Those not included in the reproductive class are sterile; they could not reproduce even if they wanted to.
Social spiders, meanwhile, are more egalitarian. Anyone can do any job, and all are capable of reproduction.
It is not that spider societies do not rely on the division of labour. It is just that those roles are not strictly governed as they are for the social insects.
Spider vocations are intimately tied to their efficiency at those vocations
And while some female social spiders do not wind up reproducing, it is not because they are physically or genetically incapable. Instead, it is usually just because they have not lived successful enough lives. It takes a lot of nutrition to make a few hundred spider babies, and a spider that does not have a rich enough diet is not really up to the task.
Instead, roles in spider colonies are usually sorted on the basis of age and sex. Researchers are increasingly coming to realise that social spiders also sort themselves according to their individual personalities. "They're incredibly well organised," says Pruitt.
By paying close attention to individual spiders, he and others have discovered that certain spiders are more likely to spend their days attacking predators, while others are more likely to repair the webs, help keep parasites away, clean the web, rear the young, and so on.
"Spider vocations are intimately tied to their efficiency at those vocations," he says.
In spite of a lack of genetic diversity, they exhibit this exquisite diversity in terms of their personalities
Though it is not yet clear whether those skills develop through experience or because of innate aptitude, some spiders are clearly in the construction business, some are hunters, others are on janitorial duty, and still o