When discussing poisonous caterpillars, the term refers to species that possess defensive structures capable of injecting irritating or venomous substances upon contact. These structures are specialized hairs or spines known as urticating hairs. Instead of being toxic if ingested, the danger to humans comes from physical interaction with these hairs, which can cause skin irritation, pain, or allergic reactions.
General Warning Signs
Certain visual cues can indicate a caterpillar might be equipped with defensive mechanisms. Bright, contrasting color patterns, known as aposematism, often serve as a warning to predators that the organism is unpalatable or dangerous. For instance, caterpillars with alternating bands of vibrant colors like orange and black frequently signal toxicity.
Many dangerous caterpillars also feature dense clusters of spiny or hairy protrusions covering their bodies. These can give them a fuzzy or bristly appearance. These hairs or spines are often hollow and connected to venom glands, designed to break off and deliver irritants when touched. Some caterpillars might also exhibit unusual shapes or a particularly “furry” texture, which, while appearing soft, can conceal stinging hairs.
Common Poisonous Caterpillars and Their Appearance
Several caterpillar species are widely recognized for their stinging capabilities, each possessing distinct appearances.
The Saddleback Caterpillar (Acharia stimulea) is identified by its slug-like body, primarily green with brown areas at both ends. A prominent brown dot encircled by a white ring in the center of its back resembles a saddle, giving it its name. This species, native to eastern North America, also has fleshy horns at each end of its body, all bearing urticating hairs that secrete an irritating venom.
The Puss Caterpillar (Megalopyge opercularis), also known as the Southern Flannel Moth caterpillar, is notably furry in appearance, covered by thick, tan to grayish-white hairs. These caterpillars, found across the Southeastern United States and Mexico, have venom-filled spines hidden beneath their soft-looking outer hairs. They can grow up to an inch long and have a tear-drop shape, with their head and legs concealed by the dense hair.
Another stinging species is the Io Moth Caterpillar (Automeris io). Young caterpillars are initially orange and group-living, but as they mature, they transform to a bright green or yellowish-green color with a distinctive red and white stripe running along their sides. Their bodies are thickly covered with bristly, needle-sharp spines, each a hollow tube filled with toxin. Io Moth Caterpillars are found throughout North America, from Canada to Mexico.
The Buck Moth Caterpillar (Hemileuca maia) is a large, dark caterpillar, reaching about 2 to 2.4 inches in length. Its body is black, often with small white spots, and it possesses a reddish head and legs. The body is covered with tufts of short spines at the base of longer, branched spines, which are hollow and connected to venom glands. This species is distributed from Maine to Florida and west to Texas, primarily feeding on oak trees.
What to Do After Contact
Should skin contact occur with a poisonous caterpillar, immediate action can help minimize the reaction. The first step involves carefully removing any embedded hairs or spines from the affected area. This can be achieved by gently applying adhesive tape to the skin and then peeling it away, which helps lift the irritating structures.
Following the removal of hairs, thoroughly wash the affected skin with soap and water to cleanse the area and reduce any remaining irritants. Applying ice packs to the site can help alleviate pain and swelling. Over-the-counter topical creams containing corticosteroids or antihistamines may also provide relief from itching and inflammation. Monitor the affected area for severe symptoms such as intense pain, extensive swelling, widespread rash, or signs of an allergic reaction like difficulty breathing or dizziness. If these symptoms develop, professional medical attention should be sought promptly.