The brown marmorated stink bug, Halyomorpha halys, is a common pest native to Asia that was accidentally introduced to the United States in the mid-1990s. It has since spread widely, becoming a nuisance in homes and gardens. Its presence concerns both homeowners and farmers because it feeds on a broad range of plants and aggregates indoors during cooler months. Learning the specific visual cues for this insect is essential for management.
Key Physical Identifiers
The adult brown marmorated stink bug is recognizable by its distinctive pentagonal, or shield-like, body shape. These medium-sized insects typically measure about 1/2 to 3/4 inch (14 to 17 mm) in length. Their coloration is mottled brown and gray, giving them a marbled or “marmorated” appearance that provides excellent camouflage.
The most reliable identifying features are found on the antennae and the edge of the abdomen. The antennae display alternating bands of light and dark color, particularly noticeable on the last two segments. Along the outer edge of the abdomen, known as the connexivum, alternating light and dark bands are visible even when the wings are folded.
Stink bugs are “true bugs” and possess a piercing-sucking mouthpart, which appears as a thin, dark beak extending backward between the legs. They use this proboscis to pierce plant tissues and extract fluids, causing damage to fruits and vegetables.
Distinguishing Stink Bugs From Similar Insects
The shield-like shape is common, leading to frequent confusion with other species, but specific details allow for accurate identification. Squash bugs, often found on squash and pumpkin plants, also have a hard, shield-like body and brown coloration. However, the squash bug’s body is more elongated and narrower, and it lacks the alternating light and dark bands on the antennae characteristic of the brown marmorated species.
The Box Elder Bug is another insect often mistaken for the stink bug, though their appearance is quite different. Box Elder Bugs have an oval body shape and are easily distinguished by their striking black color with prominent red or orange markings. While they also seek shelter indoors in the fall, their coloration and shape make them visually distinct from the mottled, broad stink bug.
Native shield bugs, which are close relatives, can be more challenging to differentiate, but their coloring is more uniform. The Green Stink Bug is a solid, bright green. Other brown native species lack the unique white banding on the antennae and the distinct black and white striping around the abdominal margin. The smooth, rounded “shoulders” of the brown marmorated species also contrast with some native shield bugs that have sharp, pointed projections on the thorax.
Where and When You Find Them
The presence of these insects is tied to the seasons and their life cycle. During spring and summer, adult bugs are primarily outdoors, feeding on a wide variety of host plants, including trees, shrubs, and agricultural crops. They use their mouthparts to feed on reproductive structures like fruits, seeds, and pods, causing plant damage.
The most noticeable period for human encounter is in early autumn as temperatures cool. Adult stink bugs seek sheltered places to enter a state of dormancy, known as diapause, to survive the winter. They aggregate on sunny, exterior walls before crawling into cracks, crevices, and utility entry points to gain access indoors.
Once inside, they move into secluded areas like attics, wall voids, and behind baseboards, remaining inactive throughout the winter. They do not reproduce or feed while overwintering. However, they may become active and emerge into living spaces on warmer winter days or during the spring when attempting to exit the structure.
Understanding Their Defensive Odor
The insect earns its name from a potent chemical defense mechanism activated when the bug feels threatened or disturbed. The unpleasant odor is released from specialized glands located on the underside of the thorax. This chemical release is a survival strategy designed to deter predators such as birds and spiders.
The smell is a mix of chemical compounds, specifically trans-2-decenal and trans-2-octenal, which are volatile aldehydes. This combination is described as acrid, pungent, or sometimes compared to the strong scent of cilantro or coriander. The odor can be released by handling or crushing the bug, and the smell may linger in the air or on surfaces.