How social huntsman spiders live and hunt together
Most spiders are web-building, solitary creatures. So the social huntsman spiders, which live in webless "retreats" with hundreds of other spiders, are very unusual.
Now, a detailed study of this spider species, Delena cancerides, has revealed exactly how the huntsman work together.
Not only do large "mother spiders" defend the colony from invading predators, but spiders occassionally bring spoils back from a hunt for other spiders to share.
The spiders are native to Australia, where they make their homes beneath the bark of trees.
Eric Yip from Cornell University in Ithaca, New York, US who led the study, created windows into the spiders' retreats, replacing sections of bark with transparent plastic. The spiders are most active at night, and Dr Yip spent 68 nights watching the spiders from dusk until dawn.
"I spent hundreds of hours looking through a hole in the bark of a tree using a voice recorder to document their behaviour," he explained to BBC Nature.
He found that, when a potential predator such as another spider or an ant, came into the retreat, the mother spider would attack it.
"Mom was very protective of her brood," said Dr Yip, "And she was usually able to defeat most predators."
"She doesn't seem to go out and forage very often; she seemed to stay [in the retreat] as much as she could. So there's clearly a big advantage to maternal care in these spiders."
Dr Yip also attempted to follow the spiders when they left the retreats.
- There are 60 known species of group-living spider and 42,000 different spider species in the world
- Most social spiders build webs, which they live on in groups. One well-studied species, Anelosimus eximius, spins webs that stretch for several metres and contain over 10,000 spiders
"A lot of people assumed they didn't hunt together and that they just ate what came into the retreat," said Dr Yip.
"But if they're hungry they will go out and find food."
Like most other spiders, when these foragers found food they would eat it, rather than return it to the colony to share their meal.
"But if it started to get light [while they were] out, they would take whatever they were eating back to the retreat and share it," Dr Yip explained.
"They have to go back so they're not exposed to predators in the daylight."
Dr Yip and his Cornell colleague, Dr Linda Rayor, are planning to continue their studies of these strangely social spiders to find out why they live and work together.
"We're social animals, so we assume that living in groups is beneficial," said Dr Yip.
"But if you look closely, there's a real cost in living closely with your competitors, particularly for spiders."
"Most of them are cannibalistic, so a bigger spider not eating a little spider is a cost- it's an easy meal."
"They're doing things very differently to other spiders."