Stink bugs are a growing concern in Colorado, especially in fall when adults seek warm shelter inside homes. The state is home to both native stink bug species and the invasive brown marmorated stink bug, which damages fruit crops and garden plants. Whether you’re finding these shield-shaped insects on your windowsills or noticing damage in your garden, here’s what Colorado residents need to know.
Stink Bug Species in Colorado
The brown marmorated stink bug is the most problematic species in Colorado. Originally from East Asia, it’s an invasive pest that feeds on a wide range of fruiting plants, vegetables, and field crops. Adults are roughly 3/4 inch long with a mottled brown, shield-shaped body and distinctive white banding on their antennae.
Colorado is also home to several native stink bug species and a common lookalike: the western conifer seed bug. This insect is frequently mistaken for a stink bug, but it’s noticeably different up close. Western conifer seed bugs are about 3/4 inch long with dark brown wings that form a diamond shape on the back. Their most obvious feature is enlarged, leaf-shaped hind legs that stink bugs don’t have. They also have a long, pointed head that extends forward from the body. Both insects show up inside Colorado homes in fall, but the conifer seed bug feeds on pine seeds rather than garden crops.
Another insect sometimes confused with stink bugs is the assassin bug, which lacks the broad hind legs of the conifer seed bug and can actually bite. The western bloodsucking conenose is a much larger relative that rarely turns up in homes.
When and Why They Enter Homes
Adult stink bugs move toward buildings on warm, sunny days in September and October. They aren’t looking for food. They’re looking for a place to spend the winter. Once they land on an exterior wall, they crawl into any gap they can find: cracks around windows, doors, roof flashing, vents, window air conditioners, fascia boards, and siding. They tend to prefer upper areas of buildings, often entering through attics and chimneys.
Once inside walls or attic spaces, they enter a dormant state for the winter. On warmer days in late winter or early spring, some wake up and wander into living spaces, which is why you might see them indoors even in February or March. By that point, they’ve already been inside your home for months.
Damage to Gardens and Fruit
In the yard, stink bugs cause real problems for anyone growing fruit or vegetables. Both adults and immature nymphs use needle-like mouthparts to pierce plant tissue and extract fluids, injecting digestive enzymes in the process. On fruit, this feeding creates oozing sap and turns the flesh under the skin hard and pithy. Younger fruits that are fed on early in the season develop discoloration, disfiguration, and pockmarks as they mature.
Peaches and nectarines are especially vulnerable to early-season damage. For other fruit trees like apples, pears, plums, and grapes, damage tends to be worst on late-maturing fruit when stink bug populations peak in late summer. When densities are high, multiple adults may attack a single fruit. In vineyards, the defensive chemicals stink bugs release can actually taint grape juice and wine.
Beyond fruit, stink bugs also feed on buds, stems, leaves, branches, and seed pods. Leaf feeding creates small stippled spots about 1/8 inch across around each feeding site. The injuries from brown marmorated stink bugs look identical to those from native stink bug species, so identification of the insect itself is the only way to tell which species is responsible.
Are Stink Bugs Harmful to People or Pets?
Stink bugs don’t bite, sting, or transmit diseases. Their only defense is the foul-smelling chemical they release when threatened or crushed. For humans, the smell is unpleasant but harmless.
Pets are a slightly different story. Stink bugs aren’t poisonous, but dogs and cats that chew on or eat them may experience gastrointestinal irritation from those same defensive secretions. Symptoms include vomiting, excessive drooling, and irritation of the tongue, gums, lips, and inner cheeks. These effects are temporary and don’t appear to cause serious long-term health problems.
How to Keep Them Out
The most effective strategy is physical exclusion, and the timing matters. You need to seal entry points before stink bugs start gathering on buildings in early to mid-September. Once they’re already inside your walls, there’s no practical way to treat from the outside. Barrier treatments applied in late winter or spring are ineffective because the bugs gained entry months earlier.
Focus on these common entry points:
- Windows: Caulk gaps around window frames on both the interior and exterior. Inspect screens for tears or holes.
- Doors: Add weather stripping around entry doors and install door sweeps anywhere you can see daylight around the door perimeter.
- Foundation: Seal cracks and gaps in the foundation, and secure entrances to crawlspaces.
- Plumbing and utilities: Caulk small openings around exposed pipes and use appropriate filler materials for larger gaps.
- Roof and chimney: Cap or screen chimneys and fireplace openings. Check roof flashing and vent covers.
- Landscaping: Keep debris and edible vegetation away from your home’s foundation, which reduces the number of stink bugs congregating near entry points.
Removing Stink Bugs Already Inside
If stink bugs are already in your living space, remove them quickly. The simplest approach is to pick them up gently and release them outside, or vacuum them up. Be aware that crushing or vacuuming stink bugs can release their characteristic odor, though the smell will not attract more bugs into your home.
A simple homemade light trap works well for larger numbers. Fill a roasting pan with soapy water and place it in a dark room with a light directed at the water’s surface. Stink bugs are drawn to light and will fly into the soapy water, where they drown. This is an effective, chemical-free way to reduce indoor populations during those late-winter warm spells when overwintering bugs become active.
After removing any current invaders, the priority shifts to finding and sealing the entry points they used so the cycle doesn’t repeat next fall. Check around doors, windows, and foundation cracks carefully, since even small gaps are enough for these flat-bodied insects to squeeze through.