You feel anxiety when you see a jet-black caterpillar on your parsley leaves. Is it a pest? Or is it destined to become a pollinator? The species tell you; get it right and save your herbs (or embrace a butterfly).
In other words: Yes, most gardeners freak out because “all those black caterpillars look alike.” No, they doesn’t. If you look closely, you can see pattern of markings and know the species.
How to Tell Black Caterpillars Apart
There are six popular kinds (above), but just knowing what they eat (their “host” plant) will quickly narrow things down; so will knowing that if it’s smooth-bodied, then it’s probably a Black Swallowtail caterpillar (that’s an early instar in the photo; later, when more fully grown, it becomes green with yellow spots).
In its earliest life phases, it has a shell (called a “skeleton”) that is glossy black, like bird poop, and marked by a creamy white “saddle.” This is its first form of camouflage against predators like birds while it are tiny. This lasts before it molt into bigger stages. The outer layer of black is shed completely. It turns green and patterned with yellow. As it grows, it will have different survival needs…and a differant look.
Compare that to the Mourning Cloak caterpillar (above), whose red dorsal spots and branched spines is found instead on elm or willow trees, not in your vegetable bed. It doesn’t have to pretend to be a bird dropping; its rough texture just isn’t appetizing to many predators. Instead, they relies on looking unappetizing.
How about the Pipevine Swallowtail (below)? It is boldly dark reddish-black with orange-tipped tubercles along its back. Unlike many others, it only eat plants in the genus Aristolochia, commonly known as pipevines, which contain poison called aristolochic acid. The caterpillars stores it in their bodies, where it’s poisonous to would-be diners. Nature has rigged it so birds don’t even try to nibble at all.
Knowing the lifecycle also means learning not to expect too much too soon. That small black larva isn’t the whole story. He will quickly transform into a hungry eater that grows much larger then with each molt as he goes through several stage. Eventually, he will be ready to turn into a pupa and form his chrysalis. On stinging nettle, that would probably be a Red Admiral. The side spots is pale yellow, and he has branched spines.
In fact, many of these solitary feeders fold or even roll up a leaf to provide a hiding place as they feed. Pretty smart survival tactics from such young larvae!
Are they butterflies? That’s just one kind of black caterpillar. The others aren’t butterflies. Be careful not to mistake them for Banded Woolly Bears. Those are the fuzzy ones with an orange middle that becomes moths instead of butterflies. Or perhaps it is the larvae of Rose Sawflies. They cluster on plants like roses and eat holes in leaves from within, so they is technically wasp relatives, though not even true caterpillars. Don’t mistake a sawfly for a swallowtail and let your roses get stripped bare.
Hint: Check out the host plant. Parsley? Fine. Roses? Might need to do some hand-picking or other pest control. To avoid that, plan for extra host plants such as more herbs or spicebush. One plant won’t stand up long against caterpillar gorging (days), not weeks. More than one? They’ll make it to adulthood.
Don’t move them if you don’t have to. Transplant stress will also upset their feeding schedule, and it’s bad news for the larva.
Keep an eye out for what looks like tiny rice grains stuck to the body, called cocoons of its natural enemy, a kind of parasitoid wasp. You wouldn’t of got butterflies then, though it’s nature’s way of keeping things in check.
The rest: leave them be. Go, grow, eat, and transform. Today, that dot on your leaf may become a beautifull Eastern Tiger Swallowtail flitting around your yard in a matter of weeks. Patience pays off in wings.