Caterpillars are the larval stage of moths and butterflies. While most are harmless, some possess specialized defense mechanisms that can cause irritation upon contact.
How Caterpillars Defend Themselves
Caterpillars do not possess stingers like bees or wasps, so they do not sting in the traditional sense. Instead, their primary defense mechanism involves specialized hairs, spines, or bristles, often referred to as urticating hairs. These structures are designed to deter predators and can cause irritation upon contact with human skin.
When these tiny hairs or spines are touched, they can break off and embed themselves in the skin. Many of these urticating hairs are hollow and connected to glands that produce toxins or irritants. Upon penetration, these chemical substances are released, leading to symptoms like pain, itching, redness, swelling, and sometimes welts or blisters. The severity of the reaction depends on the caterpillar species, the degree of contact, and an individual’s sensitivity. Some caterpillars can even shed these hairs, which can then become airborne and cause reactions if they land on skin, eyes, or are inhaled.
Recognizing Potentially Irritating Caterpillars
Identifying caterpillars that can cause skin irritation involves observing their physical characteristics. Caterpillars with a fuzzy appearance, prominent spines, or distinct color patterns are more likely to possess irritating hairs and should be avoided. Many irritating species are found in gardens, forests, or on various trees and shrubs.
Examples of well-known irritating caterpillars include the puss caterpillar (also known as the southern flannel moth caterpillar), which is covered in a dense, woolly coat of soft brown hair that conceals hidden venomous spines. Saddleback caterpillars are another species, recognizable by their brown ends and a green middle with a brown oval resembling a saddle, possessing stinging hairs along their sides. Io moth caterpillars are pale green with a white and red stripe and have yellow or green fleshy protrusions tipped in black that contain stinging spines. Other species like tussock moth caterpillars and buck moth caterpillars also have urticating hairs that can cause reactions.
Responding to Caterpillar Contact
If contact with an irritating caterpillar occurs, immediately remove any remaining hairs or spines from the skin. Apply adhesive tape to the affected area and carefully pull it off. Repeat this process until no more hairs are visible.
After removing the hairs, thoroughly wash the contact area with soap and water. Applying a cold compress or ice pack to the affected area can help reduce swelling and pain. Over-the-counter treatments like baking soda paste, corticosteroid creams, or oral antihistamines can also provide relief for itching and inflammation. Seek medical attention if symptoms are severe, include difficulty breathing, widespread rash, or any signs of a severe allergic reaction, such as anaphylaxis, though this is rare. Wearing gloves and long sleeves when gardening or in areas known to have irritating caterpillars can help prevent accidental contact.