This time of year, reports sometimes come in through our ALB reporting form from Massachusetts residents worried that they have found Asian longhorned beetle inside their homes. Most of these reports turn out to be the Western conifer seed bug (Leptoglossus occidentalis or “WCSB”), which can be confused with Asian longhorned beetle. This insect has a dark 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 shiny black body, like patent leather, 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 sunning itself on the side of your house or buzzing around a window screen, looking to escape the approaching cool 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, which is a non-native and serious pest of hardwood trees, the Western conifer seed bug is only considered a minor pest of the coniferous trees it attacks (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. To report a potential sighting of Asian longhorned beetle, click here. To see a gallery of ALB Look-alikes, download our guide.