Promethea Moths Pupating
Now is a perfect time to look for cocoons, with leaves off deciduous shrubs and trees. Giant silk moth cocoons are especially evident, due to their large size (often 2″-4″). The Promethea Moth caterpillar (Callosamia promethea), one of several giant silk moths in the Northeast, hatches in the summer and reaches its full size by fall. It then chooses a leaf and reinforces the leaf’s stem, or petiole, with silk so as to make it less likely that the leaf will detach from the branch it is growing on. The caterpillar then spins its silken cocoon inside the curled leaf, and spends the winter pupating inside the cocoon. Look for their well-camouflaged cocoons on low-hanging branches.
Come May or June, the moth will emerge, and if it’s a female, will produce pheromones that may attract males from as far as several miles away.
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Cecropia Moths Mating
Cecropia moths (Hyalophora cecropia) are the largest native North American moths. They are members of a group of moths known as giant silk moths (family Saturniidae), renowned for their large size and showy appearance.
Having overwintered as pupae inside silk cocoons they spun (as larvae) in the fall, the adults emerge at this time of year often during the first spell of hot, humid weather by dissolving one end of their cocoon with their saliva. The female Cecropia emits pheromones at night that are so strong that males can detect them with their feathery antennae from as far as a mile away. Once paired, Cecropia moths proceed to mate for a full day before parting company.
Shortly thereafter the female moth lays up to 100 eggs, often on both sides of a leaf. Due to a lack of functional mouth parts and no digestive system, the adults seldom live more than two weeks after mating. (Photo: female Cecropia moth on left (larger abdomen filled with eggs; narrow antennae); male on right (smaller abdomen; broader, more feathery antennae). Many thanks to Lorraine Vorse for photo opportunity!
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Luna Moth Caterpillars
The large, green swallow-tailed moth known as the Luna Moth (Actias luna) is familiar to many. Its short life of about a week begins in June when it emerges from its cocoon, mates, lays eggs and then dies. The larval stage of this giant silk moth is not as well known, but has just as striking an appearance as the adult moth. It is an unforgettable lime-green with tiny magenta spots along its length.
When threatened by a predator, Luna Moth caterpillars have several defensive behaviors, including emitting clicks as a warning and regurgitating the contents of their intestine, both of which have proved to be effective deterrents. Look for these caterpillars on their host trees which include birch, hickory and walnut. (Thanks to Susan and Dean Greenberg for photo op.)
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Promethea Moth Cocoons
At this time of year, most deciduous trees have lost their leaves. Bare branches make looking for cocoons and finding them much easier. A single leaf dangling from an otherwise barren branch of a tree might very well turn out to be the winter domicile of a Promethea Moth (Callosamia promethea) pupa.
These giant silk moths construct their protective two-inch-long silken cocoons while still in their larval/caterpillar stage. First silk is spun around the stem of the leaf (petiole) as well as where the petiole attaches to the branch, in order to reinforce the attachment of the leaf to the tree. The cocoon is then spun, with the leaf serving as its outer covering. The result is a perfectly disguised shelter that looks like a dead leaf hanging from a branch.
The caterpillar pupates after completing the cocoon. After spending the winter in the pupal stage, the adult moth will emerge in early summer through a valve-like opening at the upper end of the cocoon.
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Polyphemus Moth Cocoons
The Polyphemus Moth is a giant silk moth, a member of the Saturniidae family which includes some of the largest species of moths. Giant silk moths derive their name from both their size as well as the fine silk they use to spin the cocoons which serve as protection for the pupal stage in their life cycle.
Most Polyphemus Moth cocoons start out attached to a tree branch, although some are spun among leaves or grasses on the ground (see pictured cocoon). They are oval, roughly 1 ½” long and nearly an inch wide. Cocoons in trees are susceptible to attack by squirrels and woodpeckers, whereas mice are the biggest threat to cocoons on the ground.
