Pear slug

Caliroa cerasi

55 host plants

Last updated

Data Maturity Structured

This profile synthesizes data from multiple published sources. Expert field review is in progress.

You will find olive-green, slug-like larvae with glossy slime coating on the upper leaf surfaces of pear, cherry, hawthorn, and mountain ash trees. Feeding damage creates a skeletonized appearance as larvae consume tissue between veins. Mature larvae are orange-yellow. Multiple overlapping generations cause repeated defoliation from late April through summer. Young trees suffer the most impact.

Remove infested leaves and prune heavily damaged shoots to improve appearance. Hand-pick larvae clustering on lower canopy leaves. Spray strong water streams to dislodge small larvae. Encourage parasitic wasps and natural enemies. Time applications for May and July targeting young larvae before heavy feeding. Dormant cultivation may reduce pupae. Avoid pesticides that harm beneficial insects.

Quick Reference

Order
Hymenoptera
Type
defoliator
Host Plants
55
GDD₃₂ Emergence (est.)
4,323
Damage Severity
growth-reducing

Pear slug Emergence (est.) typically begins around 4323 GDD₃₂. As of April 23, 2026, Puget Sound stations range from 1434.4 to 1592.7 GDD₃₂, approximately 2730 units before the expected threshold.

Regional Season Tracker

GDD₃₂ accumulation across 7 Puget Sound stations · as of Apr 23, 2026
Station GDD₃₂ Current Stage Next To Go
Issaquah / East King 1,593 Pre-season Emergence (est.) 2,730
Seattle / UW 1,554 Pre-season Emergence (est.) 2,769
Kent / Auburn 1,537 Pre-season Emergence (est.) 2,786
Olympia / Tumwater 1,505 Pre-season Emergence (est.) 2,819
Bellingham / Whatcom 1,483 Pre-season Emergence (est.) 2,840
Tacoma / Puyallup 1,472 Pre-season Emergence (est.) 2,851
Sequim / Rain Shadow 1,434 Pre-season Emergence (est.) 2,889
Regional estimate

Source: Pest GDD Catalog (UMD IPMnet), Added 2026-04-03 About GDD₃₂ →

Cultural Controls

  • Natural enemies control pear slug populations fairly effectively.
  • Specific biocontrol agents are not known, but this is rarely a pest in backyard gardens, so significant biocontrol likely occurs most years.
  • Avoid use of broad-spectrum insecticides which can kill beneficial insects.
  • Wash pear slugs from trees with a strong stream of water.
  • Hand removal is effective on small trees.

Host Plants (55)

Acer crataegifolium Hawthorn, Maple Crataegus ambigua Russian Hawthorn Crataegus autumn Crataegus autumn Crataegus columbiana Columbia Hawthorn Crataegus crus Crataegus crus Crataegus douglasii Black Hawthorn Crataegus germanica Medlar Crataegus laevigata English Hawthorn Crataegus lavallei Lavalle Hawthorn, Carrierei Hawthorn Crataegus monogyna Singleseed Hawthorn, Common Hawthorn, English Hawthorn Crataegus phaenopyrum Washington Hawthorn Crataegus punctata Dotted Hawthorn, Flat-topped Hawthorn Crataegus viridis Green Hawthorn,Southern Hawthorn Prunus americana Wild Plum American (Red) Plum August Plum, Goose Plum Prunus armeniaca Apricot Prunus avium Sweet Cherry Prunus besseyi Sand Cherry, Western Sand Cherry Prunus blireiana Blireiana Plum Prunus caroliniana Carolina Cherrylaurel American Cherrylaurel Prunus cascade Prunus cascade Prunus cerasifera Cherry, Plum Prunus cistena Purpleleaf Sandcherry Redleaf Sandcherry Cistena Sandcherry Cistena Plum Prunus dream Prunus dream Prunus emarginata Bitter Cherry, Wild Cherry, Quinine Cherry Prunus first Prunus first Prunus fruticosa Steppe Cherry, European Dwarf Ground Cherry, Mongolian Cherry Prunus glandulosa Dwarf Flowering Almond Prunus ilicifolia Hollyleaf Cherry, Holly-leaved Cherry Prunus laurocerasus Cherry, Laurel Prunus lusitanica Portugal Laurel Prunus maackii Amur Chokecherry Amur Cherry, Manchurian Cherry Prunus mume Japanese Apricotc Japanese Flowering Apricot Japanese Flowering Plum Prunus newport Newport Flowering Plum Prunus okame Okame Flowering Cherry Prunus padus European Birdcherry Common Birdcherry Prunus prostrata Rock Cherry, Mountain Cherry Prunus sargentii Sargent Cherry, Sargent's Cherry Prunus serotina Black Cherry, Rum Cherry Prunus serrula Birchbark Cherry, Paperbark Cherry, Tibetan Cherry Prunus serrulata Japanese Flowering Cherry Prunus snow Prunus snow Prunus subcordata Klamath Plum, Sierra Plum, Pacific Plum Prunus subhirtella Higan Cherry Prunus subhirtella var. autumnalis Autumn Flowering Higan Cherry Prunus tai Prunus tai Prunus virginiana Prunus virginiana Prunus virginiana var. demissa Western Chokecherry Prunus virginiana var. virginiana Common Chokecherry, Eastern Chokecherry Prunus yedoensis Yoshino Cherry, Somei-yoshino Cherry, Tokyo Cherry Pyrus calleryana Callery Pear Pyrus communis Common Pear Pyrus fauriei Pyrus fauriei Pyrus salicifolia Pyrus salicifolia Rhaphiolepis indica Indian Hawthorn Rhaphiolepis umbellata Yeddo Rhaphiolepis Yeddo Hawthorn