Eight legs, eight eyes and a pair of venomous fangs – the average spider is so well-equipped that it's easy to see why arachnophobes are terrified. But there is one saving grace: at least spiders are solitary, so they are usually encountered in small numbers.
That's certainly what I thought.
But then I found myself trudging along a muddy path in the Peruvian Amazon jungle, face to face with a spider colony several thousand strong. Their funnel-shaped web arched from tree to tree, a structure containing too many of the creepy crawlies to count.
These were spiders but not as I knew them: they appeared to function as a society, just like ants or bees.
Most spiders are indeed lone wolves, but a scant handful have evolved a level of sociality to rival ant colonies, bee hives, or even primate societies.
Communal spiders work together to build, maintain, and clean their webs
Anelosimus eximius, the species I encountered in the rainforest, is not the only kind of social spider in the world, but it does construct the biggest webs. Some can reach more than 25ft (7.6m) feet long and 5ft (1.5m) wide. A web that size could contain as many as 50,000 individual spiders. That is a lot of legs, eyes and fangs.
A. eximius was first discovered more than a century ago by a French arachnologist named Eugène Simon. More social spiders have been discovered since. One was found as recently as 2006, in Ecuador, by entomologist Leticia Avilés.
Sociality shows up in at least seven spider families. In all we know of around 25 social species among the 45,000 described spider species on the planet. Sociality evolved at least a dozen separate times among them.
While the details vary from species to species among the social spiders, many of their features are similar.
For example, an A. eximius colony contains adult males and females as well as youngsters, but the majority of spiders on the web are females. In the early 1980s, researchers found that males comprise only between 5% and 22% of any colony's populace.
Communal spiders work together to build, maintain, and clean their webs. They cooperate in capturing prey, and dine together when they snare a large feast.
The females feed their offspring by vomiting up food for them, just like mother birds. They even regurgitate food for juveniles other than their own. In other words, they work together to care for the youngest in the colony. It is a sort of spider day-care.
Nearby colonies tend to be related to each other, because new colonies form in one of two ways.
Sometimes, a large web is broken in half, perhaps by heavy rainfall or falling branches, or even a falling monkey. In its place, two smaller colonies are left behind.
My students know more about social spiders than your average arachnologist
Other times, individual females will strike out on their own, setting up a new web. Eventually other dispersing females will join the group; perhaps ones who tried to set up their own webs but failed. Survival is more likely in groups, after all.
These two processes together help to explain why A. eximius colonies tend to be found in clusters, sometimes as many as 40 related colonies within just a few kilometres.
A. eximius is perhaps the best known of the social spiders, but that is not saying much.
Gregarious arachnids are not much studied – perhaps because so few of them exist in the first place. "My students know more about social spiders than your average arachnologist," says Linda Rayor, an entomologist at Cornell University in Ithaca, New York, who studies Australia's social huntsman spiders.
Why was the bee subject to such an awful fate?
"Most animals are solitary," she tells me, "whether you're looking at mammals, or birds, or whatever. Social behaviour in otherwise solitary animals is cool."
Cool indeed, if somewhat creepy.
As I watched the social spiders go about their day deep in the jungle, a bee found itself stuck in the giant web. Suddenly, dozens of the eight-legged predators descended en masse onto the struggling black-and-yellow striped insect. It was impossible to see through the writhin