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Bagheera kiplingi has a most un-spider-like adaptation: a taste for plants.

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Meehan, C. J., Olson, E. J., Reudink, M. W., Kyser, T. K., & Curry, R. L. (2009). Herbivory in a spider through exploitation of an ant–plant mutualism. Current biology, 19(19), R892-R893.
Scully, E. J. (2012). Nesting ecology of the herbivorous ant-acacia jumping spider, Bagheera kiplingi. Villanova University.
Jackson, D. E. (2009). Nutritional ecology: a first vegetarian spider. Current Biology, 19(19), R894-R895.
Peckham, G. W., & Peckham, E. G. (1896). Spiders of the family Attidae from Central America and Mexico. Natural History Society of Wisconsin. (pg.94)
Once upon a time, there was a little brown and green spider and its name was Bagheera kiplingi, and it lived in Mexico and Central America.

And it wasn’t like all the other spiders. Now, there are more than 45,000 species of spiders alive today.

They range from smaller than the head of a pin to roughly dinner plate-sized, but they all share something in common - they’re predators. But little Bagheera kiplingi wasn’t interested in snacking on insects and other arthropods. At least, not all the time.

Instead of spinning webs or waiting to ambush prey, it opted for a diet that’s mostly made up of plant-foods. And for a spider, that makes it one bizarre beast. [ ♪ Intro ] Okay, I know that “vegetarian” spider sounds like the main character of a children’s book about the importance of being yourself, but Bagheera kiplingi doesn’t come from a fairy tale. And, yes, its genus is named for the black panther character in the Jungle Book and its species for that book’s author, really driving the children’s literature theme home.

But it’s a real spider! It’s a member of the family of jumping spiders, along with other photogenic arachnids like peacock spiders. And it’s the only spider we know of, the only one in 45,000, with a mostly herbivorous diet.

See, B. kiplingi lives on a certain kind of thorn-tree that produces specialized leaf tip structures called Beltian bodies. These Beltian bodies are high in protein and sugar. Tasty!

But they’re also high in fiber, which is less ideal for spiders, and we’re still not sure how they break down solid plant material for digestion. Along with consuming their Beltian bodies, B. kiplingi sips the nectar of these trees, which isn’t actually produced by its flowers, but by special glands, instead. Which all sounds really nice and very un-spider-like.

But, there’s a catch, or two, that makes this whole thing a little less heartwarming. The first one is pretty minor and it’s just that B. kiplingi isn’t the strictest vegetarian in the world. Don’t get me wrong, it’s definitely primarily herbivorous.

Lab tests confirmed that the carbon and nitrogen isotope signatures in its tissues match what you’d expect for a spider that eats plants. But scientists have studied two populations of this spider, one in Mexico and one in Costa Rica, and found that the percent of their diet made up of plant foods differs between the two groups. In Mexico, Beltian bodies make up 91% of the items consumed by the spiders, with another 5 or so percent of their diet coming from nectar.

In Costa Rica, the split is more like, 60% Beltian bodies and 20% nectar. And the rest? Nectar-eating flies, occasionally other, smaller members of their own species, yikes, and ant larvae.

Which brings me to the second catch. The reason there’s ant larvae around for B. kiplingi to eat is because the thorn-trees the spiders live on have co-evolved a mutualistic relationship with several species of ants in the genus Pseudomyrmex. In exchange for shelter in their hollow thorns and food, the ants provide the trees with protection from herbivores, or, at least, they try to.

If you were asking yourself why a plant would make tasty balls of protein and sugar at the end of their leaf tips, good work, now you’re thinking like an evolutionary biologist. Plants don’t just shove a bunch of energy into a bag because they want to convince spiders to leave their murderous ways behind them. The Beltian bodies that B. kiplingi eats are actually supposed to be food for these ants.

This keeps the ants around, and the ants protect the whole plant, not just the Beltian bodies, from getting gnawed on by other insects. Basically, the spider is cheating this beautiful system that evolved between the ants and the thorn-trees. But without that relationship, B. kiplingi wouldn’t have become herbivorous.

As for how the spider started consuming Beltian bodies in the first place, the researchers who studied it suggested it might come from them originally eating other resources that didn’t run away, things like ant larvae and insect eggs. If you’re not going to chase down prey anyway, the way most jumping spiders do, you might as well go for food that’s always available, like plants! And the evolution of herbivory had another interesting consequence for B. kiplingi, one that might help restore some of the fairy tale feel to this little arachnid.

It’s friendly! Well, friendly for a spider. Most spiders are solitary, territorial, and aggressive toward other spiders, including members of their own species.

There are only a few species that are willing to put up with company. But researchers have observed hundreds of B. kiplingi individuals living on the same tree! And this might be possible because they aren’t competing for resources, there are enough Beltian bodies to go around.

Now, these spiders don’t seem to cooperate on the scale of ants or bees, or even of truly social spiders, which capture prey using communal webs. But they do have some things in common with social spiders, like females outnumber males two-to-one, and one researcher observed females guarding their young in nests. So, B. kiplingi has been called “quasi-social” by some scientists.

B. kiplingi, at the very least, tolerates being around other members of their species. Except for sometimes when they eat them. And who knows what future studies of this little spider might discover, while the species was named in 1896, researchers only noticed their odd food preferences in 2001!

And that’s the story of Bagheera kiplingi. It lived happily ever after, putting up with the other members of its species and snacking on bits of the thorn-tree. So, I guess, the moral of the story is to just be yourself!

Even if that makes you a bizarre beast. The Bizarre Beasts pin club subscription window is open RIGHT NOW through the end of February 7th. This month’s pin is fabulous and very shiny, really, a high-quality spider.

Sign up now to get your own B. kiplingi in the middle of the month and the pins after that around the time each new video goes live. And we’ll be posting even more tasty bits about this spider on Twitter @BizarreBeasts, and on Instagram and Facebook @BizarreBeastsShow! If you’ve made it this far, you probably already know this, but profits from the pin club go to support our community’s efforts to decrease maternal mortality in Sierra Leone. [ ♪ Outro ]