Western conifer-seed bug, Leptoglossus occidentalis
The western conifer-seed bug is a common household nuisance in the fall and winter. These insects are harmless but can produce an unpleasant pine-like odor when disturbed. Adults are 19 mm (3/4 inch) in length and have red or dark brown bodies with white or yellow stripes on the abdominal margins. A notable feature of the western conifer-seed bug is the large hind legs. In addition, the second segment of the hind legs (tibia) are often leaf shaped. Their wings are dark brown and form a diamond shape at the end of the abdomen. The western conifer-seed bug has eyes on either side of the head, and the head extends from the insect’s body in a long, pointed protrusion. When in flight, they produce a loud buzzing sound and the rest of the abdomen is visible, which ranges from yellow to orange in color, often with black markings. This behavior along with the abdominal coloration is believed to mimic bees as an anti-predation strategy. Nymphs are smaller than adults, do not fly, and are black with a yellow or orange abdomen.
Other insects that are commonly mistaken for the western conifer-seed bug include squash bugs (Anasa tristis), assassin bugs (Family Reduviidae), and the western blood-sucking conenose (Triatoma protracta). Squash bugs are common in gardens of Colorado but do not commonly enter homes. Unlike the western conifer-seed bug, assassin bugs do not have broad hind legs and are predators that can bite. The western bloodsucking conenose is much larger than the western conifer-seed bug and is uncommon in households.
- Western conifer-seed bugs are typically found in homes during the colder months. While they are loud fliers that emit an unpleasant odor when disturbed, these insects are harmless.
- Adults have enlarged hind legs with a broad second segment (tibia) that resembles a leaf. Insects likely to be confused with this pest include the squash bug, assassin bugs, and the western bloodsucking conenose.
- Management tactics include sealing cracks and crevices, physical removal of insects found in the home, and in some cases, insecticide applications on the exterior of potential entry sites.
Adult western conifer-seed bug. Note the eyes on either side of the pointed head, large hind legs, and white stripes on the abdominal margins. Image credit: Dawn Dailey O’Brien, Cornell University, Bugwood.org
Immature western conifer-seed bug. Note the black bodies and orange abdomens. Image credit: Sandy Kegley, USDA Forest Service, Bugwood.org
Life history and habits
The western conifer-seed bug has three life stages: egg, nymph, and adult. Western conifer-seed bugs overwinter as adults. Adults seek overwintering shelter in September through November when they enter homes, garages, or sheds.
In late May, females lay small groups of eggs on needles and leaves of pines, Douglas-fir, and other conifers. They spend summer as nymphs, developing through five instars while feeding on seeds of pines and Douglas-fir before maturing into adults at the end of summer. Adults continue feeding until temperatures drop in the fall. One generation is produced each year.
Jacobs, S. 2023. Western Conifer Seed Bug. Penn State Extension. Available https://extension.psu.edu/western-conifer-seed-bug
Utah State University. (n.d.). Western Conifer Seed Bug. Utah State University – Extension. Available https://extension.usu.edu/pests/schoolipm/structural-pest-id-guide/western-conifer-seed-bug
Western Conifer-Seed Bug. (n.d.). Cornell – College of Agriculture and Life Sciences. Available https://cals.cornell.edu/new-york-state-integrated-pest-management/outreach-education/whats-bugging-you/western-conifer-seed-bug#:~:text=Western%20conifer%20seed%20bugs%20are%20often%20confused%20with%20brown%20marmorated,but%20are%20longer%20and%20narrower.&text=Adult%20females%20lay%20chains%20of,%2F10”%20on%20conifer%20needles.&text=The%20nymphs%20(immature%20bugs)%20go,gradually%20darkening%20to%20reddish%20brown