Jennifer Schultz Nelson
Extension Educator, Horticulture
If asked to name a stinging insect, most people would give answers like bee, wasp, or hornet. A Master Gardener came to me this week with a story of his neighbor that had encountered a Saddleback caterpillar, which has the ability to "sting".
I had never heard of a Saddleback caterpillar. A quick search on the internet revealed that I certainly would have remembered it if I had seen it! The Saddleback caterpillar is a deep brown with a bright green middle that looks somewhat like a saddle with a big white-ringed purple-brown spot in the center. Large horn-like appendages extend from each end of the caterpillar, covered in spines. Smaller tufts of spines extend along each side of the caterpillar.
The Saddleback caterpillar, Sibene stimulea is the larval stage of a moth native to Eastern North America. The adult form is a rather hairy, plain brown moth that most people wouldn't pay much attention to. Both the larvae and the adult are about an inch long. Larvae generally lead solitary lives, feeding on a wide variety of deciduous trees and occasionally corn. They don't typically occur in numbers large enough to cause extensive damage to plants.
Saddleback caterpillars are part of a group of caterpillars called slug caterpillars. These caterpillars are short and stocky, moving over plants much like a slug, their head and legs hidden from view. Some species in this group, like the Saddleback caterpillar, have tufts of short, stinging bristles. These bristles serve as protection from predators. The bristles are even incorporated into their cocoons, to protect the pupa as it turns into a moth.
The stinging bristles of the Saddleback caterpillar are unique structures. They are called urticating hairs, essentially hollow structures with a barb at the end designed to break off and lodge in the skin of a predator, delivering an irritating poison directly into the skin. Plants such as the stinging nettle have urticating hairs, and animals such as tarantulas have them as well.
The bright coloration of the Saddleback caterpillar serves as a warning to most living things to stay away from the Saddleback caterpillar, but occasionally they cross our path. It may be tempting to sweep them away with your hand, but just a light brush against the bristles will lodge them in your skin.
The sting from the bristles has been compared to that of a bee sting. Severity of the sting is dependent on how many of the bristles come in contact with your skin, and how sensitive your skin is. Symptoms range from redness and swelling to burning, itching and severe pain. Extremely sensitive individuals may need medical treatment. Stinging in or around the eye is serious and can cause blindness.
If stung by a Saddleback caterpillar, immediately applying adhesive tape to the area to remove as many of the bristles as possible may help. Wash the area thoroughly and apply ice packs and a paste of baking soda and water to reduce pain and swelling. Over-the-counter antihistamines and topical corticosteroids may help reduce symptoms.
Removing Saddleback caterpillars from an area is best done with a stick, garden tool, or other object. Even gloved hands are susceptible to the stings, since the bristles can lodge themselves in thin gloves or clothing. Use caution when working in the woods or cornfields—two places Saddleback caterpillars are commonly found. Wearing heavy gloves, long sleeves and pants will provide some protection.
It is also a good idea to teach children to not handle colorful fuzzy or hairy caterpillars. While not every hairy caterpillar is harmful, better to err on the side of caution. Personally, I'm amazed I have not encountered this caterpillar before—I was the child that collected every caterpillar she could get her hands on! But just the description of the burning pain that typically accompanies the Saddleback caterpillar sting is enough to convince the curious child in me to keep my distance.