To save the web, it pays to be aggressive (Image: Jonathan Pruitt)

On the ecological battlefield, friendly spiders are the first to fall. A new study shows that the behaviour of individual animals can determine the fate of entire communities.

Most spiders are loners, but Anelosimus studiosus lives in forests of the Americas in colonies of up to 200 related individuals that build communal webs called silken reefs.

The reefs attract other spider species and some steal food and even prey on Anelosimus. As a result, the colony usually collapses within a few years.


But occasionally, the reef lasts longer, growing to several times the size of a large car and containing more than 50 spider species, says Jonathan Pruitt, an ecologist at the University of Pittsburgh, Pennsylvania.

Earlier, Pruitt and his team had shown that individual Anelosimus spiders have genetically determined “personalities”. Some are aggressive, others more docile. Could these traits affect the fate of the colony?

To find out, they created 30 lab colonies, starting with two docile or two aggressive spiders, and transferred them to a Tennessee forest, where they tracked them for seven years.

Colonies founded by docile spiders quickly accumulated other spider species, including some that harmed the colony. By contrast, colonies founded by aggressive spiders were better able to fend off other species at first. “Eventually, they all succumb, but aggressives certainly make it for longer,” says Pruitt.

The results sound a cautionary note for ecologists hoping to predict the fate of communities, says Daniel Bolnick at the University of Texas in Austin. “Individuals vary, and that matters in all sorts of ways for community ecology.”

Journal reference: Journal of Animal Ecology, doi.org/5bt