My older son has three stick insects (order Phasmatodea) living in a vivarium. He calls them “stick bugs.” They were given to him by his science teacher last fall. We figured they were going to part of some school science project, but so far there’s been no curricular connection. Meanwhile, the phasmids have grown. When we got them in September, they were each about an inch long. Now the longest of them is nearly four inches in length, though at first glance it often looks longer because of its penchant for sticking its two forelegs straight out in front of it. (In the picture below the insect in the foreground is standing next to an actual stick.)

My son’s teacher said that he was giving us three insects in the hope that there would be two different sexes among the trio, enabling them to have babies. We haven’t figured out precisely what species of phasmid these are. I’d assumed that they were the most common type, the Indian or Laboratory stick insect (Carausius morosus). But the Indian stick insect reproduces parthenogenically, and ours haven’t reproduced at all. (One of my son’s friends was luckier: his insects laid eggs, which hatched. Of course, the adults then ate the young …)

The phasmids eat lettuce, and they molt periodically. The picture below shows a complete molted exoskeleton. Apparently the insects find their old shells tasty, so often these ghostly skeletons will disappear from the vivarium after a few days. The newly molted insect is a plant-like green, but it soon returns to its bark-like brown coloring.

The phasmids seem to be more active at night. During the day they prowl around the vivarium a little bit, but mostly they’re still and rather stick-like. I keep asking my son if he’ll let me take them out of the cage for a little exercise in the hallway, but so far he’s refused all requests. My wife isn’t so crazy about the idea of walking the stick bugs either.

But here’s what’s really cool about stick bugs: they can regenerate limbs. Two of the insects were damaged when we received them: the biggest was missing its right foreleg, and another was missing its left hindleg. Then, one morning I noticed that the smaller one had all of its legs. It had grown a new hindleg, which was in fact bigger than its surviving hindleg. A few weeks later, the big one regenerated its foreleg. The new legs seemed to have regrown under the exoskeleton and then uncurled after molting.

How marvelous to be able to regrow a lost limb! No need for the bluetooth bionics that are being tested these days on veterans of the Iraq war who have had their legs amputated (click here for a CNN report.) Of course, in my current state, I’d be happy with the ability to regenerate damaged knee cartilage spontaneously.

On the other hand, stick bugs don’t live very long: life expectancy for most species is less than a year. I guess you can’t have everything.