The Brown Marmorated Stink Bug (Halyomorpha halys) emerged as a significant agricultural and household pest. This invasive insect is highly damaging, feeding on over 100 plant species, including commercially important fruits and vegetables. It is also a major nuisance pest when it seeks shelter indoors for the winter. The species has flourished because its specialized defensive mechanism makes it an unappealing target for most local predators. This chemical deterrent means few native animals consistently consume the adult bugs, contributing to the pest’s rapid population growth.
The Role of Specialized Insect Predators
The most effective natural checks on stink bug populations come from specialized insect enemies, primarily tiny parasitic wasps. These wasps, known as egg parasitoids, circumvent the adult bug’s chemical defenses by attacking its stationary egg masses. The female wasp deposits her own eggs inside the stink bug eggs, and the developing wasp larva consumes the host embryo, preventing the pest from hatching.
The most notable of these specialized predators is the Trissolcus japonicus wasp, commonly called the samurai wasp. This minute wasp, only one to two millimeters long, can achieve parasitism rates as high as 90% in its native environment, making it a powerful biological control agent. Generalist arthropod predators also contribute to control, particularly against the more vulnerable nymph and egg stages. Spiders, including active hunters like wolf spiders and web-building orb-weavers, frequently ensnare and consume both young and adult stink bugs. Predatory insects, such as the spined soldier bug and assassin bugs, will also pierce the body of a stink bug nymph to consume its internal fluids.
Vertebrate Animals That Consume Stink Bugs
A variety of vertebrate animals will consume stink bugs. Birds are among the most frequent vertebrate consumers, with species like bluebirds, robins, and cardinals eating the pests, especially during nesting season when they require protein-rich food for their young. Larger birds, such as crows and ravens, have also been observed feeding on adult stink bugs when other food sources are scarce.
Consumption by these animals suggests they either tolerate the noxious taste or are able to consume the insect quickly, minimizing exposure to the defensive compounds. Small mammals, including shrews and mice, have also been documented preying on stink bug egg masses found on the ground or within leaf litter. Amphibians, like frogs and toads, also consume stink bugs, relying on their sticky tongues and rapid swallowing to capture and ingest the prey before the defensive chemicals can fully deploy.
How Stink Bugs Deter Predators
The infamous odor produced by stink bugs is a sophisticated chemical defense designed to elicit immediate predator rejection. This noxious secretion is deployed from specialized thoracic glands and is primarily composed of short-chain aldehydes and hydrocarbons. The compounds trans-2-octenal and trans-2-decenal are the major components responsible for the pungent scent.
Upon feeling threatened, the bug releases a droplet of this volatile mix. This acts not to kill the predator but to create a foul taste and smell. This potent chemical signal teaches generalist predators to associate the stink bug’s appearance with an unpleasant, non-lethal experience, ensuring they seek less offensive prey in the future.
Supporting Natural Stink Bug Control
Homeowners and gardeners can support the natural enemies of stink bugs by implementing habitat management strategies. A primary action is to avoid the use of broad-spectrum insecticides, which indiscriminately kill the beneficial parasitic wasps and generalist predators. Allowing native wasps and spiders to thrive is the best long-term control method.
Planting native flora and maintaining a diverse garden environment provides necessary resources and shelter for beneficial insects, including the samurai wasp. Certain plants, such as French marigolds, buckwheat, and purple tansy, are known to attract parasitic wasps, encouraging them to remain in the area. Keeping garden areas clean of debris and overwintering sites, such as leaf litter, helps reduce the number of adult stink bugs that survive the winter.