Adults are 3.5 to 6 mm long, oblong, olive-green colored with brown speckles, and produce a mildly offensive odor when disturbed. In the United States, characteristics of the adult kudzu bug useful in distinguishing it from other stink bugs (Pentatomoidea) include: the plate in the center of its back (the scutellum) is broader along the bottom than it is along the top, and much wider than it is long. There also appears to be a seam (pseudosuture) running lengthwise down the center of the plate. The tips of the legs furthest from the body (tarsi) are 2-segmented. The kudzu bug has a round body shape rather than the triangular to semi-elliptical body shape of other stink bugs as well as a distinctive head shape. The size of the kudzu bug ranges from a sixth to a quarter inch (3.5 to 6 mm long). Finally, the second antennal segment is shorter than that of most other stink bugs.
Adult females deposit small brownish particles on the underside of their egg mass. These unique structures are symbiont capsules which contain specific symbiotic bacteria inside. Newborn nymphs ingest content of the symbiont capsules, and the symbiont is thus transmitted from the adult females to their progeny immediately before and after birth.
Nymphs are the immature forms of the kudzu bug which hatch from the eggs. Unlike a larva, the overall body form of a nymph resembles that of an adult, but sexual maturity is not reached until it has shed its exoskeleton several times and gone through several developmental stages known as instars. Differences between instars can often be seen in altered body proportions, colors, patterns, or changes in the number of body segments.
The difference between the shields of these two different genera can prove useful for identification. Symphylus species are referred to as shield-backed bugs because the area where the wings and legs attach (thorax) is enlarged and forms a continuous shield over the abdomen and wings. This distinguishes the shield-backed bugs from most other "true bugs" (Heteroptera), but the kudzu bug has a shield as well. To distinguish between the two genera, note that the end opposite the head (posterior) of a Symphylus species is rounded, but that of the kudzu bug (Megacopta species) is cut short, or truncated.
There are two ways to distinguish the kudzu bug from Diolcus species (shield-backed bugs). The head's lateral lobes (left and right sides) of Diolcus are separated, but in species of Megacopta, these lobes are contiguous and touch along a boundary at the nose end. The second difference is the longer antennal second segment of Diolcus species.
The kudzu bug differs from other shield bugs (Plataspidae) by the following: