Western conifer seed bugs (WCSB) are an overwintering pest that lives outside during the summer and feeds on pinecones. In the fall, they enter structures for protection against the cold and desiccating wind. Like other overwintering insects, they do not build a nest indoors or cause structural damage, but rather hide in cracks and crevices. They may be seen on warm winter days near windows during the day and lights at night.
These ‘true bugs’ have sucking mouthparts and the often-seen triangular ‘shield’ where wings overlap near the thorax (segment between the head and the body) and dark “X” across the back. This true bug is long, fairly good-sized (3/4”) mottled dark browns in color, with fancy flairs on the hind legs. Look for the checkerboard/stripey dark/light markings along the outer sides of the body. Adult females lay chains of eggs that are each less than 1/10” on conifer needles. The nymphs (immature bugs) go through five developmental stages, starting out orange and gradually darkening to reddish brown.
While a heavy presence of WCSB can damage conifer seeds, their habit of overwintering inside homes makes them a nuisance. These insects do not bite or sting and so far, there’s no evidence they cause allergic reactions. They do not carry disease, but no one likes the strong, lingering odor emitted when they are disturbed. They are not stink bugs but they can stink!
Adults and nymphs feed on conifer seeds (think pine cones), so your chance of having them around ties into the nearby landscape. You may never see them on trees, but you will notice them when they gather to overwinter inside structures such as houses, or are active indoors during the winter. They are adept at finding entry through any gap in siding, eaves, and openings around doors and windows. Their noisy, bumbling flight inside your home make them hard to miss.
Reduce indoor invaders by replacing damaged or old screens; sealing gaps around doors and door frames, window frames; and using appropriate screening or mesh on soffits, chimneys and vents, including roof ridge vents. Consult the US Department of Energy Guideline for Durable Attics for more information. Seal gaps at the roof edge, along fascia and wherever utilities like cable wires enter the structure. Inside, seal gaps around light fixtures leading into attic spaces. Insecticide sprays on the outside of the house are costly and rarely effective, and useless indoors. Using a vacuum to collect a large group is effective, but they will leave an odor inside the vacuum cleaner. Collect them by hand in containers (knock them into soapy water) and dispose of them. Overwintering insects inside structures often die before spring leaving behind their bodies, which may attract and feed other incidental pests, such as carpet beetles and silverfish.