The Brown Tail Moth (Euproctis chrysorrhoea) is an invasive species that poses a significant public health nuisance, particularly in its caterpillar stage. Unlike insects that sting or bite, the danger is indirect and purely defensive. The health hazard comes from microscopic structures the caterpillar sheds into the environment, leading to widespread human exposure. This unique mechanism means people can experience adverse reactions even without directly encountering the insect.
The Biological Source of Irritation
The source of irritation comes from thousands of tiny, barbed hairs, known as setae, that cover the body of the brown tail moth caterpillar. These hairs contain a toxin that triggers a reaction in the human body. The resulting irritation is both physical, as the barbed hairs embed in the skin, and chemical, due to the toxin.
The setae are easily shed when the caterpillars are disturbed and can become airborne, traveling on the wind or being stirred up by outdoor activities. The greatest risk of exposure occurs between April and July when the caterpillars are most active. Once shed, the hairs remain toxic in the environment for an extended period, sometimes up to three years. This persistence means hairs can be found on grass, leaves, outdoor equipment, and even dried laundry.
Recognizing Symptoms of Exposure
Exposure to the barbed hairs results in lepidopterism, which manifests primarily as a skin rash. The characteristic reaction is often described as feeling similar to a severe case of poison ivy, presenting with intense itching (pruritus), redness, and inflammation. This ‘brown tail moth rash’ appears as red maculo-papules that may sometimes be tinged with orange at the center.
The rash can appear on any area where the airborne hairs land, including exposed skin and areas covered by loose clothing. While most people experience a localized rash that resolves within a few hours to several days, severe reactions can last for several weeks in sensitive individuals. Inhaling the microscopic hairs can also lead to upper respiratory issues. Symptoms may include rhinitis, conjunctivitis, difficulty breathing, or asthma-like symptoms.
Protection, Prevention, and Treatment
Mitigating the risk requires a two-pronged approach: environmental management and personal protection. The most effective preventative measure is the safe removal of the caterpillars’ silken winter webs. These nests are best clipped from tree branches between October and mid-April, before the caterpillars emerge to feed. The clipped nests should be destroyed by freezing or soaking them in soapy water before disposal.
Personal protective equipment is necessary when working in infested areas, especially during the peak caterpillar season from spring through mid-summer. When performing activities that may stir up hairs, such as mowing, raking, or leaf blowing, cover all exposed skin. This includes wearing long sleeves, long pants, a hat, and protective eyewear. Wearing a dust mask helps prevent the inhalation of airborne hairs. Performing yard work on damp days also minimizes risk, as moisture keeps the hairs from becoming easily airborne.
For immediate first aid following exposure, the goal is to remove embedded hairs and soothe the irritation. Applying adhesive tape to the affected skin helps gently lift out any surface hairs. Immediately changing clothes and taking a cool shower is also recommended to wash off remaining hairs. Over-the-counter treatments are typically sufficient for managing rash symptoms, including applying calamine lotion, hydrocortisone cream, or taking an oral antihistamine. Professional medical attention should be sought if the rash is widespread, persistent, or if respiratory symptoms like difficulty breathing or throat swelling occur.