Box elder bugs (Boisea trivittata) are common insects found around homes and on box elder, maple, and ash trees, particularly as cooler weather approaches, where they feed on seeds and foliage. Understanding their appearance at different life stages aids identification.
Adult Box Elder Bugs
Adult box elder bugs measure about 1/2 inch (12-13 mm) long. They have an elongated, somewhat flattened, oval-shaped body that is dull black or brownish-black.
Adult box elder bugs have distinct reddish-orange markings. These include a thin red line along the outer edge of each forewing. Three longitudinal red stripes are present on the pronotum, the area directly behind their head. When at rest, their wings lie flat over their bodies, often overlapping to form a characteristic “X” or “V” shape on their back.
The legs and antennae of adult box elder bugs are black, complementing their dark bodies. Their eyes are red, and the abdomen beneath their wings is bright red.
Immature Stages
The box elder bug life cycle includes an egg stage, followed by multiple nymphal stages before adulthood. Eggs are small, oval-shaped, and reddish-brown. Females lay these eggs in bark crevices on box elder trees or on the undersides of leaves during spring.
Newly hatched nymphs measure about 1/16 inch long and are initially bright red. As they grow and undergo several molts, their bodies gradually darken, and black markings appear. Early nymphal stages are wingless, but wing pads become visible as they mature through later instars, though they do not have fully developed wings like adults.
Distinguishing from Similar Insects
Box elder bugs are sometimes confused with other insects with similar red and black coloration. Stink bugs can be mistaken for box elder bugs. However, stink bugs have a broader, more shield-like body shape, and their coloration is mottled brown or greenish, lacking the distinct red “X” pattern seen on box elder bugs’ backs. Stink bugs are also slightly larger, up to three-quarters of an inch.
Kissing bugs, also known as assassin bugs, can resemble box elder bugs in color but have distinct features. Kissing bugs have a more tapered head and a distinct, needle-like proboscis, which box elder bugs lack. While both have red or orange markings, kissing bugs have less vivid patterns and feed on blood, unlike box elder bugs which feed on plant sap. Milkweed bugs also display black and orange markings, but they have a more distinct black pattern on their bodies and are found on milkweed plants.