Summer of the Silkmoth

There are few caterpillars more exiting to find than the giant silkmoths.  Their enormous size, unique appearance, and amazing life history make them fascinating creatures to study and observe.  Their numbers can fluctuate from year-to-year, and 2013 has been incredible for silkmoths.  Last week’s discovery of two Cecropia Moth caterpillars in the apple tree in the backyard at NBNC was definitely a highlight.

Cecropia Moth caterpillar as it was found!

 The Cecropia is probably Vermont’s largest moth, and the mature caterpillars are as long and wide as an index finger.  They have an electric-lime body, covered in colorful, spiky protuberances of orange, yellow, and blue.  Despite their vivid appearance, they can blend quite well into a leafy canopy.  There are, however, countless other creatures searching for these caterpillars with the intent to cause them harm.

The two giant caterpillars feed in the apple tree

Close-up of fly eggs

When we think of caterpillar predators, we often picture birds carrying a beak-full of caterpillars to hungry nestlings.  It is other insects, however, which pose a much more substantial threat to caterpillars.  The Cecropias we found at NBNC were both host to dozens of tachinid fly eggs (the small, white ovals on the caterpillar’s back).  The fly larvae will ultimately kill and consume their caterpillar hosts.  

We caught this tachinid fly
laying eggs on the Cecropias

The threat of six-legged predators has been compounded by the introduction of a fly, Compsilura concinnata, to the northeast in order to control the invasive gypsy moth.  This introduced fly has developed a taste for more than just gypsy moths, and is thought to be playing a role in the decline of the Cecropia and other giant silkmoths.  Whatever the reason, silkmoths numbers have been dropping for decades and the effects of this decline on other species are just beginning to be understood.

While the adult giant silkmoths won’t fly again until next spring, look for their giant caterpillars this summer and fall and share with us what you find!

This Luna Moth caterpillar was also found last week at NBNC