The hickory horned devil, show here, can reach more than 5 inches long and the size of a hot dog, making it Georgia’s biggest caterpillar. In the fall it burrows into the ground to pupate into a royal walnut moth. CONTRIBUTED BY BOB WARRICK/CREATIVE COMMONS

Caterpillars: the good, bad and ugly

A neighbor and her young son stopped by my home in Decatur last weekend to show me a frightful-looking creature that they were carrying in a large Styrofoam cup.

They had found it on the ground beneath a shade tree in their yard and had coaxed it into the cup. It was one of the scariest things they’d seen in a while, they said, and wanted to know what it was and if it posed danger to them or their pets.

Peering into the cup, I immediately recognized a hickory horned devil, which, at more then 5 inches long when fully grown, is Georgia’s biggest caterpillar. It is indeed fierce looking with its striking green color, black and white markings down the sides, spines on its back and red “horns” on its head.

All summer long it gobbles up the foliage of hickories, sweet gums, persimmons and other deciduous trees. By late summer, it is about the size of a hot dog and looks like a ferocious dragon.

But it is harmless. To show that, I gently pulled the humongous caterpillar out of the cup and held it in my hands. That drew a gasp from my neighbors, who then also wanted to hold it.

I told them that in late summer and early fall, hickory horned devils crawl from trees to burrow into the ground. They differ from most other caterpillars that spin cocoons or chrysalises. Instead, they burrow into the ground to pupate over the winter and emerge the next summer as a royal walnut moth. They are common in Georgia and cause little damage to trees, and so are not considered pests.

In general, September is peak time for most caterpillar species. Most of them are harmless, but a few species will sting the dickens out of you; in some people, they may cause severe allergic reactions. Stinging caterpillars in Georgia include the saddleback, tussock moth, puss moth, hag moth, Io moth, Isa moth and spiny oak slug.

The inch-long saddleback’s sting is particularly notorious. Its “saddle” is an oval purplish-brown spot in the middle of a green patch on the back.

IN THE SKY: From David Dundee, Tellus Science Museum astronomer: The moon, which was full on Friday, will still appear full tonight — the Harvest Moon. The only two planets visible now are Jupiter in the southwest around dusk, and Saturn in the south just after dark.

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