“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 Christopher Meehan from Villanova University.

About the size of a person's pinky nail, B. Kiplingi feeds on the acacia plant. It uses hunting strategies to get past ants guarding the acacias  from other herbivores.  In return, the guard ants get a comfy place to live in the plant’s hollow spines while it eats acacia nectar and the shrubs' leaftips.

B. Kiplingi spends its entire life on the acacia shrubs, so guard ants are always a threat. When hunting, B.K.  changes targets when approached by an ant and uses silk droplines as retreat ladders. The spiders usually nest on the ends of older acacia leaves, the areas least patrolled by the ants.

“Most of the big spider textbooks almost outright claimed there are no herbivorous spiders,” Meehan says. “It’s on par with the flying pig in terms of novelty.”

Direct observation, video recordings and chemical analyses of such spiders suggest the animals get most of their food from plants. In the Mexican population, about 90% of the spiders’ diet came from plant tissue, with the rest made up of ant larvae, nectar and other items.

In Costa Rica, where a B. Kiplingi. "cousin" lives, the spiders got about 60% of their diet from acacia plant tissues.

When the spiders do hunt ant larvae, they mimic the ants’ behaviors, for instance by making jerky movements, to get to the food.