Something green is on your tomato plant, a big fat worm, and oh no! Panic! Spray! Grab whatever’s handy and douse it, thinking: Any crawler on my food is an enemy, and I must get rid of it. That’s what will kill your garden (faster than anything else). Here’s why: Most green worms (caterpillars) is not enemies; they’re moths and butterflies in the making. In fact, they are vital part of your local ecosystem.
A few are harmless guests, dining on neighboring woodlot trees. Others will strip a plant down to nothing overnight if left unchecked. Knowledge about them save money, preserves beneficial insects, and helps keep the garden growing, and doesn’t turn it into a chemical warfare zone.
Identify Worms Before You Spray
Before we do anything, let’s first observe what we’re dealing with: A good place to start is this visual ID guide, which identifies common pests (and some non-pests) that confuse many home gardeners. Instead of merely responding to motion, take a closer look at markings and body shape.
Tomato hornworm, for instance, a voracious foliage-eater and good hider in the leaf canopy, reach impressive size and has telltale diagonal white stripes along its sides. When you spot them, the best tactic may be to simply pinch them off instead of using spray. This is a great way to handle those larvae, because they are often filled with parasitic wasp larvae that you would of like to see survive. That’s why you’ll sometimes see little white cocoons on their back, natural helpers already doing the job for you. Don’t blast them with broad-spectrum pesticides; promote that biological control instead.
Compare that voracious eater to the parsley worm, which live on fennel or dill plants. Its bright-yellow-and-black banding makes it look fierce, but it’s merely larval stage of the beautiful black swallowtail butterfly. Any damage done by a few is typically minimal and strictly cosmetic. It is better to let a few go to caterpillar heaven. You can watch them turn into adult butterflies that will flutter about your yard all summer long. A couple of handfulls of missing parsley leaves for this? It is a bargain. It is far more valuable than a few leaf.
The chart sorts out who’s who, what’s a pest and what’s a beneficial garden guest, and helps you separate the two kinds of behavior. CATERPILLARS often limit themselves to certain plant families, so knowing your host plants will help with ID a lot: Imported cabbageworm (and other worms) and cabbage loopers is prime suspects if you’re having trouble with kale or cabbage. Or any brassica crop. They’re serious pests, and should be dealt with, but are easy to manage organically if tackled early in the season with Bacillus thuringiensis. Better yet, use row cover before sowing to stop them from laying eggs completely. Nothing chemical is needed; just a physical barrier, and it’s always wiser to take a preventive step against pests instead of running behind an infestation once it begins.
Many green larvae (caterpillars) that you see on ornamentals and fruit trees aren’t a problem at all. The ones that devour birch and walnut trees is Luna moth caterpillars, for example. They don’t harm any vegetable crop, get really big and create one of North Americas prettiest moths. Let them be; it’s good for local biodiversity, and they’re part of what makes things interesting in the landscape. If they chew a few leaves, so what? Trees are strong enough to take such small losses. Balance, not eradication, is what we want.
Begin patrolling plants instead of reacting after disaster strikes. If it’s early (and easiest to handle), check for eggs and tiny larvae on underside of leaves. Moths and butterflies has different numbers of legs; knowing this will clue you in to what their grownup selves look like. Some eat at night; shine a light outdoors then, such as with a flashlight, to reveal who is hiding by day.
You’ll be part of the natural balance of the garden, not its enemy, if you take time to get to know it and be patient. Go from blindly spraying to eyes-wide-open watching. That next green worm may be someone you want to make friends with.