A brown caterpillar crawls across the oak leaf in your yard. Before it gobble up your shrubs, you’d like to reach for garden shears to snip it away. Hold on a tick: First, learn if the thing is harmless. Or will make you wish you hadn’t touched it. Often it’s a matter of little-known details; here’s what to look for, so your hands won’t hurt; and neither will your trees, thanks to any no-longer-needed chemical mixes.
That’s how it’s laid out in the visual guide (above), which covers 12 familiar garden- and forest-dwelling species across North America: their patterning, and what kind of plant they feed on. Because the color brown works so well as camouflage in wooded areas, you might think all brown caterpillars are the same type of insect. But not at all. The bugs evolved to blend with whatever surrounds them; twigs or dead leaves or the bark itself, to avoid being detected by predators.
How to Identify Brown Caterpillars Safely
Six key tricks appear on the chart. Some have slender bodies that mimic twigs, and others has rough skin that mimics tree bark. Learning these patterns will speed your searches. What you’re looking for is a break in leaf litter, or in the tree’s texture. Finding a bug is not enough; there has to be something about it that doesn’t fit.
But first, consider safety. Not all caterpillars are safe for handling. This helps identify which ones might sting and which might just be itchy or irritating. The graphic divides their harm into three categories: stinging, irritating, and harmless. Why does that matter? Some (the harmless) is smooth-skinned, posing no risk to people or our animals. You’ll know them by their smooth skin; you can hold them in your hand without gloves if required.
Others (irritating) are covered with barbs of some kind that tear free from the body when touched and embed in your skin. The result is red bumps and a lot of itching. No stings involved, just irritation, and again, use gloves if you must mess around with these woolly fellows. The stinging class includes those creatures whose spiky hair packs a painful punch. For instance, the Saddleback Caterpillar and the Spiny Oak Slug both has hollow spines that inject venom when touched. Immediate raised welts and a burning sensation follow. No touching with bare fingers! That’s how many gardeners learn, the hard way.
Another surefire tip-off is host plant preference. Why? Because most caterpillars are specialists, not generalists. They’ve evolved with certain trees and plants over time (think hundreds if not thousands of years). So for example, when you discover a woolly-looking caterpillar on a walnut tree, chances are good that it’s a Walnut Caterpillar. On an oak tree? Well then, maybe it’s the Gypsy Moth larva or maybe the Variable Oak Leaf Caterpillar. There are several possibilities, but at least you can cross a lot of them off the list immediately. In fact the chart reveals that more than eight different brown caterpillars feed on oaks, meaning they’re all potential targets in outbreak years. Knowing the host plant helps narrow things down considerably. There is no need to memorize every species in the world. Just the ones that feed on what grows in your yard.
Timing matters too. When do these insects emerge? Tent-making caterpillars typically form masses in spring. Webworms and tussock moths, which feed individually or in small groups, tend to appear in late summer. Before getting too close and personal with any insect, check your calendar to eliminate half of your suspects. Early instars are tiny and social, feeding on the surface of leaves till they’re see-through. As they progress, they eat whole leaves by the time they’re fully colored up.
But remember: Use these clues all at once, not separately. Look for the body shape. Look for hairiness or a lack of it. Look at the pattern of the stripes. Then think about location. Did you find it on a plant? An Eastern Tent Caterpillar will have a white stripe down its back. If it has keyhole-like spots, it’s a Forest Tent Caterpillar. A diagonal white stripe up each side mean it is a hornworm.
There are clues, and they’re there for the looking, diagnostic clues that you don’t need a degree in entomology to decipher. Just use your eyes to take notice of what nature’s showing you. Knowing what you’re looking at makes managing your garden routine less uncertain. Do I do something? Or just watch? Knowing the ID means knowing if it’s something that will be okay to ignore (some of those caterpillars won’t hurt any trees), or needs attention (to save a fruit crop, for instance, or an important ornamental plant).
You would of wanted to make sure there aren’t any more brown insects around your yard ever again. You want to know how to manage them smartly. Next time you see some strange activity in your trees, have that chart nearby. A little knowledge goes a long way to keep yourself; and your garden… Safe.