The moth overwinters as a pupa inside the cocoon. Unlike most other giant silk moths’ cocoons, the Polyphemus Moth cocoon lacks an escape “valve” at one end. In order to emerge (as an adult) from the cocoon the summer after it spins it, the moth secretes an enzyme that digests and softens the silk at one end. Then it moves about the cocoon in a circular pattern, tearing the softened silk with two spurs located at the base of each wing on its abdomen. Eventually it escapes by splitting the silk and pushing the top up.
Luna Moths Emerging
June is giant silk moth month, when these giant-bodied/winged moths in the family Saturniidae emerge. Perhaps the most familiar giant silk moth is the Luna Moth, Actias luna. One of the largest moths in North America, its wingspan measures 4 ½ inches. If you see one of these beautiful creatures, you are witness to its very short adult lifespan. After emerging from their cocoons, Luna Moths live for only about a week, during which time their sole mission is to mate. Like many other ephemeral insects, adult Luna Moths have no mouthparts and thus, do not eat.
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Promethea Pupae Parasitized
Although a lack of snow makes tracks difficult to find, there are other, more permanent, animal signs such as bird nests and cocoons that are visible this time of year. Among the more obvious is the cocoon of the Promethea Moth – a giant silk moth. When the time for pupating arrives the Promethea caterpillar selects a leaf and strengthens its attachment to the tree by spinning silk around the petiole of the leaf as well as the branch it grows on (to assure that it doesn’t fall off the tree). With more silk it rolls the leaf up into a tube and then proceeds to spin its cocoon inside the rolled-up leaf, leaving a valve-like structure at the top of the cocoon through which the adult moth exits in the spring.
Unfortunately for silk moths, many are parasitized by flies and wasps (there are nearly 100 natural parasites that affect the 24 species of silk moths east of the Mississippi River). Frequently flies or wasps lay their eggs in silk moth caterpillars and then develop inside them. Eventually the fly or wasp larva secretes a substance that causes the caterpillar to pupate, at which time the fly or wasp also pupates and then exits the moth pupa and cocoon (see exit hole in smaller photo), causing the death of the moth pupa. Silk moth populations are decreasing, in part as a result of these parasitoids. Among others, a non-native parasitic tachinid fly, Compsilura concinnata, is wreaking havoc on silk moths.
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Rosy Maple Moths Emerging
This is the time of year when moths rule the nights. Many moths in the silkmoth family, Saturniidae, emerge in June, including giant silkmoths such as Luna Moths and Cecropia Moths. A smaller member of this family also appears at this time of year. While the 1 to 2-inch Rosy Maple Moth (Dryocampa rubicunda) wingspan doesn’t come close to many of the giant silkmoths’ 5 to 6-inch wingspan, its pink and white or yellow coloring is stunning. Adults emerge mid-May through mid-July in the late afternoon, and they mate in the late evening. Females begin laying eggs at dusk the next day in groups of 10-30 on leaves of the host plants (Red, Sugar and Silver Maples, as well as Box-elder and some oak trees). The eggs hatch in about 2 weeks and the larvae are referred to as Green-striped Mapleworms. They occasionally do considerable damage to their host trees when their population soars. In New England there is only one brood per summer, with the larvae pupating and overwintering underground.
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Promethea Moth Cocoon
When a Promethea Moth caterpillar, one of our giant silk moths, is ready to pupate at the end of the summer, it strengthens the stem, or petiole, of a leaf on its host plant with silk and then attaches the silk to a nearby branch, assuring that the leaf will remain attached to the tree. (Imagine having the instinctive foresight in your youth that this caterpillar had!) The caterpillar then curls the leaf around itself and spins its cocoon inside the curled leaf. The cocoon dangles from the host plant throughout the winter and in early summer the moth emerges. Now is the perfect time for finding a Promethea Moth cocoon, as last year’s leaves are gone on most trees, and this year’s buds have yet to open. Look for a tree or shrub that has just one dead leaf hanging from one of its branches. (Cecropia caterpillars favor black cherry, poplar, ash, maple, oak and willows trees among others.)
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