It isn't entirely clear why B. kiplingi is able to evade acacia ants, whose goal is to protect the shrub from attacks.
Credit: Robert L. Curry
NEW YORK: A jumping spider found in Central America is the first known spider species to subsist primarily on plants, according to American scientists.
While many spiders eat nectar and a single species has been observed eating pollen in addition to insects, Bagheera kiplingi dines almost exclusively on 'Beltian bodies', protein- and lipid-rich structures located on the tips of acacia shrub leaves.
Out of about 41,000 known species it is the sole spider to maintain a nearly vegetarian diet.
Mistaken for an ant
Acacia is well known amongst scientists for its symbiotic relationship with ants: the animals eat the acacia's sap in return for protection against herbivores and competing plants. But, despite many studies on this phenomenon, B. kiplingi's veggie tendencies went largely unnoticed.
"People weren't looking with an unbiased eye. Some scientists have even misidentified the spider as an ant and never noticed the phenomenon of its diet," said Mark Meehan, lead author of a paper describing the spider today in the journal Current Biology.
Meehan is based at the University of Arizona in Tucson, USA. He made the discovery while doing field research in Quintana Roo on Mexico's eastern coast last year. Similar behaviour was independently recorded by co-author Eric Olsen of Brandeis University in Waltham, USA, while working in the field in northwestern Costa Rica.
Chemical mimicry
Click here to see a video of the spider harvesting a Beltian body.
To confirm their observations of the spider's diet, the team performed stable isotope analysis on its body tissues. Using this kind of analysis, the ratios of isotopes of nitrogen and carbon are used to determine what types of food an organism eats. The nitrogen ratio shows whether it consumes plants or animals, and the carbon ratio hones in on the specific food source.
The biomass of both Mexican and Costa Rican spiders were compared to that of the acacia ants and larvae, Beltian bodies and closely related spider species. Nitrogen ratios showed that B. kiplingi eats far more plant matter than related species.
Carbon ratios point to Beltian bodies as their favourite snack, making up 60 and 90% of the Costa Rican and Mexican species' diets, respectively.
"Spiders are generalist predators, so you would have to watch for a fair period of time [to confirm their plant-based diet percentage]," said Norman Platnick, curator of spiders at the American Museum of Natural History in New York City. "But, if the data supports the finding, then there is no question this is a new and significant discovery," he said.
It isn't entirely clear why B. kiplingi is able to evade the acacia ants, whose goal is to protect the shrub from attacks. One possible solution is that the spiders use their physical abilities to jump out of reach of danger.
Meehan thinks that the spiders may also mimic the ants' chemical scents in order to blend in; and this is currently being investigated. Meehan and his team plan to confirm the chemical mimicry and explore how it might shape the population structure and social evolution of these spiders.
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