Monday, April 24, 2017

The Life History of the White Furcula

It's probably not an exaggeration to say that the majority of meat-eating animals (taking into account, not just tigers and lions, but all the parasitic wasps, birds, spiders, parasitic flies, and so on) feed primarily on caterpillars. The caterpillars didn't get a vote in this, so they have concentrated on creating millions of ploys to avoid being eaten.

For instance, some caterpillars have learned how to eat poisonous plants without themselves being poisoned. Instead they sequester the poison in their tissues, so that whatever creature tries to eat them will be poisoned. Others have venomous hairs or spines on their backs so that whatever creature mishandles them will be stung and even killed. Other caterpillars look exactly like a gooey revolting bird dropping which no one is interested in eating. Or they might get two large false eyes on their back and look so much like a snake head that a bird that suddenly spots one nearby in the leaves will fly off in fright. The commonest, of course, is just to look so much like the leaf they are sitting on that they become invisible.

Well, those are all familiar ploys. The caterpillar of the White Furcula moth provides some new ones.

First, let's straighten out some anatomical matters. A moth caterpillar is essentially a mouth  with a huge vacuum-cleaner bag behind it which it constantly stuffs with food in order to grow as fast as possible (before it becomes one of the vast majority that get eaten). If you look at the first picture above, you will see that the dark area low down where the head is (on the right) has three slender reddish pairs of legs which will be its regular legs when it converts into a moth. Behind them are four pairs of round fat elephant legs, to support its long body that trails behind the "real legs." These are prolegs, that work fine as legs, but will disappear when the caterpillar develops into a moth. Most caterpillars have these, followed by a gap, and then at the tail end, one more pair of prolegs. What has happened here is that the furcula caterpillar has converted these into two long tentacles that it normally carries behind it (see second picture), but that when approached by a predator, it can pump fluid into to extend their length almost double.

What it does then, which you must see to believe (which you will see in the next series of pictures), is, it faces the approaching predator (in this case, my finger), throws those tails up over its head, extends them as long as it can, then slaps them down on the ground in front of its head (actually making a sound you can hear from a few feet away). It has very much the appearance of a scorpion striking its venomous tail down, and a small predator might very well move away, thinking it got off with a close call.

Now that little trick, pretending to be dangerous when it is actually harmless, and constantly eating, may get the defenseless caterpillar through this perilous period of its life as fast as possible before something catches and eats it. But there is still a serious hurdle to get over. It must spend many months in a cocoon changing from larva to adult, a time when it will be even more defenseless, even more slow moving, in fact not moving at all. Now every caterpillar faces this, and there are a number of dodges they use to get through it, maybe buried underground or under the leaf litter or camouflaged as chip of wood or a dried winter leaf. The furcula does this in its own way.

As you might have noticed, the White Furcula caterpillar comes in two color phases, green like this one we photographed in the wild doing its scorpion trick, and the yellow phase we photographed at the beginning of this blog, a different individual, which we brought home with us because it looked full grown, and we thought it was close to making its cocoon, and we wanted to watch the process.

Sure enough, after about a week it flattened itself against a narrow stick which was about its own diameter and spun a thin cage around itself, thin enough that we could still see it inside busily continuing with its spinning.

After several hours it had woven enough silk around itself that the cage was now opaque, and had somehow taken on the color of the stick.

And here is how (if we had left it outside) it would have spent the winter, hiding in plain sight disguised as a little thickening around a stick. We kept ours in a jar (just in case its trick didn't work) out in the unheated garage, knowing that it needed to experience some freezing temperature in order to complete the metamorphosis pattern and emerge at the right time. It had made its cocoon August 19, 2016.

Once it warmed up in spring, we moved the jar into the house and kept it on the dining room table, so we could keep a careful eye on it. On April 21, 2017 while we ate breakfast, we checked the jar and saw a hole in the side of the cocoon.

We took the moth out on the porch that night, took some pictures of it in the twilight, then let it go. Perhaps its final ploy was to become a beautiful moth so that we would feel well rewarded for looking out for it for eight months, giving it a slightly better chance of finding a mate, getting some eggs laid, and perhaps projecting itself into the next generation.