The browntail moth caterpillar is an invasive insect species that is found only in Maine and Cape Cod. When this insect is in its larval/caterpillar form, it damages trees, particularly fruit and oak trees. But this caterpillar is also considered a threat to public health, as this species possesses numerous poisonous hairs that protrude from its body like the quills on a porcupine. Although this caterpillar is categorized as an invasive threat to forest trees, the insects are also frequently found damaging trees located on residential properties in Maine.

Browntail caterpillars are particularly numerous in coastal areas of Maine, and large-scale invasions of these caterpillars are not unheard of in the state. During these invasions, the caterpillars become numerous near people’s homes where their poisonous hairs often come into contact with people’s skin, causing rashes and even respiratory symptoms. In fact, medically significant encounters between the caterpillars and humans become so frequent during invasions that pharmacies in Maine have had difficulty maintaining a full stock of prescription only medications that are specifically designed to address the rashes caused by these caterpillars.

During the early summer of 2016, browntail moth caterpillars invaded the midcoast of Maine, causing hundreds of people to suffer itchy rashes and respiratory problems after the caterpillar’s poisonous fibers were inhaled into the lungs. Within just two weeks into the invasion, the Kennebec Pharmacy in Brunswick sold 500 prescriptions of topical browntail moth medication. According to one pharmacist, around 40 to 50 people had been purchasing the medication per day. However, during the entire year of 2015, the pharmacy sold fewer than 500 prescriptions, demonstrating that the risk of falling victim to these caterpillars varies tremendously from year to year in Maine. During 2017, a bulletin put out by the Maine Organic Farmers and Growers Association warned homeowners in the state about the increased presence of browntail moth caterpillars on residential oak and fruit trees. Homeowners can check for browntail moth caterpillars within their trees by looking for the insects webs on the tips of tree branches.

Have you ever found what looked to be brown moth caterpillar webs on the trees in your lawn?