The brown marmorated stink bug (Halyomorpha halys) is a shield-shaped insect native to East Asia that has become a significant agricultural and nuisance pest worldwide. First documented in the United States in the late 1990s, this insect feeds on a wide variety of fruits, vegetables, and ornamental plants, causing substantial crop damage. The pest is well-known for its defensive mechanism that releases a foul odor when disturbed or crushed. While this defense makes it a difficult target, stink bugs do have predators, though effective control often requires specialized hunters.
The Chemical Defense That Deters Predators
The characteristic malodor that gives the stink bug its name is a highly effective chemical defense system against generalist predators. This pungent odor is produced and stored in specialized glands located on the underside of the insect’s thorax. When the stink bug feels threatened, it releases a blend of volatile organic compounds through these glands.
The primary compounds responsible for the smell are aldehydes, specifically trans-2-decenal and trans-2-octenal. These chemicals are irritating and unpalatable, immediately signaling to a potential predator that the insect is not a worthwhile meal. This chemical cocktail functions as a deterrent, causing birds, small mammals, and most generalist insects to drop the stink bug or avoid it entirely after a single encounter. Because the mechanism is designed to prevent consumption, generalist hunters rarely make a sustained impact on stink bug populations.
Specialized Foes: Parasitic Wasps and Flies
The most effective natural enemies of the stink bug are highly specialized parasitoids that bypass the adult’s chemical defense by targeting the egg. These tiny insects, often less than two millimeters in length, evolved alongside the stink bug in its native range. This gives them a distinct advantage over native predators in newly invaded areas and offers the most promising route for natural population control.
The most notable of these specialized foes is the Samurai Wasp, Trissolcus japonicus. The female wasp locates an egg mass—typically laid on the underside of a leaf—and lays her own egg directly inside a host egg. The wasp larva then develops internally, consuming the developing stink bug embryo as its food source.
The wasp completes its development inside the stink bug egg, eventually emerging as an adult wasp that chews a small, circular exit hole through the eggshell. In its native East Asia, the Samurai Wasp is highly effective, capable of parasitizing up to 80% of egg masses, which significantly limits the pest’s population growth. This specialization demonstrates how one species has adapted to overcome the chemical defenses of the other.
Generalist Hunters That Still Try
Despite the powerful chemical defense, a variety of generalist predators still attempt to consume stink bugs, often when the prey is particularly vulnerable. Birds, for example, have been observed eating stink bugs, especially chickens and turkeys, which may be less deterred by the foul taste than wild songbirds. These animals are opportunistic hunters that consume the pests, but they are not efficient population control agents.
In the insect world, some generalist predators attack the less-defended egg and nymph stages.
Insect and Mammal Predators
Various spider species, including the invasive Joro spider, and predatory insects like the wheel bug (Arilus cristatus) prey on stink bugs. The wheel bug uses a piercing-sucking mouthpart to inject paralyzing saliva, quickly overcoming the pest before it can release its full chemical defense. Small mammals, such as bats and shrews, also include stink bugs in their diet when other food sources become scarce.