Jennifer is a gentle soul; a massacre just isn’t in her nature. So I was surprised when she asked if she must kill them all.
I can’t blame her for having post traumatic caterpillar stress disorder after the last few years of winter moth madness. She was worried about her trees and called to ask if she must slay the black and orange beasts to protect her oaks.
The beasts in question are orange-striped oakworms, caterpillars that have been seen recently in large numbers feasting on oaks, moving along roads and bike paths, and generally striking fear in the hearts of tree lovers everywhere. These caterpillars are relatively easy to identify. They are a smooth, hairless black caterpillar up to two inches long with eight orange-yellow stripes. Look for two long curved horns behind their head and if you get close, observe the black short spines on their bodies.
There is another caterpillar that you might confuse with the orange-striped oakworm, called the yellow-necked caterpillar. The difference is in their behavior. If you shake the leaf that they are on, the yellow-necked caterpillar will raise its head to see who or what is bothering it. The orange-striped oakworm will ignore you and continue to eat. It makes sense that this caterpillar has been referred to as a “stomach with legs.” Almost nothing can interfere during mealtime, and mealtime is all the time for the orange-striped oakworm.
By the time you notice these caterpillars, it is late in their life. They start off as small, green nondescript caterpillars and typically it is the copious amount of frass, or caterpillar droppings, that clue you in to let their presence. They are considered pests, but differ from those other caterpillar vermin in many ways.
So to answer Jennifer’s question, no you don’t have to kill them. While they do have the ability to harm and even kill the young and weak trees in your yard, they are not as destructive as the winter moths, gypsy moths, and Eastern tent caterpillars that have plagued the island over the last few years. They differ from those demons in a few ways.
One important difference is that oakworm caterpillars defoliate in the fall when natural cycles dictate that trees will lose their leaves anyway. And outbreaks of the native oakworms rarely last more than two years, due to the presence of natural enemies such as birds, parasites, and other insects. One resource suggested a natural way to control oakworms by installing a paper wasp nest! It seems like trading one pest for another, but I guess it depends on your priorities and proclivity to get stung.
Those other caterpillars, winter moths and their ilk are non-native species and there is a lack of predators to keep their populations in check. Additionally, they defoliate in the spring when they can do the most damage to the leaves, buds, and general health of the trees. Add to that their ability to balloon, or move via a silken thread carried by the wind. Simply put, all bad.
Since the orange-necked caterpillar doesn’t bow to those dirty deeds, you can be a bit more patient and let nature take its course. As I told Jennifer, take a laissez-faire attitude when it comes to the orange-striped oakworm. My advice in this case is to live and let live.
Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown.