Pest profile

Pear Slug

Caliroa cerasi (pear sawfly, cherry slug) · Hymenoptera: Tenthredinidae[2]

Pear slugs aren't slugs at all. They're sawfly larvae coated in olive-green slime that skeletonize cherry and pear leaves.[1]

Pear slug, a shiny black slug-like sawfly larva, on the upper surface of a green leaf
Pear slug, a shiny black slug-like sawfly larva, on the upper surface of a green leaf. (c) Alexandria 'Alex' Wenninger, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Larvae grow to about 3/8 inch and are covered with a gelatinous, olive-green coating that makes them look like small slugs.[1]
  • The thorax behind the head is wider than the rest of the body.[1]
  • Larvae have seven pairs of prolegs, more than the five or fewer of most caterpillars.[1]
  • Adults are glossy black and yellow sawflies about 1/5 inch long with a broad waist.[1]

Look-alikes

Look-alikeHow to tell them apart
California pear sawflyIts larvae are bright green and lack the olive-green slimy coat.[1]

Where it lives

It feeds on cherry and pear and also cotoneaster, hawthorn, mountain ash, plum and quince; in California damage is mostly in coastal and northern areas.[1]

US map: public records from 17 states since 1990 (GBIF).

Biology and life cycle

Mature larvae overwinter in cells in topsoil and emerge as adults in early spring.[1]

Females insert eggs in the undersides of leaves, and larvae pass through five instars.[1]

There are generally two generations a year, with larvae most common in mid to late spring and mid to late summer.[1]

Damage and signs

  • Larvae chew the upper leaf surface down to the veins, leaving brownish to gray patches.[1]
  • Heavy summer feeding can shrink fruit that year and the next, but it doesn't threaten healthy plants.[1]

Health risk

It feeds on leaves; UC IPM describes no risk to people.[1]

Control

Traps and physical control

When numbers are low, pick them off or wash them off with a strong stream of water.[1]

Pesticides

Thorough sprays of horticultural oil, neem oil, insecticidal soap or spinosad control them; don't spray spinosad on flowering plants.[1]

Bt does not work on sawfly larvae, because they aren't caterpillars.[1]

Common questions

What are the slimy black slugs on my cherry leaves?
They're pear slugs, sawfly larvae with a slimy olive-green coating, not true slugs.[1]
Will Bt kill pear slugs?
No. Bt only affects caterpillars, and sawfly larvae aren't caterpillars.[1]

Sources

  1. University of California Statewide IPM Program, “Pear Sawfly (Pearslug) (Pests in Gardens and Landscapes).” ipm.ucanr.edu/PMG/GARDEN/FRUIT/PESTS/pearslug.html (accessed 2026-10-06)
  2. iNaturalist, “Caliroa cerasi taxon page (order and family).” www.inaturalist.org/taxa/386969 (accessed 2026-10-06)

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