The Doctor Weighs In

By Dov Michaeli MD, Ph.D

Go to the ant, you sluggard; consider its ways and be wise!

King Solomon, Proverbs 6:6

An item in the October 12 issue of Current Biology is really cool. Scientists from the University of Arizona and Brandeis University described the first known vegetarian spider. In fact, the aforementioned creature has gone a step further: he is a vegan, eating only uncooked veggies. They discovered this species (B.kiplingi) in Mexico and Costa Rica. But that's not all - the story gets even more interesting.

The Evolution of Vegetarianism

Spiders normally spin webs to better catch unwary insects for their daily “bread”. But this spider had a great insight: acacia plants are normally swarming with ants; this is a well-known example of mutualism — the insects provide protection for the plant and in return the acacia produces nutritious leaf tips (Beltian bodies, for the more scientifically inclined) for the ants to eat. So what does our clever spider do? He learned to jump to avoid the ants, and when the opportunity presents itself –he feeds on those very nutritious leaf tips. Speaking of rigorous science, the authors documented that this is indeed the major nutritional source of this veggie-spider by analyzing the chemical composition of its body, and demonstrating that its source is none other than those Beltian bodies.

And now for the final surprise: the males of B.kiplingi take care and protect its young larval offspring, a phenomenon unheard of in the spider world.

More Questions

Like every good piece of research, this one raises more questions than answers. Here are a few:

1. How did this adaptation occur? Enzymes required to digest an insect meal are quite different form the ones required for digesting plant material. Obviously, mutations had to occur. Did they change the function of pre-existing digestive enzymes, or did they occur in non-digestive proteins acquiring the function of plant-digesting enzymes?If it turns out to be the latter it would be absolutely astounding. But I wouldn't dismiss anything concocted by this non-conformist spider.
2. Is there a functional relationship between the unconventional diet and the equally unconventional behavioral change of rearing the young? Did one inevitably lead to the other? And if so, what came first, the diet or the “socially conscious” behavior?
3. Finally, like everything else nowadays, we should consider the profound political implications. Numerous studies have demonstrated that liberals are more likely than conservatives to be vegeterians, while conservatives are more prone to feast on red meat. Furthermore, progressive fathers assume more responsibility in performing child rearing and other domestic duties. And finally, a respectable poll showed that more educated people tend to vote Democratic rather than Republican. Caveat: these are only "tendencies", not absolute distinctions. Having said that, is it possible that the political equivalent of "women are from Venus, men are from Mars" is "progressives eat veggies, conservatives eat bugs"?

I think I’d better quit now before I incur the wrath some fire-breathing, flesh-eating commentators.