SKAGIT COUNTY, Wash. — The Western Tent caterpillar population has recently exploded on Guemes Island, with some residents even saying they're shoveling the insects off driveways and walkways.
The caterpillar, which gets its name from a dense tent-like web that larvae live and feed inside, has one generation each year. The caterpillars emerge for four to six weeks between mid-May and June to search for a place to pupate, according to Washington State University's (WSU) website on tree fruits and orchard pest management.
Western Tent caterpillars spend the winter as eggs and emerge as larvae sometime between March and June. The caterpillars cocoon themselves between June and July, then emerge as a reddish brown moth between July and August, according to WSU.
During outbreaks, swarms of moths can be common, according to the United States Department of Agriculture (USDA). The moths lay eggs on live branches of a host tree.
The caterpillar is more of a nuisance than a damaging pest, according to the USDA. Tree hosts include alder, cottonwood, crabapple, fruit trees, oak, poplar, and willow, among other species that may be more popular with the caterpillar depending on the region.
Larvae are known to strip the leaves of their host trees if allowed to develop, according to WSU. Successive years with stripped leaves can be damaging to some tree species, potentially leading to reduced production in fruit trees, and even tree death in some extreme cases, according to the USDA.
While Western Tent caterpillars are not known to be severely damaging to trees, infestations are typically allowed to run their course, however, several chemical and biological insecticides are used for population control amid outbreaks, according to the USDA.