Cecropia Moth Caterpillars Spinning Cocoons
As a larva/caterpillar the Cecropia Moth, one of our giant silk moths, usually has five larval stages, or instars, as it matures. At the end of the fourth instar the caterpillar begins spinning a silk cocoon within which it will overwinter as a pupa. The gland which produces the silk is located below the caterpillar’s mouth.
There are three layers to the cocoon: the outer layer (stiffened and waterproofed with a liquid secreted by the caterpillar), a middle insulating layer of very soft silk strands and the innermost layer which consists of a case that encloses the pupa.
After about ten days inside the cocoon it spins in August, the caterpillar sheds its skin one last time and emerges as a pupa. For the next ten months the pupa remains encased in the cocoon as it undergoes the transformation into an adult moth. The moth will emerge next June and live only about ten days, just long enough to reproduce. (FYI, the outer layer of the cocoon was constructed within 24 hours.)
(Thanks to Jim Canfield, discoverer of spinning Cecropia caterpillar; dissected cocoon was one in which the pupa never metamorphosed into an adult)
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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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Polyphemus Moth Cocoon
Congratulations to Stein, the first person to correctly identify Monday’s Mystery Photo as the cocoon of a Polyphemus Moth!
The Polyphemus Moth is one of our giant silk moths, spinners of the largest cocoons in North America. Leaves are often woven into the surface of the cocoon in which the Polyphemus pupa spends the winter. 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.
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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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A Great Christmas Present!
If you’re looking for a present for someone that will be used year round, year after year, Naturally Curious may just fit the bill. A relative, a friend, your child’s school teacher – it’s the gift that keeps on giving to both young and old!
One reader wrote, “This is a unique book as far as I know. I have several naturalists’ books covering Vermont and the Northeast, and have seen nothing of this breadth, covered to this depth. So much interesting information about birds, amphibians, mammals, insects, plants. This would be useful to those in the mid-Atlantic, New York, and even wider geographic regions. The author gives a month-by-month look at what’s going on in the natural world, and so much of the information would simply be moved forward or back a month in other regions, but would still be relevant because of the wide overlap of species. Very readable. Couldn’t put it down. I consider myself pretty knowledgeable about the natural world, but there was much that was new to me in this book. I would have loved to have this to use as a text when I was teaching. Suitable for a wide range of ages.”
In a recent email to me a parent wrote, “Naturally Curious is our five year old’s unqualified f-a-v-o-r-I-t-e book. He spends hours regularly returning to it to study it’s vivid pictures and have us read to him about all the different creatures. It is a ‘must have’ for any family with children living in New England…or for anyone that simply shares a love of the outdoors.”
I am a firm believer in fostering a love of nature in young children – the younger the better — but I admit that when I wrote Naturally Curious, I was writing it with adults in mind. It delights me no end to know that children don’t even need a grown-up middleman to enjoy it!
Sawfly Cocoon
Sawflies are often mistaken for wasps, but there are subtle differences in appearance, including the thick “waist” of a sawfly compared to the threadlike waist of a wasp. Their common name comes from the females’ sawlike ovipositor which they use to cut into plants and lay their eggs. Certain species of sawflies overwinter as pupae inside cocoons that they attach lengthwise to twigs. These cocoons are fairly small (the pictured cocoon is just over ¼” long). Sawfly cocoons persist even after the adults emerge in the spring, as they are made of very tough material. Look for capped cocoons during late fall and winter, and empty cocoons, sometimes with the cap still attached, the rest of the year.
Hickory Tussock Moth
Most tussock moths, such as this Hickory Tussock Moth (Lophocampa caryae), are densely covered with hair-like structures called setae that bear microscopic barbs. Many people are sensitive to these setae and get an itchy rash if they handle a Hickory Tussock Moth. Even touching the cocoon of a tussock moth can cause irritation, as the setae are woven into it. Many tussock moths display warning coloration with their black, white, red, orange or yellow setae. What looks like two Hickory Tussock Moth larvae in the photograph is actually one adult caterpillar (left) and its shed skin (right). You can find these larvae feeding on hickory, walnut, ash, oak and many other trees in the woods right now. After spending the winter pupating in a cocoon in the leaf litter, a small spotted, tan moth emerges.
Spongilla Fly Cocoon
If you’ve never heard of a Spongilla Fly, you’re not alone. We don’t see its larval stage, as it lives under water, where it feeds exclusively on fresh water sponges. You can find these sponges living in the still waters of large rivers, lakes and wetlands. The beautiful silken net, as well as the small cocoon inside the net, are created by a Spongilla Fly larva after it crawls out of the water and chooses a spot on land on which to pupate (in this case on a seat cushion). The entire structure is less than ¼” in diameter.
Naturally Curious with Mary Holland 
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