You probably don’t think much about the fuzzy critters crawling through your garden until you see a leaf gone. And then when you do notice one, you panic: Is it destroying my roses? Do I have to run out for spray right this second? The answer is almost always no. Even though they may appear to be trouble, most of those larvae are actualy beneficial and harmless.
There are hundreds of these creature here in Ontario, and knowing which ones live in your yard will change the way you view your yard. It shifts the mindset from pest control to ecosystem management. To help us identify some of our most common species in the province, here’s a breakdown of the key identifiers by species (the visual guide is above).
How to Tell Caterpillars Apart
The first clue: body markings. Does it have stripes? Spots? Bands across or running along segments of its body? That will help narrow things down fast. But wait! It doesn’t stop there. There’s also hair type. If it has smooth body, that’s one set of families; if spiny or tufted, then other sets. Sometimes this texture detail can tell a harmless butterfly larval form from a potentially irritating moth species whose contact may cause rashes on your own skin. So knowing how to tell them apart is a saving grace; and no need for rash words…or rash bumps later.
Take the Luna Moth caterpillar for instance. They are bright apple green with little red-orange knobs down each side. They are the larvae of one of our largest and loveliest moths in Ontario. It eats birch trees and maples. So if you see these guys, know that your local woods is sufficiently healthy to sustain this kind of life cycle.
At the other end of the color scale is the Banded Woolly Bear. You probably remember this guy or gal from all those old stories as a kid about how its pattern can predict harshness of coming winters. It is black at either end with a rustier-orange center band. Edges are the name of its game… Not cultivated flower beds, but more weedy things such as grasses and plantain. Knowing this will tell you both what to leave well-enough alone and also where to expect them to be.
Another huge tipoff is their host plants. The chart shows some common combinations. For instance, the Monarch is on milkweed, while the Black Swallowtail is on parsley and other carrot family plants including dill. Is there a yellow-green caterpillar with black bands and yellow dots? If that is the case, there is a good chance it is on your dill plant.
Why this host specificity… Why does it matter so much to plant natives, when you’re thinking about trees, especially? One oak tree alone may be home to dozens of species, such as the Cecropia Moth, which has bumpy red, yellow, and blue spots in rows across its body. And that visual detail tells us the tree is a complex habitat below the bark, where things thrive.
And then there are some caterpillars you’ll want to admire from afar: The Io Moth, for example, whose branched stinging spines will itch your skin. Or the White-marked Tussock Moth, which has red markings and striking white tufts but also bears irritating hairs. Not all fuzz is friendly; these remind us that not all caterpillars are harmless.
And many defoliating species, like the Spongy Moth, are actualy forest ones (though thankfully most don’t kill trees except when their numbers explode). Knowing what’s normal helps avoid overreacting, and yes, a few chewed leaves are the price we pay for a food web that feeds our songbirds.
With a little guidance, raising caterpillars can be simpler than you imagine. Feed them cuttings of their proper host plant in a well-ventilated enclosure and keep everything clean. Then, at emergence time, set the adult butterflies or moths free right back where the larval form originated. That’s good for regional biodiversity (and conservation of each place’s gene pool). And it ties your observations to the particular habitat that the creature depends on.
The next time you see A CRAWLER, reach for your camera first then respond. What’s it eating? What pattern does it match? Compare those markings to your reference photos and observe which plant it has in its sights. Maybe you are witnessing the future of your garden, a pollinator in training that is learning to fly. And that little delay could of turned into something useful, turning an annoyance into a moment of discovery.