Sue Silva has a lifetime of experience with bugs. In some ways, she is a bug whisperer, as insects seem to flock to her side and her greenhouse, and she is often sharing with me the more interesting and unique ones that cross her path. As a farmer, gardener and outdoor person, she has seen many species of insects in her days. So when Sue came across a hornworm caterpillar that was new to her, my curiosity — and hers — was piqued.
A review of my insect library and a web search did not yield a positive identification of the sizeable bright green caterpillar with very distinctive body markings and large black horn. Surely it was a hornworm, but none of the local species was a match. The next step was to cast a wider net of expertise. However, the identification that the experts came up with didn’t seem to be a true match.
Enter Judy Holland McChesney, artist, gardener and butterfly aficionado. She is not one to let mysteries mire so; lickety split, she found a perfect caterpillar match. Our mystery caterpillar is none other than Agrius cingulata, also known as the sweet potato hornworm.
With that ID, those experts got excited.
Agrius cingulata, or the pink-spotted hawkmoth, is a species that is not often seen in its caterpillar form in New England. As an adult it is generally a fall migrant or stray to our region, and it is the moth that is seen, but rarely the caterpillar. Thus we now have a breeding record! But it gets better. The reason this caterpillar was so difficult to identify is that it is not the usual color pattern for the sweet potato hornworm, but a more unusual morph. The major literature sources for the species mention that the caterpillars may be green, brown or a combination of the two, but most published images are of dark brown to nearly-black forms. Sue’s specimen was bright green, so its photograph makes a very useful addition to the Lepidoptera literature. In fact, the photo of Sue’s caterpillar will likely be included in a soon-to-be-published book of western North American caterpillars.
The sweet potato hornworm caterpillar is widespread in the southern and western parts of the country. It’s common in Texas, California and even Hawaii, where this species is a pest to crops much like its local reviled relative here, the tomato hornworm. Both can eat voraciously day and night and do some serious damage to food crops. Sue’s new Massachusetts sighting, however, was not the only freaky fall caterpillar observed in the commonwealth. Another sweet potato hornworm was identified and photographed in Barnstable in late October.
What draws this southern belle to our cold climes this late in the season? Is it due to last year’s warm winter, climate change or is it just an anomaly? All good questions for which no simple answer applies. If you have been reading the column next door, you will also know that there have been some interesting and unusual bird sightings of late.
The fate of this individual caterpillar is unknown. It is certainly a long way from its home, and now it is also a long way from Sue’s home. However, in its wake it leaves behind a considerable amount of admiration and wonder, and even a modicum of celebrity, for its unusual ability to survive a New England November. Celebrities on this Island come and go, but this little one deserves a little extra fame, for no one is sure exactly how it came or where it went.
Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown.