As their common family name indicates, giant silk moths are fairly large in size with the Cecropia and Glover’s moths in Colorado having wingspans of nearly 5 ½ inches. These two species are very similar and yet have distinct variations that separate the two. The first variation is their location. For the Cecropia moth, their habitat is lower elevations of the foothills and Front Range of the eastern portion of Colorado extending to the eastern portion of the Unites States; whereas the Glover’s moth is commonly found at higher elevations and west of the Continental Divide. Cecropia moths tend to have gray areas of color along the interior of the wings versus the red/brown of the Glover’s moth. As caterpillars, distinguishing features are a bit more limited and are only related to the coloring of the tubercles along their backs. Glover’s moth caterpillars are distinctively yellow where as Cecropia moth caterpillars are a bit more colorful with blue, yellow and red being common. Both caterpillars are large at 3 to 4 inches when full grown and bright green in color. In both species, the adult male moths have large antennae that resemble a fern leaf or plume.
The lifecycle of these moths is fairly simple. Adults emerge from their cocoons from April to June, living for only about a week, just long enough to reproduce. They do not feed in the adult stage and are commonly seen around lights in the evenings. Eggs are laid in small clusters on various trees or shrubs which depending on the moth species and will become host to the hatching caterpillars. Glover’s are commonly found on maple, willow, chokecherry, alder and a few other plant species; where as the Cecropia caterpillars will feed on lilac, walnut, willows, apple, ash and poplar among other species. Initial feeding by the caterpillars may be done in groups which later disburse into singular feeding sites. Eventually the caterpillars wander off in search of a sheltered area at the interior of a plant or shrub in which they can create their heavily woven silk cocoon in which they will over-winter as a pupa. Decreasing numbers of giant silk moths have been noted in recent years and may be due to the mortality of adults around lights and the introduction of parasitizing species of tachinid flies.