by Joseph DeSisto
Meet Furcula borealis, the caterpillar of the white furcula moth:
It’s a weird-looking caterpillar already, but even weirder when viewed head-on:
Like all insects, caterpillars have only six legs, and these are located near the front of the body, just behind the head. The sticky, climbing appendages along the rest of the trunk are not true legs but “prolegs,” which are lost during metamorphosis. In Furcula caterpillars (and the related Cerura, shown below), the last pair of prolegs are modified into long, rigid “tails.”
The furcula moths belong to the strange and beautiful family Notodontidae. These are sometimes called prominent moths, despite mostly being brown, gray, or some combination thereof. Recall, however, that in my last post about caterpillars I referred to notodontid caterpillars as the dragon caterpillars. Furcula, then, are unofficially dubbed the fork-tailed dragon caterpillars.
In case you’re wondering what F. borealis looks like as a moth, here’s an example specimen:
So what is the forked tail for? To find out, we simply tap our little dragon on the head. This is what happens:
Bright red tentacles begin to emerge from the modified prolegs. In less than a second they are fully everted:
The fork-tailed dragon then waves these tentacles about, and even attempts to rub them onto the offending party (i.e., my finger). The “strike” reminds me of a scorpion trying to sting, if scorpions dressed up as clowns and went to birthday parties. After tapping me, the tentacles disappear as quickly as they emerged, while the caterpillar tucks its head and braces itself for another attack.
In a less dramatic fashion, many insects use eversible organs to rub toxins on their predators. Rove beetles are an example — this explains the way many of them run, with abdomens held high in the air like scorpions. If you grab one, it will use its flexible abdomen to rub a cocktail of nasty chemicals on you, some of which can cause blistering. But in Furcula and Cerura caterpillars, the tentacle-rubbing is actually a harmless show designed to scare off predators. I must admit, were I a foraging bird, I would think twice about attacking a caterpillar with such a bizarre and intimidating display.
And yet, in an ironic twist, these caterpillars are not harmless. If sufficiently disturbed, they can fire off a burst of formic acid — the stuff fire ants sting you with — from glands behind the head. In F. borealis, these are stored in spiky, poisonous-looking projections:
Don’t mess with the fork-tailed dragons!