You pull back a leaf on your favorite maple tree and there it is: yellow and fuzzy as if it’s made of tiny little angry pom-poms all balled up in defense mode. You’re probably about to poke it with a stick. Or perhaps just walk away altogether. No surprise: Yellow fuzz in the insect world are a kind of see-it-and-run visual warning label that immediately triggers some kind of caution response in most human brains: Watch out for something irritating, stingy, or worse.
But not all yellow caterpillar are after you, and getting their identities wrong can mean either needless alarm or accidental skin rashes when you go to pick up (too casually) what turns out to be a harmless species. As you can see on the chart above, there is subtle visual clues which distinguish the good guys, woolly bears, from the not-so-good (those pesky tussock moths). For one thing, it’s not only about color: It’s also the way the hairs are arranged and feel.
How to Identify Yellow Fuzzy Caterpillars
For example, tussock moths may has what look like pencil-like long, stiff bristles on each end of their body or other distinctive tufting all up there back. All these structures are meant to easily pop off, then get embedded into your skin, producing welts and itchiness that can persist for days. Woolly bear and tiger moth caterpillar usually have an even coating of soft fur resembling velvet rather than bristles. Despite their scary-looking appearance, they’re typically non-threatening when touch by people.
That explains why you’re seeing them when you are: In most of these species, one generation per year are the norm, so what you’re seeing as caterpillar in late summer is weeks-in-the-making, starting out from eggs deposited in springtime. At their final, larval life stage, it’s go-go-go time for them, as they consume virtually all their calories to save up for the pupal phase ahead. That’s why they can suddenly defoliate such a tree so dramatically, such as an oak or sycamore that is there host. If there is a large colony present, they can strip a branch bare in just days, leaving nothing but leaf veins. They also leave behind heaps of frass, which are their tiny pellets of waste and a clear sign of active feeding overhead.
First things first: Before using any controls, identify your culprits if possible. Examine their pattern and coloration, including even the color of the head capsule. Dark-striped bodies with a yellow neck ring indicate the yellow-necked caterpillar, a tree-dweller of note for oak and apple trees in particular. Black tuft-surrounded bright yellow bands signal a spotted tussock moth (a poplar and maple favorite). Then there’s where they’re located…woolly bears confine themselves to low garden plants such as dandelions, clover and other ground-level food, while sycamore tussock moths basically lives only on sycamore trees. In most cases, they don’t pose much of a threat to your vegetable crops.
First: Observe, don’t eradicate. Most of these caterpillars is an important food source for birds. Some bird species, such as orioles and cuckoos, will even eat them as one of their only food sources because they can tolerate the stinging hairs well. Generally, it is better to let nature take its course by using fewer broad-spectrum pesticides and encouraging natural predators to do there work, rather than trying to kill every single larva.
When you have a treasured plant that really needs some help, there are organic options such as Bacillus thuringiensis, aka Bt spray, that are safe for bees and other good guys but deadly to specific caterpillars; they are organic. If there is a small infestation, you might want to just remove the larvae by hand (again, wearing gloves). Be sure to drown them in a tub of soapy water instead of just dropping them on garden ground.
So in conclusion: Pay attention to the details first, then react. If you know what to look for, the hair structure and the host plant; you can avoid unnecessary worry (or a rash-causing mistake). Those yellow fuzzy things visiting get easier to identify once you know that’s the stiff bristle of a tussock moth and not the soft fur of a woolly bear. Then they don’t seem so threatening, just another recognizable part of the garden ecosystem that follows its own predictable pattern.
The next time you see one, pause and have a look before leaping into action. Or rather, putting on the gloves.