The brown marmorated stink bug is a species not seen in the United States before 1998. It was introduced into Pennsylvania at some point in the mid-1990s and has spread into many parts of the United States. Adults are about 1/2 to 5/8 inch long and shield shaped. They have a marbled brown color with patches of white, especially on the antennae and sides of the body. Young brown marmorated stink bugs are variable in size up to 1/2 inch, dark brown with red, orange, or yellow banding, and with white bands on all the legs. The young also have distinct red eyes.

Females lay barrel-shaped eggs in clusters of 20 to 30 on undersides of leaves of a variety of plants. There are 5 instars (immature stages). They range in size from the first instar at 3/32 in to the fifth instar, which is 15/32 in length. The eyes are a deep red. The abdomen is a yellowish red in the first instar and progresses to off-white with reddish spots in the fifth instar. The legs, head, and thorax are black. This species probably has a single generation per year in Pennsylvania depending on the temperatures. Warm spring and summer conditions could permit the development of 2 or 3 generations. However, in parts of subtropical China, records indicate from 4 to possibly 6 generations per year. Adults will emerge sometime in the spring of the year (late April to mid-May), and mate and deposit eggs from May through August. The eggs hatch into small black and red nymphs that go through 5 molts. Adults begin to search for overwintering sites starting in September through the first half of October.

Although brown marmorated stink bugs are a nuisance pest indoors and outside, they are also a significant agricultural pest in many different crops. They are attracted to structures for the purpose of overwintering. In late summer, brown marmorated stink bugs will congregate on shrubs and trees near structures, especially those plants with berries or fruits. They move indoors through gaps and openings under siding and along conduits. Indoors, they will become active during winter on warmer, sunny days and toward the end of winter as they emerge in spring. These insects are not known to cause harm to humans, although homeowners become alarmed when the bugs enter their homes and noisily fly about. Stink bugs will not reproduce inside structures or cause damage. If many of them are squashed or pulled into a vacuum cleaner, their smell can be strong and unpleasant.