The Giant Silkworms

(Written in the fall of the 1996) This year has been a good one for caterpillars. The orange striped oakworm was the most abundant I have ever seen. There are several other caterpillars feeding on deciduous plants right now. Some of the most spectacular belong to a group of insects known as the Giant Silkworms.

These are noticed because they are huge. Generally they don't cause major damage. They are evidently tasty and if there are too many in an area birds will clean them up. I get the most calls about the Hickory Horned Devil. This caterpillar will get up to 5 inches long and has five bright colored horns.

About half of the callers want to know how to raise the caterpillar to see the moth. The Hickory Horned Devil will feed on hickory, walnut, butternut, ash, sumac, sweetgum or persimmon. Unless you notice what the particular individual was feeding on, you may not have good results. Individuals will have a preference toward one species or another. In different areas there seems to be populations that are genetically set up to use a certain plant species and they will not develop as well on other plants. If you can provide the correct food, I would guess you could raise them.

The giant silkworms need more than a jar or 2 liter plastic bottle. The amount of moisture they give off plus the amount of droppings would create a mess in a small container. If the caterpillars get down in the moisture it could cause sickness and death. An aquarium would work. Do not place it in direct sunlight.

Once they spin a cocoon, I would try to let them get some cold treatment. I don't have any scientific evidence this is necessary but it is what they would get in nature. I expect cold treatment of 40 degrees for 12 weeks would be enough. The refrigerator would be fine if you have a tolerate wife. I collected a couple of cocoons in January one year and brought them inside my office. Later in the year they hatched so if cold treatment was necessary they had enough by January.

The one that hatched in my office was a Polyphemus Moth. Polyphemas was a one eyed giant in Greek mythology. These moths have a large spot on the hind wings. I collected those two off a plum tree. Normally, the caterpillars will eat alder, basswood, birch, elm, hickory, maple, poplar or sycamore.

The other cocoon had already been parasitized by a small wasp. It had a small exit hole in the side where the wasp had come out.

While Polyphemus moths with a 5-inch wingspan are remarkable, I remember one of its cousins even better. This is the Luna moth. This striking pale green moth has long tails. Last week a person brought an Imperial moth to my office. This large green caterpillar feeds on a variety of broadleaf and conifer plants. The person discovered it on a silver maple. Adults are becoming rarer because they are attracted to artificial light. This makes it easier for birds to prey on them.

Despite the imposing appearance of these caterpillars neither the Hickory horned Devils nor the Imperial moths are harmful to man.

To my knowledge the only one in this family that hurts is the Io moth. It has spines that branch along with reddish and white stripes on the side.

In conclusion, the giant silkworms are another group of caterpillars eating the foliage in late summer. Like other caterpillars this time of the year they should be admired and not expired.


Article was written by David Goforth Agriculture Extension agent North Carolina Cooperative Extension Cabarrus County Center.  Visit my homepage or or my blog

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