Welcome back to Ask a Naturalist: your own personal “Google” for information on all things natural on PEI. I’ve been getting lots of questions about the many caterpillars appearing in yards, gardens, hedges, and trees around the Island these days so let’s take a look!
It’s unfortunate that caterpillars’ leaf-eating lifestyle gives them such a bad reputation. Prime examples are the Fall Webworms appearing across PEI right now: countless tree limbs will be needlessly amputated in efforts to control these harmless caterpillars (you can read more about them here: https://www.pei-untamed.com/post/fall-webworms). While there are caterpillars that can be problems – Spruce Budworm and Spongy (formerly Gypsy) Moth are two of the most notorious – we have hundreds of species on the Island. A few non-native species can cause economic damage to agricultural crops, but the vast majority cause no environmental damage and some are important pollinators as adults.
Most of our moths overwinter as larvae (caterpillars) or pupae (cocoons), which is why we see more of them this time of year. They’re feeding up and seeking out cozy accommodations to get through the winter and will re-emerge in spring to develop into adult moths. Caterpillars come in all shapes, sizes, and colours, and the appearance of any one species can change as it grows through several stages called instars.
The American Dagger Moth caterpillar (Photo 1) is bright yellow in its earlier stages, fading to pale before it pupates. Those black hairs are present at all stages and help with identification. The hairs of this common native caterpillar can cause skin irritation if touched and so it's best not to handle it. These caterpillars feed on a range of hardwood trees and shrubs and tend to attract attention in urban and suburban areas thanks to their bright colour, but they don’t cause any damage (despite click-bait headlines exaggerating their ‘sting’).
The White-marked Tussock Moth Caterpillar is another fuzzy species that can cause skin irritation for some people (Photo 2 by Beth Hoar, used with permission). Unlike the others shown here, this native species overwinters as eggs. These caterpillars will soon begin creating cocoons and in September adult grey-white moths will emerge to mate and lay eggs. We have five species of Tussock Moths on PEI, and while their caterpillars come in a range of different colours, all have those characteristic tufts on their backs.
Not all caterpillars are fuzzy, as the Common Gluphisia Moth shows (Photo 3). This common native caterpillar feeds on Poplar and Willow, but adult moths don’t feed at all – like most of the species shown here, they live just long enough to mate and lay eggs. This is among the most widespread caterpillars in North America and has been reported from every US State and Canadian Province, although not yet from the Territories.
Our largest species is the Cecropia Moth, and its caterpillar looks like something from a cartoon: a huge bright green body with various red, orange, and blue knobs (Photo 4 by Beth Hoar, used with permission). These native caterpillars will feed on virtually all our hardwood trees and shrubs but don’t do any long-term damage. The moths themselves are beautiful and a treat to see in June and July, but don’t feed and only live for a week or two.
Some of our oddest-looking caterpillars are the hornworms, including the Bedstraw Hawkmoth (Photo 5). Named for the conspicuous horn at their hind end, this group tends to raise the ire of gardeners thanks to the Tomato Hornworm (the caterpillar of the Five-spotted Hawkmoth) which can be a pest. But Bedstraw Hawkmoth caterpillars feed on Bedstraw, Fireweed, and Evening Primrose and don’t cause problems for gardens or agricultural crops. Of the species shown here, this is the only one that matures into an adult moth that feeds; you may spot Bedstraw Hawkmoths on garden flowers and shrubs including Lilac.
Size, colour, markings, and the presence of hairs, horns, knobs, or spikes can all help you identify your caterpillar or at least narrow it down to group. BugGuide.net is an excellent online resource to help.
If you have a question about PEI’s wild side, it’s likely others do too! So, follow me here or on Facebook, join the conversation, and Ask a Naturalist about PEI untamed!
Comments