First, you see them, then you don’t. The glossy new leaves on your dwarf fruit tree vanish overnight. The mahogany-colored foliage on your prize rose is suddenly shredded. Even the tough, leathery leaves of a California live oak show heavy chewing. A closer look reveals little more than ragged leaf edges and missing tissue. Chances are one or more types of caterpillars are feeding while you sleep.
Caterpillars:
- Are the larvae of moths and butterflies.
- Can cause noticeable damage in a very short time.
- Are herbivores but feeding habits vary widely.
- Chew holes or completely consume leaves
- Roll or fold leaves together with silk for shelter
- Create silken “nests” in foliage
- Feed on stems, roots, or mine inside leaves
- Cause damage that can range from cosmetic to severe defoliation that leads to branch dieback or plant death
Common foliage-feeding caterpillars in our area
- California oakworm (Phryganidia californica) – feeds on oak trees
- Western tussock moth (Orgyia vetusta) – attacks many evergreen and deciduous trees
- Western tent caterpillar (Malacosoma californicum) – prefers deciduous trees and shrubs
- Omnivorous looper (Sabulodes aegrotata) – feeds on many ornamentals
- Fruittree leafrollers (Archips species) – damage fruit trees and ornamentals
Life cycle basics
- Eggs are laid on host plants, either singly or in masses
- Larvae hatch and begin feeding immediately
- Caterpillars grow rapidly, shedding their skin several times
- After pupation, adult moths or butterflies emerge
- Some species have one generation per year; others have several, causing repeated damage
Management and control
- Mechanical removal
- Prune and dispose of infested foliage (do not compost)
- Scrape egg masses from bark into soapy water
- Encourage natural predators
- Birds, beneficial insects, and parasites help suppress populations
- Biological control
- Apply Bacillus thuringiensis (BT) when larvae are small
- BT targets caterpillars only and is safer for beneficial organisms
If damage appears overnight, inspect plants after dark with a flashlight—you may catch the culprits in the act.