Not Exactly Rocket Science

In Latin America, there lives a unique spider called Bagheera kiplingi. It’s a jumping spider and it shares the group’s large, acute eyes and prodigious leaping ability. But it also has a trait that singles it out among all 40,000 species of spider – it’s mostly vegetarian.

Virtually all spiders are predators. They may hunt using different methods but they all end up sucking the liquidised innards of their prey. If they consume plants, they do so rarely, even accidentally. Some take the odd sip of nectar to supplement their diet of flesh. Others accidentally swallow pollen while recycling the silk of their webs.

But B.kiplingi is an exception. Christopher Meehan from Villanova University has found that this spider exploits a partnership forged between ants and acacia trees. The trees employ ants as bodyguards and it pays them with shelter inside hollow thorns, and nutritious nodules called “Beltian bodies” that grow from its leaves. B.kiplingi has learned to steal these delicacies from the ants, and in doing so, it has become the world’s only (mostly) vegetarian spider.

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Meehan spent seven years observing the spider and filming its foraging trips. He showed that the spiders are almost always found on acacia trees that are occupied by ants, for the trees only grow the tasty Beltian bodies when ants are around. In Mexico, Beltian bodies make up 91% of the spider’s diet, while in Costa Rica, they make up 60% of it. More rarely, they will also drink nectar and evern more rarely, they will have a meat treat by taking ant larvae, flies and even others of their own kind.

Meehan confirmed his results by analysing the chemical make-up of the spiders’ bodies. He looked at the ratio of two types of nitrogen: N-15 and N-14. Plant-eaters tend to have relatively less N-15 than meat-eaters do, and sure enough, B.kiplingi‘s body had 5% less of this isotope than other species of jumping spiders. Meehan also considered the ratio of two carbon isotopes, C-13 and C-12. Meehan found that the vegetarian spider and the Beltian bodies had virtually identical ratios, as is usually the case between an animal and its food.

Feeding on Beltian bodies is worthwhile but far from straightforward. First, there’s the problem of the bodyguarding ants. B.kiplingi‘s strategy is stealth and evasion. It builds its nests at the tips of the oldest leaves, where ants rarely patrol. They will actively avoid ant guards if they see them approaching. If cornered, they will use their powerful legs to leap away. Sometimes, they even drop to safety using a line of silk, hanging in midair until the danger passes. Meehan documented several different strategies, all evidence of the impressive mental skills that jumping spiders are known for.

Even if it avoids the sentries, B.kiplingi has another problem. Beltian bodies are extremely high in fibre and spiders really shouldn’t be able to handle that. Spiders can’t chew their food; they rely on digesting their prey outside their own bodies using venom and digestive juices, and ‘drinking’ the liquefied remains. Plant fibre is a much tougher mouthful and we still don’t know how B.kiplingi copes with it.

Even so, it’s clear that the rewards are worth it. Beltian bodies are a ready-made source of food that’s available all year round. By exploiting this feast that’s produced for others, B.kiplingi has become very successful. Today, it’s found throughout Latin American, wherever ants form partnerships with acacias.

Reference: Current Biology in press

More on spiders:

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Comments

  1. #1 Zach Miller
    October 12, 2009

    Wierd! I’ve always thought jumping spiders would be the best “pet” spider you could have, and this particular species wouldn’t try to kill me!

  2. #2 TR Gregory
    October 12, 2009

    Guess what I will be adding to my lecture on co-evolution in the bit about ants and acacia trees….

  3. #3 David
    October 12, 2009

    and the Müllerian bodies found on myrmecophytic Cecropiaceae, TR…

    and the cleptobiotic social wasps (Charterginus ssp.) that steal from ants associated with myrmecophytes…

    [Ed, I wish there was a way to publish this on my Facebook page]

  4. #4 David
    October 12, 2009

    Re. Facebook…

    LOL, never mind Ed, my bad… or rather that of my laptop- the “share” array was missing the first time around!

  5. #5 Lilian Nattel
    October 12, 2009

    That’s fascinating. But I’m glad we have carnivorous spiders in our house…we count on them to get rid of other insects. Though I have to say that as a vegetarian myself those jumping spiders have a special place in my heart.

  6. #6 Ed Yong
    October 12, 2009

    Hear hear for friendly insectivores. I have a strong suspicion (based on a lack of bites, nocturnal squeaking and bathtub droppings) that our safari lodge room had a guardian bat that was hawking all the mozzies at night…

  7. #7 Captain Skellett
    October 12, 2009

    Where do you find this stuff?

    There’s a gigantasauric huntsmen perched in the corridor linking the offices to the kitchen today. Wish IT was a vegetarian.

  8. #8 IanW
    October 13, 2009

    The bare necessities, the simple bare necessities, forget about your troubles and your strife…!

  9. #9 Priyank Chandra
    October 13, 2009

    What caught my attention was the name.
    Bagheera Kiplingi? An obvious ode to the Jungle Book, by Kipling. Could it also be because Bagheera in Jungle Book was never shown to ever hunt (or did he?)?

  10. #10 Mal Adapted
    October 13, 2009

    At the beginning of The Jungle Book, Bagheera killed the bull that bought Mowgli from Shere Khan, thus saving Mowgli’s life.

  11. #11 Chrystal K.
    October 13, 2009

    That’s not so hard to believe for those of us that don’t study science.

  12. #12 Austin
    October 13, 2009

    It would be cool if there was a link between the rare consumption of ant larvae and the ability to digest plant fibers (some kind of uptake of useful microorganisms?)

  13. #13 Cold Storage
    October 28, 2009

    IT was a vegetarian.

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