Many fuzzy caterpillars appear soft and inviting, but their appearance can be deceiving. While not all are dangerous, some possess defensive mechanisms that can cause adverse reactions if touched. Understanding the distinctions between harmless and harmful species is important for safe interaction.
How Caterpillars Protect Themselves
Caterpillars employ various defense strategies, often involving specialized hairs and toxins. Many fuzzy caterpillars have “urticating hairs” or bristles that act as a physical irritant. These hairs can be barbed or contain a weakened ring at their base, allowing them to easily break off and embed in the skin, causing itching or a burning sensation.
Some caterpillars connect these hairs to venom glands, delivering toxins upon contact. These venomous hairs act like miniature hypodermic needles, injecting irritating fluid. While skin contact is the primary concern for humans, some caterpillars also contain toxins that can cause harm if ingested.
Fuzzy Caterpillars to Approach with Caution
Several fuzzy caterpillar species cause painful reactions upon contact due to their venomous hairs.
Puss Caterpillar
The puss caterpillar (Megalopyge opercularis), often called an asp, is teardrop-shaped and covered in long, silky hairs resembling a tuft of cotton or fur. It can range in color from yellow to gray or reddish-brown. Beneath its soft appearance are hollow spines filled with venom, causing immediate, intense burning pain, a rash, swelling, and sometimes more severe symptoms like nausea, headache, fever, or difficulty breathing.
Saddleback Caterpillar
The saddleback caterpillar (Acharia stimulea) is another species to avoid. It is bright green with a distinctive purplish-brown “saddle” marking and has fleshy horns and smaller knobs along its sides. These bear urticating hairs that secrete an irritating venom. Contact with these spines can result in severe pain, redness, itching, and a rash, with rare cases leading to difficulty breathing or anaphylactic shock.
Io Moth Caterpillar
The Io moth caterpillar (Automeris io) also poses a risk. It is light green with red and white stripes and covered in stinging spines. Stings can cause immediate stinging and itching, followed by a localized welt, redness, and in some instances, more systemic symptoms like headache, nausea, or muscle spasms.
Fuzzy Caterpillars That Are Safe to Observe
Not all fuzzy caterpillars are harmful; many can be observed without concern.
Woolly Bear Caterpillar
The woolly bear caterpillar, larval form of the Isabella tiger moth (Pyrrharctia isabella), is widely recognized for its dense coat of black and rusty brown bristles. These caterpillars are generally harmless to touch, though their bristles can cause mild irritation for sensitive skin or if they break off. They are often seen slowly crawling across roads in the fall.
American Dagger Moth Caterpillar
The American dagger moth caterpillar (Acronicta americana) is another safe fuzzy species. It has long, pale yellow-white hairs covering its body, giving it a soft appearance, along with two pairs of long black hair pencils near its head and one at its rear. Despite its name, this caterpillar does not possess venomous hairs.
Giant Leopard Moth Caterpillar
Similarly, the giant leopard moth caterpillar, which resembles a woolly bear but lacks the orange band, is also safe to handle. This large, two-inch long caterpillar will roll up to reveal red bands on its skin when disturbed.
Steps to Take After Exposure
If you contact a potentially harmful fuzzy caterpillar, immediate action can help minimize discomfort. First, gently remove the caterpillar without using bare hands, perhaps with tweezers or a stick, to avoid further exposure. Next, apply adhesive tape, such as scotch tape or duct tape, to the affected skin and pull it off. This helps remove any embedded hairs or spines.
After removing the hairs, thoroughly wash the area with soap and water. To alleviate symptoms like itching, pain, and swelling, apply a cold compress or ice pack wrapped in a cloth for about 20 minutes. Over-the-counter remedies like hydrocortisone cream or a baking soda and water paste can also help reduce itching and inflammation. Seek medical attention if symptoms are severe, include difficulty breathing, significant swelling, signs of infection, or if the reaction affects the eyes.