Munch munch munch. You know the damage. You go to the garden to admire your favorite plant and discover the leaves are missing. Who was the culprit?! Quite often it’s caterpillars!

Redhumped oakworm caterpillars

These redhumped oakworm caterpillars nibble on oak foliage.

Photo Credit: ©2004 Buglady Consulting

Black swallowtail caterpillar

The black swallowtail caterpillar feeds on dill.

Photo Credit: ©2004 Buglady Consulting

Tobacco hornworm with parasites

This caterpillar has been killed by naturally occurring parasites.

Photo Credit: ©2004 Buglady Consulting

What does a caterpillar look like?

Many gardeners are pretty good at identifying caterpillar insects as the soft-bodied larval form of butterflies and moths. The body is wormlike in appearance, but it can have “hairs.” (As some of these hairs are actually spines modified to sting, caution should be used when handling the larvae.) They come in a variety of colors, typically made up of browns to greens, and come in many patterns. Leg number varies too: Some can get around your plants just fine without having any legs at all, whereas others can have up to seven pairs. Once these caterpillars are done feeding they become butterflies and moths.

An adult female butterfly or moth mates and selects a host plant on which to deposit its eggs. The eggs can be laid singly or in groups. Once the egg hatches, the larva emerges and feeds on its host plant. Larvae go through a series of molts (shedding of “skin”) until they reach a certain size. They then stop feeding and search for a place to pupate, later to emerge from their pupal cases as winged adults.

If you’re interested in identifying your particular caterpillar pest, the best place to start is by knowing the host plant. You can perform lookups in caterpillar books or on the Internet, starting with caterpillar host plants. (Given that some species can sting, be sure you know what kind of caterpillar you’re dealing with to prevent injury.)

What kind of damage do caterpillars do?

Depending on caterpillar species, the damage can take different forms. Some caterpillars consume entire leaves, whereas others may just nibble holes in them. Some (called skeletonizers) feed on the leaf surface, scraping away the top layer and causing damage that way. Others (like leaf-roller caterpillars) attach leaves together with silk and hide within. Still other species (such as peach tree borers) can bore into the trunks of trees, sending up random branches from the trunk.

How do you control caterpillars?

Because most caterpillar insects are soft-bodied, they often fall prey to other creatures like birds, small mammals and insects. These caterpillar-eaters usually keep populations in check, but sometimes numbers can still get out of control. When this happens there are a few things you can do to slow their destructive paths:

One easy way is to just pick the caterpillars off and put them in a bucket of soapy water. (If you don’t know what type of caterpillar you’re dealing with, it’s best to wear gloves in the event that the pest is of a stinging variety.)

Another option is to use a product called Bt. Bt (or Bacillus thuringiensis) is an insecticidal bacterium. What’s great about it is it only kills caterpillars and not your beneficial insects, like ladybugs. It’s safe around humans and pests. Insecticidal soap also works as long as you spray it directly on the caterpillar. Both of these can be found at your local garden center.

Caterpillars can be good or bad, depending on your view. Many butterfly gardeners work hard to have them around, so before you squish that caterpillar, make sure it’s not going to be a beautiful butterfly!