A spider goes vegetarian

Written by Thomas Hesselberg

Tuesday, 13 October 2009

An ant-acacia Acacia collinsii like the one on which the vegetarian jumping spiders were found. Photo taken by Thomas Hesselberg.

Whether using a web or hunting actively, all spiders are lethal killing machines if you happen to be a hapless insect. Well at least that was what we believed until recently. In the latest issue of Current Biology scientists from USA and Canada have found a vegetarian spider.

The spider belongs to the group of jumping spiders, which are usually active hunters without a web. They have a good vision and use it stalk prey at a distance before they are within jumping distance. However, this particular jumping spider does not hunt any prey, but spend its life on a plant. Not just some plant though, but an ant-acacia, which is a plant that lives in a close mutualism with an ant. The acacia offers the ants housing in its thorns and food in the form of special fat and protein rich Beltian bodies and in return the ants protects the plant against herbivores and other encroaching plants.

The jumping spider, however, takes advantage of this system. Its good vision and quick feet allows it to avoid the aggressive ants and steal the Beltian bodies in front of them. The scientist studied the actual behaviour of more than 1,000 of these spiders in both Mexico and Costa Rica and observed them to almost exclusively feed on Beltian bodies while also occasionally enjoying an ant larva snack. They also analysed the stomach content of 50 Mexican spiders and showed that around 90% of it came from Beltian bodies. It, therefore, seems than no other conclusion can be reached than that these spiders do indeed belong to the first described predominantly vegetarian spider species.

However, the question still remains of how the spider has managed to change its digestive system to be able to cope with solid plant material, while all other spiders only can digest liquefied insect and other animal remains.

Source
Meehan, C. J., Olson, E. J., Reudink, M. W., Kyser, T. K. and Curry, R. L. (2009) Herbivory in a spider through exploitation of an ant-plant mutualism. Current Biology 19, R892-R893.

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