The Western Conifer Seed Bug (Leptoglossus occidentalis) is a common, large insect that becomes a nuisance when it moves into homes during cooler months. These pests do not cause structural damage or pose health threats, but their presence can be alarming, especially when they appear in large numbers during autumn. They seek a safe, dry place to enter dormancy (diapause) to survive the winter. Managing an infestation requires immediate removal of bugs already inside and preventative measures to block future entry points.
Identifying the Western Conifer Seed Bug and Its Habits
Adult Western Conifer Seed Bugs are distinctively large, typically measuring about three-quarters of an inch in length. Their bodies are a dull brownish-gray color. A key identifying feature is the prominent, flattened, leaf-like expansion on the lower part of their hind legs. When flying, they produce a loud buzzing sound and reveal a yellowish-orange and black pattern on their abdomen beneath their wings.
These insects are primarily plant feeders, consuming sap from developing conifer seeds. They pose no threat to household goods or food stores once inside a home. Adults begin seeking sheltered overwintering sites in late summer and early fall, often congregating on sun-warmed exterior walls. They do not reproduce indoors, living off stored fat reserves until spring.
Immediate Indoor Removal Techniques
The most effective method for removing bugs already inside is vacuuming, but this must be done carefully to prevent releasing their defensive odor. Use a dedicated shop vacuum or a vacuum with a hose attachment. A critical modification is placing a knee-high nylon stocking or thin sock inside the collection tube or canister, secured with a rubber band, to create a removable filter.
The bugs are sucked into this filter and contained, allowing the user to remove the sock without the pests touching the main vacuum bag or filter. Once captured, the sealed sock can be discarded immediately outside, or the bugs can be drowned in soapy water. Avoid crushing the bugs, as their defensive glands release a pungent, pine-like odor that can linger on surfaces.
For a few isolated individuals, a simple hand-removal technique avoids odor release. Gently sweep the bug into a jar or container with a tight-fitting lid, or use tissue paper or a gloved hand to pick it up. The collected bugs can then be released outdoors, away from the home. Standard sticky traps or light traps are not effective for mass removal, as the bugs are not strongly attracted to them.
Structural Exclusion for Long-Term Prevention
The most reliable long-term solution involves mechanical exclusion: sealing all potential entry points into the structure before the overwintering migration begins. This work is most effective when completed during the summer months, ideally before late August or early September. The goal is to eliminate any gap wider than an eighth of an inch, which is enough space for the bugs to squeeze through.
Focus on sealing fixed gaps and cracks along the foundation, where different building materials meet, and around all window and door frames using quality exterior-grade caulk. Utility penetrations, including areas where wires, cables, and pipes enter the home, must be sealed with caulk or expanding foam. Inspect and repair any tears in window and door screens, as well as the fine mesh screening covering attic and foundation vents.
Attention should also be paid to the roofline, specifically the soffits and fascia boards, which often have small gaps leading into the attic or wall voids. Weep holes in brick veneers can be covered with fine wire mesh or specialized covers to prevent entry while still allowing moisture to escape. Attempting this sealing after the bugs have moved into the walls is counterproductive, as this traps them inside, forcing them to eventually emerge into the living space.
Exterior Population Management
For homes with heavy annual infestations, applying a residual insecticide to the exterior perimeter provides an additional layer of protection. This treatment should be timed for late summer or early fall, right when the adult bugs begin to aggregate on outside walls seeking entry. The insecticide creates a barrier that kills the insects as they crawl across the treated surface before they can find a gap.
Pesticides containing active ingredients from the pyrethroid class, such as permethrin or lambda-cyhalothrin, are commonly used for this type of barrier application. The spray should be directed toward the foundation, covering a band of one to three feet up the exterior wall and a few feet out onto the soil. It is also important to target the areas surrounding windows, doors, and under eaves, which are common congregation points.
Chemical application is primarily a preventative measure to manage the outdoor population attempting to enter the home. Indoor application of insecticides or foggers is ineffective for these pests, as they hide deep within wall voids and cracks, making direct contact impossible. Always read and follow the label directions on any pesticide product.