g mass of tiny spider legs, but one thing was certain: that bee was done for.
If death by one spider seems bad enough, it must be nothing compared to an attack by a whole swarm of them.
Why was the bee subject to such an awful fate? Or, to put it another way, how and why did a few spiders become social when the overwhelming majority of their fellow species are solitary?
The first spider, the proto-spider, was probably solitary. So the spiders that gave rise to today's truly social species must have been too. But then they did something remarkable: they turned sub-social: they learned to tolerate each other, at least for a time – even if they did not exactly enjoy hanging out in groups.
As they mature, they become intolerant of each other
That early tolerance could have come about as a result of parental care. In some spiders alive today, that is just defending an egg sac, but in others – the ones that are poised to evolve sociality – it looks more familiar to our mammal brains.
In those species, females provide food and protection for their developing offspring, and occasionally even to other juveniles. In some species, mothers even make the ultimate sacrifice, allowing themselves in their last moments to become a meal for their brood. Sub-social spiders can still be cannibals, after all.
"They're the spiders that already have cooperation as juveniles," says arachnologist Jonathan Pruitt of the University of California, Santa Barbara. "But as they mature, they become intolerant of each other."
In other words, juvenile tolerance alone is not enough to turn spiders fully social. The environment in which the spiders live also has to be right. Researchers have discovered three ecological elements that often lead to cooperative living among arachnids.
Social spiders tend to feed on bigger prey, for one thing.
Solitary spiders living in places where it is difficult to subdue large or more profitable prey alone may eventually figure out that it is in their interest to work together. It is a smaller step from tolerance to 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. 