Over the past few weeks I’ve seen three nymph stages of the Western Conifer Seed Bug (Leptoglossus occidentalis), or WCSB. These colorful, strutting youngsters become handsome adults and they have an interesting life story.
First off, female WCSBs lay rows of brown eggs on pine needles. When the first-stage bugs emerge, they stay true to the “conifer seed” portion of their name and feed on the soft parts of early pine cones. The feeding doesn’t hurt the tree, but it may reduce the number of seeds a tree produces.
Nymphs, also called “instars,” go through five stages of growth, shedding an exoskeleton and donning a new signature style each time. The instars sport various shades of red and orange, with button-like markings on their abdomens. WCSB’s don’t have wings until they’re adults, so they use their spiny, color-warning look to intimidate predators.
Most sources I found said there is one generation of Leptoglossus occidentalis per year, and they become adults by August or September. So why am I seeing nymphs in October? I put the question to the helpful folks at BugGuide and am awaiting an answer.
The adults are fairly common this time of year. You might see them on the sides or windows of houses. Like many true bugs, adult WCSBs live through the winter and as temperatures fall, they seek more comfortable places to spend the season.
Leptoglossus occidentalis are in the Coreiidae family, also known as “leaf-footed” bugs. They can discharge a scent from between the last two pairs of legs if they’re disturbed. Several sources describe it as a pungent pine smell. Well, if you’d been consuming pine products and living among them your entire life, you’d probably smell that way too!
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Wisconsin Horticulture Extension page: https://hort.extension.wisc.edu/articles/western-conifer-seed-bug/. Accessed 10/18/22.
Penn State Extension page: https://extension.psu.edu/western-conifer-seed-bug. Accessed 10/18/22.