What Parents Should Know About Caterpillars

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Of all the bugs and insects kids come into contact with, caterpillars seem pretty harmless. After all, these fuzzy little creatures are kind of cute, and, eventually, they turn into butterflies or moths. While it’s true that 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 children may find it fun to pick up and play with a caterpillar, they could be inviting an itchy and even painful rash.

Caterpillar Rash Symptoms
Verywell / Brianna Gilmartin

Causes and Symptoms

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.

It is thought that exposure to the creature's tiny hairs, called setae, triggers an overactive immune response in some people. Reacting to what it perceives to be a threat, the immune system will flood the body with a pro-inflammatory compound called histamine. This can incite an array of allergic symptoms involving the skin, eyes, and respiratory tract.

Touching a caterpillar can cause redness, swelling, itching, rash, welts, and small, fluid-filled sacs called vesicles. There may also be a burning or stinging sensation.

Other species of caterpillar, like the southern flannel moth (Megalopyge opercularis) indigenous to parts of Texas, are known to inflict stings and trigger a localized skin reaction.

See the photo below for an example of what symptoms of a rash caused by a caterpillar may look like on a human arm.

This photo contains content that some people may find graphic or disturbing.

Red blisters caused by hairy caterpillar
Caterpillar rash. iStock / Getty Images Plus

These symptoms can appear within minutes and last for one or more days. If a child touches their eyes or nose after handling a caterpillar or places one in their mouth, there could be a more serious reaction. There may be sneezing, coughing, runny nose, red eyes, shortness of breath, mouth pain, itching, and difficulty swallowing.

Misdiagnoses

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

In 2011, 23 children in Florida developed rashes from exposure to white-marked tussock moth (Orgyia leucostigma) caterpillars. According to the report issued by the Centers for Disease Control and Prevention, most of the kids were initially misdiagnosed with a variety of conditions, including chickenpox, molluscum contagiosum (a sexually transmitted infection), and even potentially life-threatening MRSA infections.

In other cases, rashes caused by caterpillars have been mistaken for flea bites, mosquito bites, scabies, scarlet fever, fifth disease (parvovirus B19), 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.

Treatment

If your child develops a rash after an encounter with a caterpillar, it usually won't be serious and can be treated at home. If the reaction is immediate and mild, you will first need to remove as many of the tiny hairs that have rubbed off onto the skin.

To do this, simply rub a strip of tape across the affected skin as you would with a lint roller. Repeat with fresh pieces of tape until you've gotten out all of the hair that you can.

Afterward, wash the skin with soap and water and dab on a low-potency steroid cream. If the rash really stings, the 10- to 15-minute ice application can usually help relieve the pain.

On the other hand, if there is extreme swelling with or without respiratory symptoms, it is best to play it safe and either call your pediatrician or go to your nearest urgent care center.

Though extremely rare, there have been cases of anaphylaxis in children who have touched certain caterpillars. In 2014, a five-year-boy in northeast Ohio nearly died after an encounter with a spotted tussock moth (Lophocampa maculata) caterpillar.

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