Invertebrates
Imperial Moth
Eacles imperialis · also called imperial moths
Drawn to a porch light on a warm summer night, an imperial moth spreads broad yellow wings marked with irregular patches of purple-brown, one of the largest moths in North America and a species whose caterpillar can look so different from one individual to the next that even the same clutch of eggs can produce what look like several different species.
Overview
The imperial moth, Eacles imperialis, is a large, boldly patterned moth native to forested habitat across a broad range of eastern North America, from southern New England south to Florida and west to the Great Plains. Its impressive size, dramatically variable caterpillar colouration, and complete lack of feeding as an adult make it one of the more visually striking and biologically distinctive giant silk moths in North America.
A caterpillar with more looks than colours have names
Few insects illustrate individual variation as dramatically as the imperial moth caterpillar, whose colour can range from green to brown to nearly black even among siblings from the exact same clutch of eggs.
Status
Least Concern overall, though populations in parts of the northeastern United States have declined significantly or disappeared, linked to artificial lighting, pesticide use, and introduced parasitic flies.
Imperial Moth: common questions
Why do imperial moth caterpillars look so different from each other?
This species' caterpillar shows remarkable colour variation, appearing in shades ranging from green to brown to nearly black, with different-coloured individuals sometimes occurring within the very same clutch of eggs, a variability that can make it genuinely difficult to recognise multiple caterpillars as the same species without prior knowledge.
Why doesn't the adult imperial moth eat?
Like several other members of its family, the adult imperial moth has no functional feeding mouthparts and does not eat at all, instead living for only a short period on energy reserves stored up during its much longer caterpillar stage, with its brief adult life focused entirely on finding a mate and reproducing.
Why has the imperial moth declined in parts of the northeastern United States?
Populations in parts of the Northeast have declined significantly or disappeared entirely, a trend linked to factors including artificial nighttime lighting disrupting adult behaviour, pesticide use, and parasitic flies originally introduced to control invasive gypsy moth caterpillars that also attack the caterpillars of native moth species such as the imperial moth.
How can you identify an imperial moth?
Look for broad yellow wings marked with variable patches and speckling of purple-brown, a large overall size among the biggest moths found in North America, and a caterpillar stage so colour-variable that it can be more useful to look at the adult moth's fairly consistent wing pattern for a confident identification.