Pest profile

California Oakworm

Phryganidia californica · Lepidoptera: Notodontidae[2]

The California oakworm is the most important oak-feeding caterpillar along the California coast, but healthy oaks tolerate even heavy defoliation.[1]

California oakworm caterpillar with dark and yellow lengthwise stripes and a large brown head, on oak bark
California oakworm caterpillar with dark and yellow lengthwise stripes and a large brown head, on oak bark. Photo: Alex Heyman, public domain (CC0), via iNaturalist

How to identify it

  • Older caterpillars are commonly dark with prominent lengthwise yellow or olive stripes and a large brown head, about 1 inch long.[1]
  • Young caterpillars are small and yellowish green with dark side stripes.[1]
  • Adults are tan to gray or silvery moths with prominent wing veins and about a 1-1/4 inch wingspread.[1]
  • Pupae are white to pinkish with black marks, hanging from limbs, trunks or nearby objects.[1]

Look-alikes

Look-alikeHow to tell them apart
Tussock moth and tent caterpillarsThese also feed on oaks but are quite hairy; oakworms are relatively smooth.[1]

Where it lives

It ranges along the coast and coastal mountains of California; damage is most common on coast live oak around San Francisco and Monterey bays.[1]

US map: public records from 2 states since 1990 (GBIF).

Biology and life cycle

Fall eggs hatch within weeks, and caterpillars overwinter on evergreen oak leaves, pupating in May or early June.[1]

Moths emerge in June and July, and a summer generation feeds July through September; a third generation can occur in warm areas.[1]

Damage and signs

  • Young caterpillars skeletonize the leaf surface, and older ones chew through whole leaves.[1]
  • Populations swing unpredictably from very high to undetectable.[1]

Health risk

It feeds on oaks; UC IPM mentions no risk to people.[1]

Control

Prevention

Treatment usually isn't recommended; healthy oaks generally tolerate extensive defoliation.[1]

Biological control

Predators, parasites and natural disease outbreaks sometimes kill enough oakworms to control them.[1]

Common questions

Is the oakworm going to kill my oak?
Unlikely; healthy oaks generally tolerate extensive leaf loss without serious harm.[1]
Why are moths fluttering around my oak in summer?
Oak moths from the summer generation fly around oaks in the late afternoon in June and July.[1]

Sources

  1. University of California Statewide IPM Program, “Pest Notes: California Oakworm (Publication 7422).” ipm.ucanr.edu/PMG/PESTNOTES/pn7422.html (accessed 2026-10-06)
  2. iNaturalist, “Phryganidia californica taxon page (order and family).” www.inaturalist.org/taxa/83958 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.