The Brown Marmorated Stink Bug (Halyomorpha halys) is an insect common in North America, originally introduced from Asia. This shield-shaped pest is often found in homes during cooler months as it seeks shelter for overwintering. It is notorious for a powerful defensive mechanism. When disturbed, the insect releases a highly volatile chemical secretion, a natural warning signal synonymous with the species.
The Distinctive Sensory Experience
The odor released by a threatened stink bug is pungent, sharp, and acrid. Many people describe the smell as having a metallic or bitter-sweet quality. The intensity of the odor is surprising, often lingering for hours, especially if the secretion contacts fabrics or porous surfaces.
The most frequently cited comparison for the common Brown Marmorated Stink Bug’s smell is the herb cilantro or coriander. This similarity means the unpleasant scent is often referred to as “coriander-like” in scientific literature. Other descriptive accounts include notes of burnt rubber, a waxy aroma, or a hint of paint thinner, highlighting the chemical complexity of the release.
The Chemical Composition of the Secretion
The notorious smell originates from volatile organic compounds (VOCs) produced within the insect’s body. The primary components are aldehydes, specifically trans-2-decenal and trans-2-octenal. These compounds create the potent and penetrating nature of the defensive spray.
The compounds are synthesized and stored within specialized scent glands located on the underside of the thorax, between the first and second pair of legs. The insect releases the chemicals onto a rough patch of its exoskeleton called the evapatorium. The evapatorium’s surface texture helps the liquid quickly evaporate, ensuring the foul scent spreads rapidly.
Why and When Stink Bugs Release Their Odor
The fundamental purpose of the secretion is to act as a defensive mechanism against predators. The foul smell serves as a warning signal, making the insect an unappetizing meal for birds, lizards, and other natural enemies. The odor is repellent and tastes extremely bad, causing predators to immediately spit the bug out.
The release of the odor is not continuous; stink bugs control when the chemicals are deployed. The secretion is typically triggered by an immediate physical threat or disturbance, such as being crushed, jostled, or roughly handled. Beyond defense, the chemicals have a secondary benefit, exhibiting antimicrobial and antifungal properties.