Are Those “Stink Bugs” in Your Home?

Since September, I have been awakened from a dead sleep countless times by an obnoxious buzzing in my ear and, even more unsettling, the feeling that something is crawling on top of my head. Although groggy, I usually realize pretty quickly that it’s just a stink bug, grab it, and toss it across the room. Admittedly, this method of disposal did backfire once when the stink bug turned out to be a paper wasp; a regrettable mistake.

So what are these annoying insects? Why are they in our homes?

 Consperse stink bug
Figure 1. The Consperse stink bug (Euschistus conspersus) Photo: Mike Quinn, Bugguide.net

You may be surprised to find out that these insects are not actually stink bugs. Stink bugs are in the family Pentatomidae and have bodies shaped like shields (Figure 1). The insect in question is actually in the family Coreidae, or the leaf-footed bugs. The common name “leaf-footed” refers to the enlarged leaf-like structure on their hind legs (Figure 2). The genus and species of this particular leaf-footed bug is Leptoglossus occidentalis whose common name is the western conifer seed bug (WCSB).

Although you may be familiar with the WCSB because of its presence in your house, this insect is actually a forest dweller. The WCSB feeds on seeds, developing cones and the needles of pine trees, as well as Douglas-fir.

Western conifer seed bug
Figure 2. The Western conifer seed bug; notice the leaf-like structure on the hind legs. Photo: Bugguide.net

The WCSB has a single generation a year. Adults emerge in late May or early June. At this time, they feed on one-year-old cones and inflorescences (small flower clusters). Eggs are laid in rows on conifer needles and hatch within 10 days. The WCSB is a “true” bug in the order Hemiptera and does not go through complete metamorphosis as a fly or butterfly would. In other words, there is no larval stage. Instead, the young look very similar to the adults, only smaller, and are called nymphs rather than larvae (Figure 3).

The WCSB goes through five nymphal instars (stages) prior to the final adult stage. The first instar feeds on needles and cone scales while older nymphs will feed on developing seeds. The WCSB reaches adulthood around mid-August and will continue to feed on ripening seeds until early fall, after which time it will begin to seek overwintering sites. This is when you may begin seeing them in your home. The WCSB will overwinter under bark, in dead and dry logs, in bird and rodent nests, and of course, in buildings. With its flattened body shape, it can enter a house through most small openings. Once inside the house, they tend to become active and conspicuous when warm.

Nymphal stages and final adult form of the Western conifer seed bug
Figure 3. Two nymphal stages (on the left) and the final adult form (far right) of the Western conifer seed bug. Photo: Brandon Woo

Although annoying, the WCSB is not harmful to people. It does not bite, sting, eat wood, or breed indoors. It does emit an unpleasant odor when disturbed, but this is not harmful to anything but our noses. The tendency to think that WCSB is harmful may be due to a case of mistaken identity, as leaf-footed bugs have a similar appearance to assassin bugs (family Reduviidae), which do bite. There are morphological differences that distinguish WCSB from assassin bugs; the most obvious is the leaf-like structure found on the hind legs of the seed bug, which assassin bugs lack (Figure 4).

Assassin bug
Figure 4. Assassin bug Sinea diadema; notice the lack of the leaf-like structure on the hind legs, which the Western conifer seed bug possesses. Photo: Michael Hughes, Bugguide.net

The WCSB can be a pest to the forest industry, particularly in seed orchards, as it can result in a substantial loss of seed crop. However, in a general forested setting, there are typically plenty of seeds to go around and there is no lack of regeneration in our forests as a result of these bugs.

So, is there any way to control the WCSB? The best method of control is prevention via mechanical exclusion. This of course would involve filling in any cracks around the house where they may be getting in. Replacing loose screens, windows and doors; caulk gaps; and screen your fireplace, attic and wall vents, and other openings — basically, blocking all points of entry. Unfortunately, if your house is anything like mine, this is a near impossible endeavor. I opt for the vacuum cleaner and just suck them up.

By Melissa Fischer, forest health specialist, Washington State Department of Natural Resources, Northeast Region, melissa.fischer@dnr.wa.gov