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 others offer childcare services.
In species like A. eximius, spiders are essentially clones. Brothers and sisters mate with each other, generation after generation, so that colonies become highly inbred.
Since adolescent spiders do not go off in search of new colonies, there is no influx of new genetic material. For that reason, some suspect that spider personalities develop as a result of early life experiences, not genetics. "In spite of a lack of genetic diversity, they exhibit this exquisite diversity in terms of their personalities," Pruitt says.
In 2013, he and his colleagues looked at a social spider called Stegodyphus sarasinorum, native to India, Sri Lanka, and Nepal. They found that individual personality traits predict which job each spider performs.
S. sarasinorum is found in dry scrubland. But like the spiders I found in the rainforests of Peru, these arachnids work cooperatively to build and maintain their webs and to capture food.
Social spiders have distinct personalities
Using tiny dabs of paint applied to the spiders, Pruitt and his team were able to track 40 from each of two different wild colonies. Individuals that were bolder were more likely to be involved in attacking prey – but other characteristics, like body size or a spider's level of aggression, did not factor into their vocation.
"Responding to stimuli from a prey caught in the web elicits different responses according to a set of individual characteristics," they concluded.
In other words, social spiders have distinct personalities, which in turn help to define their roles in the community.
In a way, that is not so different from human societies. Bold, risk-taking people might be more likely to wind up fighting fires or enrolling in a police academy, while the more calculating, deliberative types wind up as lawyers or architects.
Despite lacking a backbone, invertebrates like insects and arachnids lend themselves well to studying complex social behaviour. "When it comes to a behaviour that any sort of animal can do, insects [and arach