Finding giant silkworm caterpillars (family Saturniidae) or observing the resulting giant moths was once a common occurrence. Notable members of this moth family include Cecropia (Hyalophora Cecropia); Luna (Actias luna); Polyphemus (Antheraea polyphemus); Promethia (Callosamia promethean); and the impressively named Hickory Horned Devil (Citheronia regalis).
However, people started noticing a decline in the numbers of these unique insects over the past few decades. Anecdotal observations were eventually supported with scientific data and a number of theories were proposed ranging from insecticide exposure to unintended consequences brought about by introducing non-native beneficial insects.
For example, from 1906 to 1986, the generalist parasitoid fly, Compsilura concinnata (family Tachinidae) was repeatedly introduced from Europe to North America as a biological control agent against 13 pest species. Gypsy moth caterpillars (Lymantria dispar) were a favored target. However, research conducted by a University of Massachusetts group in 2000 showed this tachinid fly was capable of producing an 81% mortality rate for Cecropia moth caterpillars.
Whatever the reason for the decline, some of these moths seem to be experiencing a reversal of fortune in recent years. I recently came across Cecropia moth caterpillars in two different locations in southwest Ohio. The first time, I actually didn't know that I was seeing because first and second instar caterpillars look nothing like the later instars most commonly depicted in printed and online resources. The caterpillars I saw on Sunday had reached the 3rd instar stage which meant they clearly had the attributes most often associated with the larvae of the species.
While giant silkworm moths may be crawling their way back, they still need our help. Specifically, we should keep the caterpillars alive through educating the public. Despite their impressively large sizes (4 - 5" long), the caterpillars cause little damage to plants. Most are solitary feeders and are not considered serious plant pests. They should never be targeted by an insecticidal application. The caterpillars become some of our most impressive moths, adding beauty to our forests and landscapes.