by Sarah Treanor Bois, Director of Research & Education for the Linda Loring Nature Foundation
According to Butterflies and Moths of North America (butterfliesandmoths.org) there are 172 species of moths and butterflies that have been documented from Nantucket County. As such, that means there are that many caterpillars out and about growing, feeding, and getting ready to pupate. Most school children know about the life cycle of the monarch, how the caterpillars feed exclusively on milkweed and then turn themselves into a chrysalis. The metamorphosis is magnificent with the familiar monarch butterfly emerging after about 14 days.
While butterflies usually get all the attention, I’d like to focus in on the beauty and wonder of the island’s caterpillars. Caterpillars often get a bad rap especially with many gardeners and homeowners who worry about their ornamental plants. Many caterpillars are only noticed by the public when they come in large numbers; think Eastern Tent Caterpillars in a “boom” year. However, the diversity and uniqueness of many of these caterpillars surpasses some of their drab adult counterparts. Here we will highlight a few that may be seen this time of year.
Cecropia Moth caterpillar (Hyalophora cecropia). The first instar of this species is tiny, black, generally reared on cherry. However, it’s the later form of the caterpillar that really is a show. When the caterpillars mature in autumn, they are a blue-green color and about 4 inches long. Along their body are lines of bulbous structures each with small clusters of black guard hairs. These bulbous structures are red, blue, and yellow, creating a circus creature feel. These larvae feed upon many common trees and shrubs, including maple, birch, and apple. The adult moth really is quite beautiful and is the largest moth in North America.
Another striking caterpillar is seen in the Io moth (Automeris io). These bright green caterpillars have two stripes down their sides, a red one on top and a white stripe just below. These caterpillars are covered in branched spines. These spines do sting with the intensity of a stinging nettle plant, though the sting can last for hours. The Io moth itself is quite remarkable with two large eye-spots on the hindwing.
Spiny Oakworm (Anisota stigma) is most visible when the caterpillar is fully grown. At this stage, the head is orange and the body is reddishbrown. There are characteristic black spines on the thorax (the upper segment of the body) which are long and prominent. A series of shorter, black spines occur along the back and sides of the body. As its name implies, the Spiny Oakworm feeds primarily on oaks. On Nantucket, it likes the scrub oaks as well as the more traditional black and white oak trees. Spiny Oakworm populations have declined across much of the northeast in recent years, but they seem to be doing well on Cape Cod and the Islands.
The caterpillar of the Hickory Tussock moth (Lophocampa caryae) is completely covered in long, white, hair-like setae arranged in spreading tufts. Additional tufts of black with some longer hair clusters give this caterpillar a rock star appearance. These hairs cause itchy rashes in many people, particularly those prone to allergies, and may resemble exposure to urushiol, the chemical cause for poison ivy rash. Despite its name, Hickory Tussock moths feed on nut trees, but aren’t too picky. They are visible now on Nantucket, but will soon be tucked away in webs to pupate on their way to emerging as moths next spring.
This next caterpillar can be seen right now in its first instar stage. The puss or flannel moth, (Megalopyge crispata) looks cute and fuzzy, but DO NOT TOUCH! This little one has the distinction of being one of the most toxic caterpillars in North America. Closely resembling the cute backside of a rabbit, under the soft, white fuzz, this deadly creature has hollow poison-filled stinging spines that can act like tiny poison darts. While they won’t kill you, they pack a punch. I myself had to go to the emergency room when I accidentally squashed one into the palm of my hand. The swelling moving up my arm was concerning, but nothing that a few Benadryl couldn’t handle. So, look, but don’t touch this dangerous beauty.
Nantucket is known for its globally rare sandplain grasslands and coastal heathland habitats. These systems make, Nantucket host to some rare and state-listed Lepidoptera (moths and butterflies) in addition to the species already mentioned. From his survey work in the early 2000s, lepidopterist Mark Mellow (with the Lloyd Center for the Environment) documented 19 statelisted rare moths on the island. These include the scrub oak-loving Barren’s Buckmoth (Hemileuca maia) and the yellow inchworm of the Chain Dot Geometer (Cingilia catenaria), a sandplain grassland specialist. Further, of the 39 species listed by Massachusetts Natural Heritage and Endangered Species program, 44% are restricted to native heathland or shrubland (including scrub oak barrens) habitat. Further reason to continue protecting Nantucket’s unique habitats.
If you’d like to know more about the caterpillars, their favorite host plants, and what time of year to expect them, check out Caterpillars of Eastern North America: A Guide to Identification and Natural History by David Wagner. This field guide has beautiful photographs and categorizes around 700 species. My favorite part is that you can also look caterpillars up by host plant to narrow the search.