The Brown Marmorated Stink Bug (Halyomorpha halys) is an invasive insect that has become a widespread household pest, particularly in North America and Europe, since its accidental introduction from Asia in the mid-1990s. This shield-shaped insect is known for invading homes in large numbers during cooler months and emitting an unpleasant odor when disturbed. Understanding the stink bug’s behavior and defense mechanisms is important for managing its nuisance presence.
Identifying the Brown Marmorated Stink Bug
The adult Brown Marmorated Stink Bug (BMSB) is easily recognizable by its distinct shield shape, measuring roughly 1.7 centimeters (about half an inch) in length. Its coloring is generally a mottled dark brown or gray, giving it a marbled appearance. A defining feature is the alternating light and dark bands found on the last two segments of its antennae and along the thin outer edge of its abdomen.
The bug’s behavior is strongly tied to seasonal temperature changes. As autumn evenings become colder, adult stink bugs look for protected sites to enter a state of dormancy known as overwintering. They congregate on the outsides of buildings and seek entry through small cracks, gaps, utility openings, and under siding. Once inside, they remain inactive, neither feeding nor reproducing, until warmer spring temperatures prompt them to emerge.
Do Stink Bugs Pose a Physical Threat to Humans
The Brown Marmorated Stink Bug does not pose a physical threat to humans or pets. Stink bugs are herbivores, meaning their mouthparts are specifically adapted for feeding on plants. They possess a specialized piercing-sucking mouthpart called a proboscis, which they use to pierce plant tissue and suck out juices, causing damage to crops and fruit.
These insects are not venomous and do not transmit diseases to humans. In extremely rare instances, a stink bug may accidentally “probe” human skin if confused or seeking moisture, but this action is negligible and is not a true bite. The fluid released when a bug is crushed can cause mild irritation or dermatitis upon contact for those with sensitive skin. This reaction is due to the chemical defense, however, and the worst outcome of a physical interaction is the release of their pungent defensive odor.
The Mechanism of Their Defensive Odor
The odor that gives the stink bug its name is a potent chemical defense mechanism designed to deter predators. The bug stores and releases this chemical cocktail from specialized scent glands located on the underside of its thorax and abdomen. This secretion is released when the insect is crushed, handled roughly, or feels threatened.
The defensive spray is primarily made up of aldehydes and hydrocarbons. The major alarm compounds in the Brown Marmorated Stink Bug are two aldehydes: trans-2-octenal and trans-2-decenal. Aldehydes contribute a sharp, pungent scent, while hydrocarbons help the odor linger and increase the deterrent’s effectiveness. The smell is often described as a pungent, herbaceous odor, sometimes compared to coriander or strong cilantro.
This chemical defense serves a multifunctional role. The compounds exhibit antibacterial and antifungal properties, which helps protect the insect’s body from microbial infection. Furthermore, the release of these compounds acts as an alarm signal, warning other nearby stink bugs of danger.
Practical Methods for Removal and Prevention
Safe removal methods focus on mechanical action without crushing the insect, as disturbing them triggers their chemical defense. One effective technique for removing bugs already inside is to use a vacuum cleaner. A dedicated shop vacuum is recommended to prevent the odor from permeating a household unit. After vacuuming, the contents should be immediately sealed and disposed of outside to prevent the trapped bugs from crawling out or releasing their odor.
Another simple removal method involves a container of soapy water. Since the bugs tend to drop straight down when disturbed, a jar or bucket filled with water mixed with dish soap can be held beneath the bug, causing it to fall in and drown. The soapy solution breaks the surface tension of the water, preventing the bug from escaping.
Preventing entry is the most effective long-term strategy. Since they enter structures through small openings, sealing all potential entry points is necessary before cooler weather arrives. Homeowners should take the following steps to exclude the insects:
- Use a good quality caulk to seal cracks around window frames, door frames, utility pipes, and electrical outlets.
- Replace or repair damaged window and door screens.
- Ensure chimney and attic vents are properly screened with fine mesh.