The Largest Moth on the Continent
Weekly Wildthings #2 - Hyalophora cecropia - cecropia silkmoth, or robin moth
When not working in our own garden, I am often to be found at the Garden at Fritz (https://gardenatfritz.com/), a nearby volunteer project which grows fresh produce for local food banks. A little over a month ago I received a WhatsApp photo from a friend working there who had seen a “caterpillar” and wanted to know what it was. From her description, I had an inkling of what it might be and walked over to get some photos.
WOW … !!
We found a group of three hatched eggs and nearby a single second instar larva of the largest moth species to be found in North America on leaves of buckthorn too. How cool is that?
First – here are the eggs – each, as you can see, neatly cracked open like boiled hens’ eggs.
The caterpillars (first instar) that would have hatched from those would have been very small and mostly black. They then will have done some skin shedding with what emerged being the lovely inch-long yellow second instar shown in this photo that I took. At this stage it was still regular caterpillar size:
Clearly three eggs hatched but only the one caterpillar was to be found – they are not exactly camouflaged so I am assuming that its siblings may have been eaten by one of the many birds around busily looking for insect food for their nestlings. Fortunately, the Garden at Fritz is used to rearing Monarch Butterfly larvae found on milkweed and so we took over the special facilities to move “Katypillar” in for safety. Food was provided.
Each larval stage (instar) should take about a week or so to progress to the next. Each time it gets bigger and the colours change. There are five larval stages (instars) in all. As each stage progresses, the caterpillar has grown in size enormously and it won’t be long now until it spins a cocoon and finally pupate. Hopefully, it will emerge as a gorgeous adult with a five to seven inch wingspan. Cocoons, in which they overwinter, are spun on the host tree or on stout grasses at their base.
Today we have this. It cannot be long now before pupation. This 5th instar caterpillar is about three inches in length … it has to be seen to be believed. You might expect this in the tropics, not in southern Quebec.
Cecropia moths have only one generation a year and they overwinter in their cocoon to emerge in the first couple of weeks of hot summer weather the next year. My friends and I will be nursemaids for a long time. As emergence draws near in the summer of 2024 guards may be posted at night.
Like other members of the giant silk moth family, the adult cecropia moth lacks functional mouth parts and a digestive system. Consequently they survive only about two weeks while seeking a mate and laying eggs. Common food plants on which they lay eggs are apple, ash, elder, cherry, lilac poplar and willow plus, as we have seen, buckthorn. Their numbers are declining as they are parasitized by the Tachnid Fly that was originally introduced to control Gypsy Moth and Japanese Beetle infestations.
But what, you ask me, will the adult look like? Here’s a picture … seven inches across
Low population density can be a problem when looking for a mate, so male Cecropia moths rely on their powerful senses to sniff out a female's pheromones. Males can actually detect females from more than a mile away and one study has suggested up to seven miles.
I am squeezing this fascinating species in as a last minute bonus article before I travel in search of more new creatures and plants. This tale is far too good not to share first though. Back again in mid August with more Weekly Wildthings.
Mid August Breaking News …
On returning from my travels I find that the caterpillar has pupated and spun its cocoon … where it will stay until next summer’s heat arrives. Wonderful news.This cocoon is big, almost three inches long.
