What Parents Should Know About Caterpillars

They may be the teddy bears of the bug world, but some can cause painful rashes.

White-marked tussock moth caterpillar - Photo by Steven Brewer

Of all the creepy-crawlies kids come in contact with outdoors, caterpillars seem pretty harmless. After all these fuzzy little creatures are kind of cute—and eventually, they turn into butterflies (or moths). However, while it’s true that most of the time an encounter with a caterpillar isn't as potentially dangerous as, say, a bee sting or a tick bite, caterpillars aren't always as innocent as they look.

So while your child may find it fun to pick up a caterpillar and let it wander all over his hands and body, he could be inviting an itchy, perhaps even painful, rash.

Look, but Don't Touch

The caterpillar characteristic that's usually most tempting—the fuzzy tufts that make them seem like the cuddly stuffed toys of the insect world—is the one that can cause trouble. Experts don't totally understand why, but it's thought that the tiny hairs, called setae, contain a chemical called a histamine that sets off an allergic reaction. The friction of the hairs against the skin also may irritate skin. And some species of caterpillar can sting.

A rash caused by touching a caterpillar can look like welts, small, fluid-filled sacs called vesicles, raised red bumps, or areas of red, scaly skin. Sometimes a child may feel mild to moderate stinging or pain. These symptoms can appear within minutes of touching a caterpillar and last for one or more days.

If a little one happens to put a caterpillar in his mouth or touch his eyes after handling one, there could be a more serious reaction. He could have trouble breathing or swallowing, develop hay fever-like symptoms, or come down with conjunctivitis (an eye infection also known as pink eye).

What makes reactions to caterpillars most confounding is that they can easily be mistaken for something else and therefore not treated properly.

In 2011, for instance, 23 children at two daycare centers and one elementary school in Florida got rashes from exposure to white-marked tussock moth caterpillars. According to a report by the Centers for Disease Control and Prevention (CDC), most of the kids were first misdiagnosed with a variety of issues, including viral rash, chicken pox, molluscum contagiosum, and even MRSA folliculitis. (MRSA stands for Methicillin-resistant Staphylococcus aureus, a bacterium that's resistant to certain antibiotics.) In other cases, rashes caused by caterpillars have been mistaken for scabies, flea bites, mosquito bites, ​scarlet fever, fifth disease, and contact dermatitis

It's important to know that sometimes a child can get a rash without actually putting his fingers on a caterpillar, especially in areas where there are a lot of the critters at once. The little tufts can become airborne and land on bare skin. They also can leave setae behind on items kids commonly come in direct contact with. One of the recommendations by the CDC in response to the Florida outbreak was to advise schools and daycare centers where caterpillars are common to power wash playground equipment.

Treating a Caterpillar Rash

Given how easy it is to mistake a caterpillar rash for something else that potentially can be more dangerous, if your kid develops an itchy, mysterious rash you may want to have your pediatrician take a look at it.

And of course, let the doctor know that your child has been around caterpillars.

Let's say you see your child actually touch a caterpillar and have an immediate reaction. The first thing you should do is remove as many of the tiny hairs that will have rubbed off on his skin as possible. You can do this with adhesive tape: Rub a strip of tape onto the area where the hairs are and pull them off, like you would to remove lint from a piece of clothing. Repeat with fresh tape until you think you've gotten all the hairs you can. Then wash the area with soap and water and dab on a topical, low-potency steroid cream.

If the rash really stings, an ice pack can relieve the pain.

Sources:

Centers for Disease Control and Prevention. "Caterpillar-Associated Rashes in Children — Hillsborough County, Florida, 2011." Morbidity and Mortality Weekly Report. March 30, 2012 / 61(12);209-211.

Hossler, EW. "Caterpillars and Moths: Part II. Dermatologic Manifestations of Encounters With Lepidoptera." J Am Acad Dermatol. 2010 Jan;62(1):13-28.

 

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