Big brothers and sisters pay off for nature's social spiders

The researchers found 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. The study, published online in the journal Animal Behavior, describes how prey sharing can directly benefit spiders living as a group. Australian social huntsman spiders (Delena cancerides) are fairly common throughout the southern half of Australia, living as family groups with a single mother and multiple clutches of her offspring in retreats under the loose bark of dead trees.

"One of the most unusual things about Delena colonies is that there are siblings of a huge range of ages and sizes, in the colonies together at the same time," said Linda Rayor, a Cornell entomologist and co-author of the study. "It's common to have tiny spiderlings mingling with older siblings that are almost a year old. So what is totally cool about Delena is that mix of siblings of different ages and how they interact around prey brought into their retreat." Rayor describes such social sharing in a Cornell video.

"If you are small, the number of things you can capture may be quite limited," said Eric Yip, the paper's lead author who conducted the research while a graduate student in Rayor's lab.

"The concessions that an essentially solitary hunter like a spider makes in order to live in groups I think is really interesting," Rayor said. "What we're seeing is these huntsman spiders, by living in groups, end up having many benefits in many ways."

The study was funded by the National Science Foundation, Australian-American Fulbright Commission and the President's Council of Cornell Women.

Video: video/preying-together-older-siblings-aid-younger-social-spiders" href="http://www.cornell.edu/video/preying-together-older-siblings-aid-younger-social-spiders">www.cornell.edu/video/preying-together-older-siblings-aid-younger-social-spiders