Woolly bear caterpillars, the larval stage of the Isabella tiger moth ( Pyrrharctia isabella ), are a familiar sight, particularly in autumn. These fuzzy creatures often spark curiosity. A common question concerns their potential danger or toxicity upon contact. This article clarifies their characteristics and addresses concerns about human interaction.
Identifying Woolly Bear Caterpillars
Woolly bear caterpillars have a segmented body covered with dense bristles, known as setae. These bristles typically form bands of black at the ends and a rusty-brown band in the middle, though variations in color and patterns occur, with some appearing entirely black or more yellowish. They move with a distinctive wriggling motion.
These caterpillars are commonly found in gardens, fields, and woodlands across the United States and southern Canada. Their broad diet includes low-growing plants like dandelions, clovers, plantain, and sometimes garden vegetables. Woolly bears overwinter as caterpillars, surviving freezing temperatures by producing a natural cryoprotectant. In spring, they thaw, feed briefly, then pupate, eventually emerging as Isabella tiger moths.
The Truth About Their Bristles
Woolly bear caterpillars are not poisonous or venomous. Their bristles, or setae, do not contain venom-injecting mechanisms. Unlike some other hairy caterpillar species with stinging hairs and toxins, woolly bear bristles are primarily a physical defense against predators like birds. When disturbed, they may curl into a tight ball, protecting their vulnerable undersides and presenting their stiff bristles.
Contact with these bristles can cause mild skin irritation in some sensitive individuals. This irritation is a mechanical reaction, occurring because the barbed bristles can break off and lodge in the skin. Symptoms might include localized redness, itching, or a slight burning sensation. Such reactions are generally minor and temporary, differing significantly from a toxic or allergic response.
After Contact: What to Do
If skin irritation occurs after contact with a woolly bear caterpillar, prompt action can help alleviate discomfort. Gently wash the affected area with soap and water to clean the skin and remove any loose bristles. Avoid rubbing, as this can push bristles deeper into the skin.
To remove any remaining bristles, gently press adhesive tape (such as duct or masking tape) onto the affected skin and pull it off. This method helps lift embedded hairs. For minor itching and discomfort, applying a cool compress or ice pack for 10-15 minutes can provide relief. Over-the-counter remedies like calamine lotion, a paste made from baking soda and water, or hydrocortisone cream can also help soothe irritated skin. While severe reactions are rare, seek medical advice if symptoms worsen, persist, or if signs of infection appear.