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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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.