The Imperial Moth; Eacles imperialis, is a large night-flying moth that is easy to identify. It boasts a butter yellow color splotched with a dull purple or brown and its wingspan can reach nearly 7 inches on the females. Males are somewhat smaller, but have more patches of color. There is quite a bit of variation in individuals, so the spots on one moth won't necessarily be identical to any others you see and size can vary among individuals as well. The moth in the top image is female. The moth at the end of this article is male.
Native to North America, east of the Rockies, individuals have been recorded as far north as Canada and as far south as Mexico, although the highest population concentrates across the mid-section and southern U.S. This moth has the widest range of any of the large silk moth family.
These gorgeous moths are members of the Saturniidae family, which include the familiar Luna Moth (Actias luna) and other members of the vast giant silk moth tribe. These large moths exist only to breed and die. They have no functioning mouth parts, so live for only a few days. The adult Imperial Moths emerge after midnight and then mate the next night.
Females lay their eggs singly or in pairs on the host plants which include sweet gum (Liquidambar styraciflua) sassafras (Sassafras albidum) and several oak and maple species. Some observant watchers have noticed caterpillars feeding on Norway spruce as well, which is odd, given their other preferred foods. Caterpillars usually stick to conifer or non-conifer diets as a rule. These caterpillars go through 5 different instars (molts) before finally pupating to finish their transformation. It is interesting to note that the caterpillars that feed on the deciduous trees are brown in color, while those with a diet of conifers are green. These caterpillars are solitary feeders and are rarely present in significant numbers, so pose no threat to the foliage of your garden plants. They have a fierce appearance with horns and spines, but possess no stinger or toxic venom.
The mature caterpillars drop to the ground and start searching for soft soil or mulch suitable for burrowing. They dig into the soil and pupate for the winter, emerging in the spring as adults, ready to carry on the cycle once again.