First it shows up on a parsley leaf. It is small, black, and looks like bird poop. Is it an insect? Is it a pest? You’d better make sure you don’t wash it off or pluck it with tweezers. That’s no pest; that might be the larval form of a Black Swallowtail butterfly, which will become one big pollinator in July. Nothing harmful to people; in fact, they can be touched.
If you’re a new grower, that larva is easily mistaken for some kind of villain. Markings and texture matters more than color. Why do the caterpillars comes in dark colors? Some are trying to hide, blending in with leaf litter or the bark of trees. Others, like this one, are sending out a warning: I am not good to eat. The chart above show how dangerous each species is.
How to Identify Black Caterpillars in Your Garden
Look carefully; some irritating moth larvae, such as the tussock moths shown below, is easy to distinguish from those safer swallowtail cousins. If their body is smooth, go ahead and pick them up; if hairy, leave well enough alone. The Spongy Moth caterpillar (above) have those distinctive blue and red dots along its back, but that doesn’t mean it’s safe to touch; it can cause a rash.
Other good signs are host plants: It’s probably a swallowtail if you’re seeing the larva on, say, fennel or dill. Early on, those larvae resemble bird poop (and thus evade predators). Later they become green with yellow spots, but by the black stage, well, they can take care of themselves.
With your tomato seedlings, watch out for other troublemakers. Is there a smooth black worm curled up in a C shape? That’s probably a Black Cutworm. The pests spends their days hiding in the soil, then at night come out and chew off the stem right near the ground level. These guys don’t care about looking nice; they do efficient work.
There are telltale signs, but identification is tricky because there is look-alike moths (including some whose larvae have a dark, fuzzy appearance). Like the Woolly Bear? That’s an all-black caterpillar with no orange band to make it famous for predicting the weather. And no: it’s not eating any vegetable crops; just clover and other weeds. Does the larval form of a Mourning Cloak has a spiny structure and red spots? Yes (but those spikes aren’t real); they’re harmless bluffs meant to resemble snakes or other stinging plants like nettles.
These signs changes how you manage a garden. Suddenly, you don’t view everything crawling around in black as enemy. ID IS THE KEY to management. Swallowtail larvae? Eat some leaves of your herbs; get butterflies who contribute to pollination. Cutworms among your transplants? Nematodes or collar. Tussock moths? Don’t mess with them except where it’s too many; then they’ll feed the local food web.
Not all insects are bad. They are just the ones you don’t want in your crops. Know which is which. Most black caterpillars are simply eating to change. Examine the texture. What are they eating? Before responding. That’s good for the crop and for pollinators. A black dot may be the start of something beautifull.