Pests in Gardens and Landscapes: Quick Tips

Leaf-feeding Caterpillars

Published   4/17

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Caterpillars, the larvae of butterflies and moths, damage plants by chewing on leaves, flowers, shoots, and fruit and sometimes by boring into wood. Caterpillars in fruit or wood can be difficult to manage: they are hidden most of their life and can cause serious damage even when numbers are low. However, many plants, especially perennials, can tolerate substantial leaf damage, so a few leaf-feeding caterpillars often aren’t a concern. Handpicking and natural enemies often provide sufficient control.

Early detection and removal prevent excessive damage.

  • Look for feeding holes, excrement, webbed or rolled leaves, caterpillars, eggs, and natural enemies.
  • Prune off rolled or webbed leaves, and handpick caterpillars from plants, destroying the insects by crushing them or by dropping them into soapy water.

Caterpillars have many natural enemies.

  • Beneficial insects and other organisms often prevent caterpillar numbers from rising to damaging levels.
  • Most caterpillar species have several species of parasitic wasps or flies that attack them. Look for parasite cocoons next to caterpillars, darkened caterpillar eggs, or exit holes in dead caterpillars.
  • General predators include birds, assassin bugs, lacewings, predaceous ground beetles, and spiders.
  • Naturally occurring diseases caused by viruses, bacteria, or fungi often kill caterpillars.

Less toxic insecticides are available.

  • Use insecticides only when damage is intolerable, nonchemical methods haven't worked, and smaller caterpillars are present. Avoid insecticides that can kill beneficial insects, and don't treat butterfly garden plants, otherwise you'll kill the caterpillars that will become butterflies.
  • Bacillus thuringiensis subspecies kurstaki (Btk) is a microbial insecticide that kills only caterpillars. It’s safe to use near bees, beneficial insects, and wildlife. Caterpillars must feed on treated leaves to be affected. Because it’s most effective on small, newly hatched caterpillars and breaks down rapidly, treatment timing is critical.
  • Spinosad is a safe microbial-based insecticide, but it can have negative impacts on some beneficials.

Some common leaf-feeding caterpillar species:

Hollow stem damage caused by rapid growth disorder.

Beet armyworm is a common pest on vegetables and flowers. Yellowstriped armyworm is similar but dark with yellow and orange stripes.

Hollow stem damage caused by rapid growth disorder.

A parasitic wasp lays her egg in an armyworm. The egg will hatch into a larva that will feed inside the armyworm and kill it.

Hollow stem damage caused by rapid growth disorder.

Tobacco hornworm on tomato. Note its excrement on the leaf below.

Hollow stem damage caused by rapid growth disorder.

The western tussock moth feeds on many ornamental and fruit tree species.

Hollow stem damage caused by rapid growth disorder.

Leafrollers, such as this fruittree leafroller, feed inside leaf rolls secured with silk and, when disturbed, often drop to the ground, hanging from a silken thread.

Hollow stem damage caused by rapid growth disorder.

The cabbage looper has three pairs of prolegs in the back and fewer in the middle, causing it to move in its typical looping pattern.

Hollow stem damage caused by rapid growth disorder.

Fall webworms feed in groups within silken tents. Many tent caterpillars create similar nests. Prune these out and destroy them.

Hollow stem damage caused by rapid growth disorder.

Egg cluster and newly hatched larvae of the redhumped caterpillar. As these larvae mature they will develop a bright red hump just behind their head.

Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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