Are Caterpillars Good for a Vegetable Garden?

Beauty is not the only quality in the eye of the beholder. "Good" and "bad" -- when applied to insects in the garden -- also depend entirely on who is calling the shots. Although caterpillars chow down on tender green shoots and vegetables in a garden, some grow into useful butterflies and moths that help to pollinate the garden and the world.

"Nothing's quite as sure as change," the Mamas and Papas sang a few generations ago, and it could serve as the national anthem of butterflies and moths everywhere. The relatively short lives of these fliers are marked by a metamorphosis from egg to winged pollinator.

Each species has its own particular story, but most moths and butterflies pass through four distinct stages of development: from egg to caterpillar to pupa to adult. The caterpillar stage is the eating stage, and it is the job of the insect -- when it is long and cylindrical -- to ingest as much food as possible to keep the pupa supplied with energy until metamorphosis. At that point, the butterfly or moth emerges to aid the world by pollinating flowering plants.

Butterflies and moths are champion pollinators, carrying pollen from male to female plants or from one complete flower to another in their quest for nectar. Many plants depend on these flying pollinators to propagate. Generally, butterflies take the pollination day shift, and moths go to work from dusk through dawn, although a few moths -- such as the hummingbird clearwing -- are active while the sun is up.

Butterflies and moths are widespread, with butterflies on all continents except Antarctica. Although moths and butterflies are not as efficient pollinators as bumblebees or honeybees, these winged insects make up for the smaller amount of pollen they carry by their frequent visits. Butterflies prefer big, colorful flowers while any flower that becomes fragrant at dusk probably requires moth pollinators.

Think of caterpillars as the ugly ducking stage of butterflies and moth development. If all caterpillars were suddenly evicted from planet Earth, butterflies and moths also would disappear, and with them the plant species that need them for pollination.

Many kinds of caterpillars inflict damage on vegetable garden plants in their quest for food. It is important, however, to try to identify those that will become beneficial insects and allow them safe haven rather than simply bringing out the pesticide spray.

Gardeners may not like caterpillars that mow through garden vegetables, but in time those insects become the nectar-feeding butterflies and moths that pollinate the same plants they defoliate. Those caterpillars include hornworms (Manduca spp.), loopers (Trichoplusia ni, Autographa precationis and Pseudoplusia includens) and armyworms (Pseudaletia unipuncta or Spodoptera frugiperda).

If you are determined to get rid of some of the caterpillars in your garden, take the time to learn ways to identify those that become pollinators in the future. One simple rule of thumb is that a caterpillar longer than 3 inches is very likely to be the larva of a butterfly or moth. In fact, the larger the caterpillar, the more likely it is to be a future pollinator.

If, for example, you come upon a roughly 5-inch-long, dull-green caterpillar with orange and black spines, you are likely looking at the larval stage of the regal moth. The imperial moth larvae is 4 inches long, its body green or brown with tiny white hairs on it, and its head yellow.

Many conservation organizations or plant protection programs provide charts or descriptions of these "beneficial" caterpillars. It pays to take a look and learn about the creatures that share your garden.