Not Too Many Hornworms

If it weren't for the silky white blobs, the first feature you might notice is the series of "eye spots" (actually breathing holes), seven of which are topped with white-and-blue slash lines. These lines break up the shape of this sphinx moth caterpillar, which otherwise might be hard to miss since it grows to six inches long.

And then you notice that red, nasty stinger-looking thingy that curves up from its butt. The head is at the other end, by the three pairs of true legs.  Lots of people, and some potential predators, are reluctant to tangle with this caterpillar because of that "stinger." Actually it's all bluff. The horn is harmless.

This caterpillar eats the leaves of tomato, potato, and other plants of the nightshade family. At maturity, successful hornworms burrow into the soil to escape predators, pupate, and turn into sphinx moths. The moths are sometimes mistaken for hummingbirds; they dart from flower to flower at dusk. Long tongues enable them to pollinate such specialized blossoms as the prairie white-fringed orchid.

But the hornworm shown here will not graduate to experience the miracle of flight. Some weeks earlier it had been attacked by a parasitic wasp, which injected eggs under its skin. The little baby wasps ate much of the inside of the caterpillar before crawling back out and spinning their own cocoons, which they attached to their host.

It's a bug-eat-bug world. And that's a good thing. Otherwise we'd be overrun with bugs. There are more than one hundred thousand species of parasitic wasps known, and they're a major force for maintaining balance in nature. Birds, bacteria and diverse other organisms keep caterpillars and butterflies at an enjoyable level.

One day Pete Leki, whose vegetable garden is on the northwest side of Chicago, found a large hornworm in his tomato plants. He showed it to his family and they marveled over it — then recoiled in shock and wonder when its back erupted with wasp larvae, which spun cocoons and installed them on little stalks so they looked like white, silken lollipops.

Pete's family was just absorbing the predator idea when another species of wasp showed up and started harvesting the new cocoons. It sheared them off low, used their handy stems to accumulate a big mouthful, and flew away with them to provision its own young. A splendid lesson in complexity and balance.

The gypsy moth couple shown above is engaged in the process of reproduction. Our continent is still poor in the natural enemies of these invaders. As Arthur Pearson outlines in his article in this issue, this moth has many predators and diseases. Learning to encourage those natural enemies is the best way to lessen the damage from inevitable gypsy moth plagues.