Consequently, there is strong incentive for scouting for this pest. The degree of infestation is highly variable among orchards. A Connecticut study showed STLM to infest apple and wild crab apples. A broader host list is sometimes given, but this may arise from confusion between STLM and closely related species.
Females are a little larger than males.
The larva passes through five instars. During the last two instars, the body is more cylindrical and the head is more oval, a typical caterpillar head capsule. There are now more apparent legs and prolegs. For much of its development, the larva is white to pale green. During the final instar, color changes to a pale to deep yellow.