On a recent walk at Mass Audubon’s Tidmarsh Sanctuary, I noticed something out of the ordinary attached to the stem of a shrub a little ways off the trail. It sort of resembled a brown dried leaf, but there was something just different enough about it that it caught my attention. Closer inspection revealed that it was a cocoon of some sort. I immediately had two conflicting thoughts: 1) I want to cut it open so I can see what’s inside (and therefore hopefully understand what this strange new thing is), and 2) I don’t want to harm whatever creature is growing inside this little structure. Luckily for my curiosity there were already multiple entry holes where something had predated the cocoon, so I felt confident that anything left inside (if there was anything left inside) was already dead. 

Free of any potential insect-harming guilt, I proceed to explore this structure in layers, “unboxing” it slowly. I first split open and pealed back the thick papery outer layer, which had been spun from coarse silk. Interestingly, the outer casing had markings from twigs and leaves imprinted into it. I then dug through the fibrous central portion. And I ultimately arriving at the core layer, the remnants of the pupal casing. Although it was now empty of its original inhabitant, it still contained the imprint of the insect’s body, incipient wings and feathery antennae. I had initially thought this might be a moth cocoon before I started digging, but the imprinted inner core verified that much for me at least.

But, which species of moth? 

Based on the sheer size of the cocoon, I figured my choices were limited to some of our largest moths, such as Luna, Polyphemous or Cecropia moths. A little digging with my field guides and online resources, and I was able to confirm that a Cecropia moth (Hyalophora cecropia) was the creator of this cocoon. Cecropia moths are North America’s largest native moth. They are a member of the family Saturniidae, the giant silk moths. These insects are so large that some females have been documented with a wingspan of up to seven inches or more. For reference, that’s about the size of a black-capped chickadee. 

What interesting discoveries have you made on your walks lately?