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How to identify it
- Adults are reddish brown to dark brown. Penn State and Wisconsin give 3/4 inch long, Colorado State 5/8 to 3/4 inch and Montana State 1/2 to 3/4 inch.[1][5][2][3]
- The hind legs have flattened, leaf-like widenings on the lower segment, which gives the leaf-footed bug family its name.[1][2][5]
- A thin, jagged white line often crosses the back (it can be darker or missing), the membranous wing tips form a dark diamond at the rear, and patches of yellow or light orange alternate with black along the edges of the abdomen.[1][5]
- In flight they make a loud buzz and show a bright yellow-orange and black abdomen, which can make them look like a bee.[1][5]
- Young nymphs are orange and turn reddish brown as they grow. Eggs are about 2 mm (0.08 inch) long, laid in chains on conifer needles.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Brown marmorated stink bug | Because of its piney odor the seed bug is sometimes called a stink bug, but true stink bugs have a broad, shield-shaped body rather than a long, narrow one.[2][5] |
| Kissing bugs and other assassin bugs | Assassin bugs lack the widened hind legs, often have thicker front legs, and carry a pointed beak projecting from the head; unlike seed bugs, they can bite. Montana State notes the seed bug is often mistaken for a kissing bug.[2][3][5] |
| Squash bug | A garden pest of squash in the same family that lacks the flared, leaf-like widenings on the hind legs.[1][2] |
| Magnolia leaf-footed bug | Plain brown without patterning, with prominent toothed shoulders, and it specializes on magnolia seed pods.[1] |
| Other Leptoglossus seed bugs | The leaf-footed pine seed bug (L. corculus) is darker brown with an all-black abdomen; the eastern leaf-footed bug (L. phyllopus) has thicker white lines and larger, more scalloped leg flaps; the western leaffooted bug (L. clypealis) has a spine at the front of the head and usually feeds on junipers.[1][2] |
Where it lives
Native to the Pacific Coast of western North America, it spread east from the 1950s and now occurs across the United States and southern Canada, most abundantly in the Northeast.[1]
Biology and life cycle
Hosts include various pines, spruces, hemlocks and Douglas-fir. Wisconsin lists white, red, Scots, Austrian and mugo pine, white spruce, Douglas-fir and hemlock, and Colorado State adds developing seeds of dogwood and sumac.[1][5][2]
There is one generation a year in North America (Penn State says up to three in more tropical areas such as Mexico). Adults leave winter shelter in late May to early June and feed on year-old cones and male flowers.[1][2][3][5]
Females glue small rows or groups of eggs to conifer needles; eggs hatch in about 10 days.[1][2][3]
Nymphs pass through five stages, feeding on developing seeds through summer, and reach adulthood in August and September.[1][2]
In fall, adults move to protected places such as loose bark, bird and rodent nests, under siding and into homes, where they stay semidormant, neither feeding nor reproducing, and live off fat reserves. Montana State says most don't survive the winter, and Colorado State says bugs indoors usually die in a week or two without water.[1][2][3]
Damage and signs
- They don't breed indoors or damage household items.[2][3][5]
- Seed feeding can destroy up to 80% of a seed crop in conifer seed orchards, but it doesn't harm the health of ornamental pines or Douglas-fir in yards.[1][3][5]
- In one rare case, the bugs punctured holes in cross-linked polyethylene plumbing tubing.[3]
- How many come indoors varies; Montana State says it depends on whether several conifers grow next to the house.[3]
Health risk
They feed on plants and are not considered a medical risk. A single bite has been recorded worldwide, described in a 2017 Journal of Medical Entomology report; Penn State says it was likely a mistaken feeding probe and left a red, itchy patch about 1 inch across that stopped itching after 48 hours and faded within 4 weeks without treatment. The same report notes that among true bugs, only the blood-feeding kinds (such as kissing bugs and bed bugs) have real medical importance.[1][6][3]
Control
Keep them out
Keeping them out is the best control: repair loose screens, windows and doors, and caulk gaps around frames, soffits, fascia and chimneys.[1][3][5]
Screen attic and wall vents and fireplace chimneys, and finish sealing in late summer, since most bugs move to buildings in September and October.[1][2][5]
Traps and physical control
Vacuum, swat or hand-remove bugs that get inside; don't use insecticides on insects already in the home.[2][3][5]
Pesticides
For bugs clustered on outside walls in fall, Wisconsin says insecticidal soap or general insecticides can be used, and Colorado State expects exterior crack-and-opening treatments to help, though it notes insecticides haven't been tested against this insect.[5][2]
Common questions
- Do western conifer seed bugs bite or sting?
- They don't sting, and Colorado State and Wisconsin say they don't bite. Only one bite has ever been documented worldwide, and it caused a mild, itchy red patch.[2][5][1][6]
- Why do they smell when I pick them up?
- When disturbed they give off a defensive odor from well-developed scent glands that many people describe as piney, which is why they get mistaken for stink bugs.[2][5]
- Why do I still see them in winter?
- Bugs sheltering in walls stay semidormant, but small numbers wander out on warm days in winter, and larger numbers on warm fall and spring days.[1][3][5]
- Where did they come from?
- They are native to the Pacific Coast of western North America and spread east from the 1950s, reaching Pennsylvania by 1992. Trade has since carried them to Europe, Asia, South America, South Africa and Australia.[1][6]
Sources
- Penn State Extension, “Western Conifer Seed Bug (updated January 19, 2026).” extension.psu.edu/western-conifer-seed-bug (accessed 2026-11-11)
- Colorado State University Extension, “Conifer Seed Bugs (Fact Sheet 5.588).” extension.colostate.edu/resource/conifer-seed-bugs/ (accessed 2026-11-11)
- Montana State University Extension, Schutter Diagnostic Lab, “Western Conifer Seed Bug (fact sheet, November 2022).” urbanipm.montana.edu/entomology/resources/fact-sheets/nuisance_insect_pests/western.conifer.seedbug.html (accessed 2026-11-11)
- iNaturalist, “Leptoglossus occidentalis taxon page (order and family).” www.inaturalist.org/taxa/67771 (accessed 2026-11-11)
- University of Wisconsin-Madison Extension, Wisconsin Horticulture, “Western Conifer Seed Bug (P. Pellitteri, UW Insect Diagnostic Lab, XHT1052).” hort.extension.wisc.edu/articles/western-conifer-seed-bug/ (accessed 2026-11-11)
- Journal of Medical Entomology, via PubMed, “Hornok S, Kontschan J (2017), The western conifer seed bug (Hemiptera: Coreidae) has the potential to bite humans, Journal of Medical Entomology 54(4):1073-1075.” pubmed.ncbi.nlm.nih.gov/28399275/ (accessed 2026-11-11). Cited from the PubMed abstract.