While adult stink bugs have a shield-like appearance in terms of shape, young stink bugs have a quite different appearance. Baby/young stink bugs, called nymphs, go through five instars before reaching adulthood. Along the way, nymphs appear drastically different than their adult counterparts. Eggs typically hatch after three to five days, with each instar taking about a week before culminating with the final molt to become an adult. Young stink bugs generally feed on the host plant from which they hatch, until moving on to find new food sources nearby.
The United States is home to two main species of stink bug: the brown marmorated stink bug, Halyomorpha halys, and the green stink bug, Acrosternum hilare. Young brown marmorated stink bugs tend to appear dark around the head with a red/orange and black striped body with black stripes. As the insect progresses through its nymphal instars, the body turns rust-red with black spots. The shape resembles a tick, as the bug appears more oval and also has red eyes. The nymphs of the green stink bug appear more oval in shape and are predominantly black in color before becoming more yellow, red, and then green as each molt moves the insect closer to adulthood. Neither species is capable of flight during nymphal development.