Eacles imperialis, the imperial moth, is a member of the family Saturniidae and subfamily Ceratocampinae. It is found mainly in the East of South America and North America, from the center of Argentina to south Canada.[1] The species was first described by Dru Drury in 1773.
The wingspan of an adult is between 80 and 175 mm (3+1⁄8 and 6+7⁄8 inches).[2] There is a high amount of variation within this species. The colors of the adult are always primarily yellow with red, brown, and purple blotches but can vary distinctly on this.[2] Light and dark morphs of this species are found in both the northern and southern regions of their range. Individuals from the northern regions of their native range may tend to have fewer dark markings.[3] Larvae can be small (approximately 10–15 mm long) and orange with black transverse bands and large spines in the first instar, to 3–5.5 inches (75–100 mm) long in the fifth instar with long hairs and shorter spines and color morphs varying between dark brown and burgundy with white spiracle patches, and green with yellow spiracle patches.[3]
Imperial moths (their many regional morphs, subspecies, and sibling species) range from Argentina to Canada and from the Rocky Mountains to the Atlantic Coast.[3] This species is the widest-ranging and northernmost in its genus Eacles.[4] Nominate Eacles imperialis imperialis has been recorded historically from New England and southern Canada, south to the Florida Keys, and as far west as Nebraska. E. i. imperialis may not appear in Massachusetts today except for a population located on Martha's Vineyard.[3] The true northern limits of the nominate's range are unknown because of possible confusion with subspecies E. i. pini in existing records. Subspecies E. i. pini occurs in coniferous and transition zone woodlands at the northern edges of the New England and Great Lakes States and northward into Canada.[2] In the southwest, it is replaced by the closely related E. oslari. Other subspecies are found in Mexico and South America. Subspecies E. i. magnifica can be found in Brazil and surrounding regions.[5]
Eacles imperialis is one of a few saturniid species in a regional decline throughout the northeastern US, with some New England states lacking records for many decades.[6] Reasons for the decline have been proposed to be the use of pesticide, insecticides, and herbicides in commercial farming, metal halide street lamps, and the introduction of parasitoids in the attempt to control the spongy moth population.[4] A population on Martha's Vineyard, Massachusetts, has been the subject of scientific and local political activity, especially concerning the preservation of the sensitive frost-bottom oak/pine habitat.[6] E. imperialis is certainly a common species of middle-Atlantic states, Appalachia, the Ohio Valley, and Deep South regions, and is associated with forest, rural and suburban habitats. It is possible that to the north, E. imperialis requires specific habitat and that the increasing fragmentation of niches such as coastal or montane pine barrens is a factor.[6]
In Florida and other southern areas, a few adults emerge in spring or early summer, but most emerge in late summer.[7] There is only one brood a year.[2]
Imperial moth larvae are polyphagous with many recorded hosts. However, there are probably regional differences in food preferences. The following plant species are the most commonly reported hosts for the imperial moth: pine species, maple species, oak species, sweetgum, and sassafras.