Key Features

  • Defoliation
  • Holes in Leaves
  • Worm-like hairy or hairless body
Catalpa worm caterpillars
Forest tent caterpillar
Swallowtail caterpillar


Caterpillars are the worm-like immature stages of butterflies and moths that can chew foliage, or feed on wood beneath the bark of a tree. They can be smooth or hairy, brightly or dull colored. They can completely consume leaves and defoliate plants. They are distinct from another groups of worm-like larvae called sawflies, a kind of plant eating wasp that cannot be killed by applications of a biological pesticide called Bacillus thuringiensis. Caterpillars are distinguished from sawflies by having 2-5 pairs of prolegs beyond the true legs. Each of these legs are capped with small barbs, called crochets. Sawflies have 6 or more pair of prolegs.

Bayberry caterpillar feeding on buds in spring
Tussock moth
Young caterpillars scrape away top of leaf surface


Caterpillars are the worm-like immature stages of butterflies and moths. This is the stage of moth that will defoliate trees, mine leaves, or bore beneath tree bark. Caterpillars do the most feeding and also are easiest to control. Eggs are usually laid as a mass that eventually hatches into small larvae that consume ever increasing large pieces of leaf. Depending on the species caterpillars, they usually have between 1-3 generations a year.

Looper caterpillar feeding on rose
Pandora sphinx moth wandering on branch
Parasitic wasp laying egg in yellownecked caterpillar

Management Recommendations

Most products are most effective when directed against small, young caterpillars. To prevent late season outbreaks of spider mites, early season caterpillars should be controlled with a biorational pesticides like the bacterium Bacillus thuringiensis, 'Kurstaki' (BT), spinosad (Conserve), chlorantraniliprole, azadirachtin, diflubenzuron,or tebufenozide. Other insecticides that work on later stage caterpillars include pyrethroids (bifenthrin, fluvalinate, permethrin, resmethrin) and carbaryl, and acetamiprid. To protect bees do not apply foliar insecticides when trees are flowering.

Effective Pesticides

Active Ingredients include: Azadirachtin, Bacillus thuringiensis var. Kurstaki, Bifenthrin, Carbaryl, Chlorantraniliprole, Cyfluthrin, Fluvalinate, Permethrin, Spinosad, Tebufenozide

landscape report
Purdue Landscape Report
Plant & Pest Diagnostic Laboratory