SADDLE BACK CATERPILLAR

It was a beautiful day for working outside on bonsai trees. The summer breeze was just right, so with pruners in hand I began my work. I was putting a hornbeam I had just pruned back on the bench when I felt a sting on my arm. On the leaf of a Japanese Maple I had just brushed past was a creature that looked like a “B” movie alien. It was the saddle back caterpillar.

The saddle back caterpillar, Acharia stimulea (formerly Sibene stimulea) is the larva of a species of moth native to eastern North America. The species belongs to the family of slug caterpillars, Limacodidae. The caterpillar is primarily green with brown at either end, and a pronounced white-ringed brown dot in the center which resembles a saddle. It was a pair of fleshy horns at either end.

As you see circled above, these horns and most of the rest of the body bear urticating hairs that secrete irritating venom. 

 





Contact with the hairs causes a painful, swollen rash, and sometimes nausea in humans.                     

Rash from caterpillar hairs.

The hairs should be removed from the skin immediately to prevent the venom spreading. The cocoon may also have irritating hairs, and hairs from the larva can fall onto surrounding objects.

Cocoon of Saddleback Caterpillar

The larva feeds on a large variety of plants. 

The adult is a dark brown, stout-bodied moth as seen below.

The white discs seen on the caterpillar pictured below are cocoons from braconid wasps. They laid eggs on the unfortunate caterpillar in late August, consumed part of his insides and have now emerged to pupate.

In all, the stinging sensation lasted about four hours, and felt similar to a jellyfish sting. 

For general treatment of a sting, follow these steps:

1. Remove caterpillar (or hairs) from your skin.

2. Wash affected area with soap and water.

3. Apply an ice pack or a wet cloth to the stinging area.

4. You can use a topical anesthetic for pain.

5. Monitor the sting for swelling or changes in coloration. If symptoms don’t improve, seek medical attention.

Saddleback caterpillars can be found on most deciduous trees (e.g., chestnut, cherry, basswood, oak, plum and maples) and sometimes on corn.