I can't help but post this: ∃ vegetarian spiders!

Wired News: Kinder, Gentler Spider Eats Veggies, Cares for Kids

Each of the world’s 40,000 spider species survives by hunting and killing — except, that is, for Bagheera kiplingi, the world’s first vegetarian arachnid.

Found in Central America, the order-defying jumping spider eats nutrient-rich structures called Beltian bodies, which are found on the tips of Acacia trees. Trees produce the bodies to feed ants that defend them, which is a textbook example of what’s called co-evolutionary mutalism, and one that B. kiplingi has evolved to exploit.

In a paper published Monday in Current Biology, researchers describe the spider’s ant-evading habits and provide a molecular analysis of its body composition, proving that B. kiplingi is indeed what it eats: plants, with a few larval ants on the side. (After all, 400 million years of evolutionary habits die hard.)

A few other spiders have been documented consuming nectar, but only as a snack. No other spider is so predominantly vegetarian. And that’s not all: It looks like B. kiplingi males help care for eggs and young — something entirely unprecedented in the spider world.

The researchers are now studying whether there’s a link between B. kiplingi’s predilection for plants and parental concern. Maybe going veggie softened its heart.

Image: Current Biology

Citation: “Herbivory in a spider through exploitation of an ant-plant mutualism.” By Christopher J. Meehan, Eric J. Olson, Matthew W. Reudink, T. Kurt Kyser, and Robert L. Curry. Current Biology, Vol. 19, Issue 19, October 13, 2009.