The Brown Marmorated Stink Bug (Halyomorpha halys) is a shield-shaped insect known for appearing indoors and releasing a pungent odor when disturbed. Native to Asia, this invasive species is now widespread across North America and Europe. Homeowners often encounter them late at night and question whether these bugs pose a threat by biting humans. Understanding the insect’s biology clarifies its threat level, which is more of a nuisance than a danger.
The Answer to the Biting Question
The definitive answer is that the Brown Marmorated Stink Bug does not bite humans. These insects are “true bugs” (order Hemiptera) and possess specialized mouthparts called a proboscis, designed for piercing and sucking. This rigid, straw-like structure is not capable of tearing or chewing flesh.
The mouth structure is adapted exclusively for feeding on plants, not mammal flesh or blood. They use the proboscis to pierce the outer layers of fruits, vegetables, and leaves, sucking out internal plant fluids. This feeding method makes them a significant agricultural pest, damaging crops like apples, peaches, and soybeans.
While they cannot bite defensively, accidental “poking” can occur if the insect lands on a person and mistakes the skin for a plant surface. This is not an attempt to feed, and the mouth structure is typically not strong enough to pierce human skin. Any sensation felt would be a minor prickle, not a true bite, and they do not transmit diseases to people or pets.
Understanding Their Defensive Odor
The most common interaction people have with this insect is the unpleasant smell that gives the bug its name. This odor is a chemical defense mechanism intentionally released when the bug is physically threatened or crushed. The secretion originates from scent glands located on the underside of their thorax.
The smell is a potent mixture of chemical compounds, primarily aldehydes, specifically trans-2-decenal and trans-2-octenal. These aldehydes create a pungent odor often characterized as smelling like cilantro, burnt rubber, or a strong, musky spice. The purpose of this chemical release is to deter predators, such as birds or spiders.
Beyond being a deterrent, these aldehydes also possess an antimicrobial function, offering the insect protection against fungi and bacteria. The lingering nature of the odor is due to the composition of these chemicals, which are designed to persist in the environment. This defensive release is the primary reason why homeowners are advised to vacuum up the insects rather than crushing them.
Why They Seek Indoor Shelter
The reason these insects are often encountered inside homes is their need to find a sheltered spot for the winter. The Brown Marmorated Stink Bug is an overwintering pest, entering a state of dormancy called diapause to survive the cold months. This process is triggered by the shortening daylight hours (photoperiod) in the late summer and early fall.
As temperatures begin to drop, the adults start aggregating and migrating from their outdoor feeding sites toward warm, protected structures. They seek out crevices in buildings, preferring high-up, dry locations like attics, wall voids, and spaces around window and door trim. They remain in this state of reproductive arrest and metabolic suppression throughout the winter.
These bugs become visible inside the living space when fluctuations in indoor temperature or sunlight rouse them from their dormant state. A sudden warm spell or the warmth emanating from within a house can cause them to become temporarily active. This is why they are frequently found crawling on walls or flying toward lights at night, as they have emerged from their hidden overwintering sites.