There are approximately 40,000 species of spiders in the world, all of which have been thought to be strict predators that feed on insects or other animals. Now, scientists have found that a small Central American jumping spider has a uniquely different diet: the species Bagheera kiplingi feeds predominantly on plant food.
The research, led by Christopher Meehan of Villanova University and Eric Olson of Brandeis University, has revealed the extraordinary ecology and behavior in Bagheera kiplingi, which lives throughout much of Central America and southern Mexico. There, the spider inhabits several species of acacia shrubs involved in a co-evolutionary mutualism with certain ants that has long been a staple of ecology textbooks: the ants fiercely guard the plants against most would-be herbivores, while the acacias provide both housing for the ants via swollen, hollow spines and food in the form of nectar (excreted from glands at the base of each leaf) and specialized leaf tips known as Beltian bodies. The Bagheera spiders are "cheaters" in the ant-acacia system, stealing and eating both nectar and—most remarkably—Beltian bodies without helping to defend the plant. The spiders get the job done through active avoidance of patrolling acacia-ants, relying on excellent eyesight, agility, and cognitive skills.
The research will appear in the October 13 issue of Current Biology, accompanied by a Dispatch article highlighting the study’s importance.
Co-author Olson first discovered herbivory by the spiders in Costa Rica in 2001. In 2007, Meehan independently observed the same behaviors in a spider population in coastal Quintana Roo, south of Cancún, Mexico, during a field project for a Tropical Biology course taught by Villanova professor and study co-author Robert Curry. The two research groups subsequently combined efforts to jointly publish the discovery. The research also formed the basis of Meehan's Masters degree from Villanova, completed in 2009.
In the field, the researchers documented behavioral patterns through direct observations and high-definition video recordings. Herbivory was especially clear in the Mexican population: Beltian bodies accounted for more than 90% of 140 food items identified. According to Meehan, "This is the first spider in the world known to deliberately ‘hunt’ plant parts; it is also the first found to go after plants as a primary food source." Spiders in Costa Rica more frequently supplemented plant food with animal prey items, including ant larvae.