Massachusetts Introduced Pests Outreach Blog

Reports sometimes come in through our ALB reporting form from Massachusetts residents worried that they have seen Asian longhorned beetles inside their houses. In actuality, many of these reports turn out to be another ALB ‘look-alike’ species: the Western conifer seed bug (Leptoglossus occidentalis). This insect has a brown body about 3/4 of an inch long, alternating white and brown marks on its lower body surrounding the wings, and back legs that have a distinct flattened leaf-like shape (see photo). The Asian longhorned beetle, by contrast, has a very shiny black body with prominent white spots. Also, the antennae of the Western conifer seed bug are brown and lack the alternating black and white bands found on the antennae of ALB.

Unlike Asian longhorned beetles, which overwinter as wormlike larvae, deep inside hardwood trees, adult Western conifer seed bugs escape cold temperatures by seeking shelter in houses and other warm locations. At this time of year, you may find a Western conifer seed bug lurking around the foundation of your house, or buzzing around a window screen looking to escape the approaching autumn weather. If you have encountered this insect pest before, you may also have had the unpleasant experience of smelling the acrid, citrusy-smelling liquid it emits when startled.

Western conifer seed bugs are native to the west coast of the USA, but have been established on the east coast since the 1990s. Unlike ALB, a non-native and serious pest of hardwood trees, the Western conifer seed bug is only considered a minor pest of the coniferous trees they attack (pine, Douglas fir and hemlock). However, these bugs can be a major inconvenience if they find a way to enter your home. Small infestations can be handled by sealing up any crevices that the bugs could be using to sneak in (holes in screens, chimneys, loose window fittings, etc.) and by capturing escapees by hand or by shop vac. Larger infestations may require consultation with a licensed pest specialist.

To learn more about the Western conifer seed bug, read this fact sheet from Cornell University’s Insect Diagnostic Laboratory. To report a potential sighting of Asian longhorned beetle, click here.