VEGETARIAN DINNER: A female Bagheera kiplingi dines on a Beltian body, which she harvested from an ant-protected acacia.
Image: R. L. CURRY
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Vegetarianism is not exactly what springs to mind when considering spiders, which usually rely on web spinning and other finely tuned techniques to catch and eat other creatures. But one spider has now been observed to feed mostly on plants, shattering the common assumption that all spiders are strict carnivores.
Of the 40,000-plus spider species known, only a few nibble on plants—typically, as a dietary supplement of nectar or simply as an accidental ingestion of pollen. A new paper, published online today in Current Biology, details the natural history of Bagheera kiplingi, a jumping spider that has vegetarian leanings, and its interesting arrangement with a plant and the ants that protect it.
Certain acacia plants (Vachellia collinsii) and ants (Pseudomyrmex peperi) have developed a mutually beneficial arrangement. The plant provides hollow areas for the ants to nest, along with nutritious nuggets, called Beltian bodies, for them to eat. For their part, the ants help to fend off would-be plant eaters. The crafty B. kiplingi, however, has thwarted the system—also feasting on the plant while managing to outmaneuver attacking ants.
The spider, which lives on these acacias in Latin America, was first described in 1896 by the husband-and-wife naturalist team George and Elizabeth Peckham and named for Rudyard Kipling and the black panther character, Bagheera, in the author's 1894 Jungle Book. The fierce namesake, however, may have proved to be a misnomer for this largely herbivorous arachnid, which went scurrying about its business largely unheeded for more than a century until two researchers observed its unusual feeding habits.
The spider's strange behavior was noted independently in the field by Eric Olson, a lecturer in biology at Brandeis University, in Costa Rica in 2001 and by Christopher Meehan, then a biology master's student at Villanova University, on a field exercise in Mexico in 2007. Waking early for a field research assignment, Meehan decided to observe a jumping spider he saw on an ant-covered acacia—a type of spider that had fascinated him since boyhood.
"I was waiting, expecting it to eat an ant," says Meehan, now a doctoral candidate in the Department of Ecology & Evolutionary Biology at the University of Arizona in Tucson. But rather than nabbing an ant, he says, it struck the plant and went after a Beltian body—"it grabbed the vegetable and ran away and sat on the leaf and ate [it]. I knew it was something unique, but I'd never heard of a vegetarian spider," he says, calling the whole experience "surreal." Expecting what he had seen to be an aberration, he was surprised to witness more spiders doing the same. Once Meehan and Olson heard of each other's findings, they began collaboration on this new research.
Grabbing and eating the Beltian bodies—the spider also eats nectar and ant larvae—isn't terribly different than ingesting a more traditional piece of prey, Meehan says, but it is the digestion process that has the researchers tied up in knots. Chemical analysis of the Beltian bodies shows them to be 80 percent fiber, and "they're not by any means nutrient rich in the same sense as animal tissue," Meehan says. What might allow a formerly carnivorous animal to adapt to a mostly plant diet?
Meehan notes that the peculiar food choice may have gotten started as these arachnids fed on the ant larvae, which are, themselves, fed primarily Beltian bodies. Researchers are now looking for bacteria in these ant larvae that would help the spiders digest the plant material. They also hope to establish whether such bacteria are now passed along to spider offspring or if they must be acquired individually by eating the ant larvae.
Despite their unusual meals, these spiders still exhibit some more traditional hunting behavior. "They're like miniature cats," Meehan says. "They literally stalk and hunt the plant," perhaps lending validity to B. kiplingi's feline namesake. They also use their quick movements to evade would-be ant attackers.
The plant-based diet does, however, seem to have changed this spider's interactions with its neighbors. Individuals can live in close proximity to one another like other species of social spiders, but in other species the spiders are assumed to be cooperating in the hunt (a behavior that, researchers hypothesize, can lead to more sophisticated social organizations). But in the case of B. kiplingi, in which food is simply harvested from the plant, no cooperation is needed, raising the question of why they live in such close quarters. Meehan proposes that the social behavior might be "to reduce local resource competition and reduce aggression," which would be important in instances where some plants are covered with thousands of these spiders.
As for the plants that the spiders feed on, most don't appear to be under severe stress by the arachnid attacks. Some acacias in Mexico, however, that have heavier loads of spiders might be suffering from decreased ant protection, Meehan notes. With all of those spiders harvesting the Beltian bodies for themselves, there are fewer for the ant larvae and thus fewer ants. This sort of instance raises questions about stabilization of the spider–plant–ant system. "Instead of eating the resource once-removed," like the ants, Meehan says, the spiders "go straight to the source." The eating pattern allows more spiders to subsist on a plant than otherwise could get by eating the ant larvae directly.
Regardless of how these spiders came to be primarily plant-eaters, their continued study will likely illuminate a rare species—one that Meehan calls "more extraordinary than a flying pig"—and the system the produced them. "Co-evolution can have cascading effects," Meehan says. "It can serve as evolutionary stepping-stones for third parties that intercept them." And for this oddly adapted spider, it appears to have been a boon.
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8 Comments
Add CommentThe title to this article represents exactly how low this publication, indeed all of American science education has sunk.
Reply | Report Abuse | Link to thisIn what way is a plant not alive?
This headline is a perfect example of how low this publication, indeed American science education in general, has sunk.
Reply | Report Abuse | Link to thisIn what way are plants not "alive"?
Plants are indeed a life form. The use of the word "prey," by any dictionary definition, either specifically refers to prey as animal in nature, or connotes as such. I fail to understand your reference to "how low" Scientific American and "science education in general has sunk." Science, the biology facet in particular, is forever changing the usage and form of its own language to meet the criteria of newly found information as well constantly evolving theory ... I have been in the research and educational field for the number of years needed to have learned as well as to have accepted the morphing of vocabulary. The word "prey," however, has never been part and parcel to this change.
Reply | Report Abuse | Link to thisHow very sad that you have had to nitpick and detract from a very intriguing article by Ms. Harmon. My congratulations go to the author and to the magazine that has always been revered in the circle of scientific publications.
Stone- While the Sci-Am articles generally could stand to be a bit more scientifically rigorous, the article here is good enough for this non-expert. Furthermore, I am quite sure that Ms. Harmon knows acacia trees are organisms. Beltian bodies, however, are only pieces of an organism. (Besides, the word 'live' here obviously means 'animate'. )
Reply | Report Abuse | Link to this"Herbivory in a spider through exploitation of an ant–plant mutualism"
http://www.cell.com/current-biology/abstract/S0960-9822(09)01626-1
http://uanews.org/node/27932
Few would argue that "Live prey" refers to anything but a living animal, so I have no idea what untrue or unseemly message can be found in the title. At first I did think it refered to carrion or scavanged animal remains, however, it was a delightful surprise to find out this spider had vegetarian habits. It was a great article.
Reply | Report Abuse | Link to thisThis is a species of arachnid that is an omnivore.
Reply | Report Abuse | Link to thisMost spiders live by sucking the juices/"blood" of its prey.
right?
Arachnids normally immobilise a live prey, and then dessicate them.
The interesting, and biological advancement is the intelligent leap to a different food source.
That Costa Rica has some of these spiders is no surprise.
It is one of the last natural laboratories left.
I just wish they would fix this double posting problem...
Reply | Report Abuse | Link to thisGreat article! It's fascinating to think a spider might be able to subsist on plant material. I would really like to know if the spider can live on a 100% vegetable diet.
I found this to be quite an interesting article.
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