Last summer, in addition to the 120 luna moth caterpillars I reared, I also raised a dozen cecropia ‘pillars. I’ve never seen a live adult cecropia, but when I was little my mom’s stories about the one she saw as a young girl captivated me. These are the largest of the giant silk moths found in North America and are native to the eastern half of the United States. Six of my cecropia caterpillars survived to spin some very large cocoons (that’s a great survival rate for indoor rearing – they’re a tough species to raise), and the hatching season is now upon us!

Adult cecropia - photo by Bill Oehlke
Like luna moths, cecropias in the New England states spend their winter in their cocoons, so my cocoons have been resting in the fridge since last November. I just brought them out on May 14 and they’re now in my terrarium. I don’t have an exact count on expected hatcing times, but I believe it’s 30-35 days for cecropias, once they come out of the cold. Lunas are typically 14-18 days, but last spring was cool and my lunas all hatched in 19-21 days. I’m anxious to see these big guys eclose (the scientific word for hatching), but some of my luna caterpillars last August spun cocoons and then died in them. So I can’t assume the cercropias are still viable. So I conducted an experiment to see!
Unlike a luna cocoon, which is little more than a leafy wrapper, the cecropia spins two dense layers of silk – an inner and an outer cocoon. Within the inner cocoon, the caterpialler metamorphs into a pupae (the moth’s equivalent of a butterfly’s chrysalis.) It’s within the hard pupae case the caterpillar metamorphs into the adult moth. It’s possilble to remove the pupae from the cocoon, but you must be careful there’s adequate humidity for a bare pupae case. Since mine were in my terrarium, I wasn’t worried, so I cut one of the cocoons open two days ago to take a peek!
Here’s a cocoon as the caterpillar spun it. Nearby leaves get incorporated into the cocoon, but their’ not really structural as they are with the luna. The leaves are more “nice to have” than a “need to have.”

Cocoon as spun by cecropia caterpillar
I peeled away the leaves and the underlying silk cocoon was still very tough and durable. In this next photo you can see that I’ve already snipped through the outer silk cocoon (along the right edge). That’s the easy part.

Cecropia cocoon with leaves stripped away
By carefully separating the cut edges of the outer cocoon, you can see the inner silk cocoon within.

Exposed inner silk cocoon of Hyalophora cecropia
The inner cocoon was much denser, and here I had to be much more careful. You don’t want to disturb or puncture the pupae case within, and it’s very close to the interior surface of that inner cocoon. It took a lot of patient snipping to actually get through the tough, dense silk.

Initial cut on the inner silk cocoon...so far, so good!
I cut the length of the inner cocoon and held my breath as I opened the slit. If the pupae was dead it would be nearly black. A healthy pupae would be a darkish orange-brown. And here’s what I saw…

- A healthy cecropia pupae within her cocoon!
She looked great! The other reason to open a cocoon is that it’s the only way to sex whether the moth is male or female. We’re looking at the front of the head of the pupae. The horizontal segments lower down (and partially covered by the cocoon) are her abdominal segments. The darker portion that seems to wrap around her shoulders like a shawl are her wings. They’ll be very scrunched up when she ecloses, so her first order of business will be to pump up her wings quickly before they harden.
The feathery structure that drapes down over her face are her antennae, and that’s how I know she’s a she. As large as they are, a male’s would be twice as wide. The males use their antennae like our “nose” to “smell” the pheromones the female pumps into the air like a perfume. She won’t fly until after she mates. He’ll fly in search of her, which is why his antennae are so much more developed.
So today is day 10 in the cecropia watch – stay tuned, moth fans!