The brown tail moth (BTM) caterpillar, an invasive insect, represents a significant concern for the health of hardwood trees and public health. These caterpillars cause severe skin irritation and respiratory issues in humans, making their control and eradication urgent. The following methods provide practical strategies for safely controlling and eliminating brown tail moth caterpillars from your property.
Understanding the Health Hazard
The brown tail moth caterpillar possesses microscopic, toxic hairs, known as setae, which are the source of the severe health hazard. These tiny, barbed hairs contain a toxin that causes a rash similar to severe poison ivy upon contact with human skin. The rash is typically red, bumpy, and intensely itchy. A major concern is that the hairs can easily break off from the caterpillar’s body and become airborne, meaning direct physical contact is not required to be affected. These hairs can land on outdoor surfaces and can be inhaled, potentially causing respiratory distress that may require medical attention. When working in or near an infested area, wear protective gear, including long sleeves, gloves, goggles, and a respirator or mask, to prevent exposure.
Targeting the Life Cycle
Successful control of brown tail moth populations relies heavily on precise timing, targeting the insect during its most vulnerable life stages. The most effective control measures focus on the dormant and early feeding stages. Adult moths lay eggs in late July and August; the caterpillars hatch soon after, feeding briefly before constructing their overwintering nests. The first control window is during the winter months (October to mid-April), when the caterpillars are dormant inside their silken webs, or hibernacula. The second opportunity is in the early spring (mid-April to the end of May), when the tiny caterpillars emerge to begin feeding on new foliage. Spraying treatments later in the summer, when the caterpillars are fully mature, is less effective and increases the risk of hair dispersal.
Physical Removal of Overwintering Webs
Manual removal of the overwintering webs is the least toxic and most direct control method, best performed during the dormant season between October and mid-April. These webs are generally palm-sized, silken nests found at the tips of branches, containing hundreds of hibernating caterpillars. Removing webs during the winter, after the leaves have fallen, makes them easier to spot and remove. To safely remove the webs, use a pole pruner or hand snips to clip the tips of the branches holding the nest. Always wear protective clothing, including tight-fitting coveralls, gloves, and eye protection, as the webs contain toxic hairs, even when dormant. After removal, the clipped webs must be immediately collected in a bucket to prevent any live caterpillars from emerging or the hairs from dispersing. The webs must be destroyed by either soaking them in soapy water for several days or by carefully burning them in a contained, legal fire.
Applying Chemical and Biological Controls
For active infestations or webs in tall, inaccessible trees, chemical and biological controls are necessary and should be applied by a licensed professional. The timing of these applications is strictly limited to the early spring, generally before the end of May, to target the young, actively feeding caterpillars. Treatments applied after this window are significantly less effective and do not mitigate the public health risk.
Biological Control
The most common biological option is a product containing Bacillus thuringiensis (Bt), a naturally occurring soil bacterium that acts as a targeted insecticide. Bt must be ingested by the caterpillar to be effective, making it an ideal choice for the early spring when the larvae are actively feeding on new leaves.
Chemical Control
For chemical control, synthetic pyrethroids, such as permethrin or deltamethrin, are contact insecticides that can be used on foliage. Their use requires careful consideration of environmental impact and local regulations. Professional applicators can also use systemic treatments, such as tree injections, which deliver the control agent into the tree’s vascular system, thereby killing feeding caterpillars over a longer period.