The World's First Known Mainly Vegetarian Spider

The tiny Bagheera kiplingi is somewhat of an oddity in the insect world. This pinky-size spider is the only known spider to have a mainly vegetarian diet.

The spider, found in Central America, is the only species out of approximately 40,000 that is not strictly a predator. They live their lives on acacia plants nibbling the tender young shoots; raising their young on the ends of old leaves where guard ants protecting their acacias from other herbivores don’t patrol; and, avoiding the ants that would run them off.

“This is really the first spider known to specifically 'hunt' plants; it is also the first known to go after plants as a primary food source," said study researcher Christopher Meehan of Villanova University in Pennsylvania.

This uneasy relationship between the spiders and the ants provide both with a reasonably comfortable lifestyle – the plant’s hollow spines provide a homestead and they are provided with acacia nectar and juicy leaf tips to sustain them.

Scientists have found a type of jumping spider (adult female, shown here) dines primarily on leaf-tips from an acacia plant (yellow-orange leaf held by spider). Credit: R. L. Curry.

Since B. kiplingi spends its entire life on the acacia shrubs, they must avoid the ants at all times. When hunting, they actively avoid the ants using a variety of tricks. One of which is to use their silk not for webs; but, as droplines or retreat ladders.

"Most of the big spider textbooks almost outright claimed there are no herbivorous spiders," Meehan told LiveScience. "It's on par with the flying pig in terms of novelty."

The vegetarian jumping spider, called Bagheera kiplingi, nests in acacia plants that are guarded by ants. Here, a female spider guards her nest from one such ant. Credit: R. L. Curry.

The plant-eating strategy seems to be successful. Direct observation, video recordings and chemical analyses of these spiders in Mexico and Costa Rica suggest the animals get most of their food from such plants.

In the Mexican population, about 90 percent of the spiders' diet came from plant tissue, with the rest made up of ant larvae, nectar and other items. In Costa Rica, the spiders got about 60 percent of their diet from acacia plant tissues.

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