LINDA RAYOR: This is Delena cancerides. This is an Australian Huntsman spider. It's considered to be a relatively common spider. But they're very, very patchily distributed, especially in the southern half of Australia. They are primarily found underneath the bark of dead trees, especially acacia trees.
And the Huntsman spiders, they don't have webs. They're not capturing prey using silk. They're hunters and will either stand and wait to grab prey or they will chase after it. But essentially, they're not relying on silk webs. And so this is really, really unusual.
What you've got in this colony is you've got a situation where you've got one adult female. You never have more than one adult female breeding. And then you've got multiple clutches of her youngsters. Essentially, what we've been interested in are the costs and benefits of group living in an unusual social spider.
So Eric Yip just finished his PhD at Cornell University, did a spectacular PhD research, and he spent lots of time in Australia tracking these animals late at night. And what he found is that, one, is that they're hunting on their own and that they would really rather not share their prey with anybody else.
And so almost all prey capture happens away from their retreat. But at the same time, when you brings the bark retreat off, there's silk at the bottom with bunches of prey. So there's little mittens of prey at the bottom. It's clear that at least some prey is getting into the retreat and is being eaten. Now I know from lab studies that on the order of 30% of the prey is shared.
As Eric was doing these analysis, what became very, very clear is if you are a little spider, say, fourth or fifth in start, if you've got older siblings, you get way better food. They're in way better condition. They're heavier. They're on the order of 6% to 7% heavier than their siblings without older siblings.
But almost as important, there are no costs to having younger siblings surviving. There just aren't that many issues for these animals. What's happening here is you've got one of the sub-adult animals in the group has captured a cricket, and different siblings are trying to get in there and convince it to let them have a bite of the prey. So they're trying to get in and share the prey with the spider.
Animals that have been able to figure out how to live together, like these two siblings here that are sharing prey, it's payoffs. There are all sorts of advantages layered on, that they grow faster, they are healthier, they have better survival, they're bigger at the point where they're sharing prey.
So there's lots and lots of benefits to group living if you can overcome the costs. And so to me, that's the really interesting part. Given the concessions that we as humans need to live together in groups, it's interesting how different animal groups have done it.
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Cornell researchers studying Australian social huntsman spiders have discovered that younger siblings thrive when raised in nests with older siblings. Bigger brothers and sisters capture bigger, juicier prey, which they - at least occasionally - share with their younger siblings.
Through field data and laboratory experiments, the researchers showed that younger siblings weighed substantially more when they shared the prey of their elder brethren. Since smaller spiders eat relatively little, there is little to no cost to the older siblings. And healthier family groups help carry on that family's genes.
A study by Eric Yip and Linda Rayor, published in the journal Animal Behavior, describes how prey sharing can directly benefit spiders living as a group.