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Description and Biology

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Pear slugs, Caliroa cerasi, are also called pear sawflies and cherry slugs. These caterpillars are called slug caterpillars because they appear wet or shiny with a sort of greenish slime. Plus their legs are so short that they do resemble true slugs in top view, but they are slightly wider at the head end. Pear slugs are the immature stages of a small, shiny black, fly-like insect — the pear sawfly — that uses its saw-like ovipositor to pierce leaves to lay eggs inside (hence the name sawfly) most often in the upper canopy. Females are almost 3/16 inch long and black with brownish feet and lower legs. The translucent, dark wings are held flat over the back. Males are similar, but slightly smaller. The egg is very small, oval, tan, and looks like a small blister on the leaf. Eggs are laid in the upper leaf surface and hatch in 10 to 15 days. Newly hatched and newly molted pear slugs bare and yellow before they secrete their slime. Fully grown pear slugs are about 3/8 inch long and are slimeless and yellowish orange. They drop to the soil where they dig in 2 or 3 inches and spin a tough silken cocoon in which they eventually pupate later in the summer or in the next spring. From the cocoons emerge another generation of adult pear sawflies that continue the wheel of existence. At least two generations occur each growing season. The second generation is usually the most damaging.

Pear sawflies

Pear sawflies are about the size of a house fly.

pear slug eggs

Since pear sawflies lay their eggs in the top of the leaf, I take Lesley Ingram's word for it that there are pear slug eggs.

Pear slug

Pear slugs grow to about 3/8 to 1/2 inch long.

Pear slugs have 10 pairs of legs.

Pear slugs have 10 pairs of legs.

Host Plants

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Pear slugs feed on the upperside of leaves of pear, cherry, hawthorn, plums, quince and occasionally apple where they skeletonize the leaves (eat everything except the veins, leaving a skeleton of the leaf behind). Eggs are sometimes laid on peach leaves, but pear slugs don't seem to do well on peach. Heavily infested trees turn brown, and leaves wither and drop. Defoliation can weaken the tree.

Trees heavily damaged

Trees heavily damaged by pear slugs may drop their leaves prematurely.

Residential Recommendations

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Pear slugs are reportedly susceptible to insecticides. Orthene, Sevin or some other insecticide labeled for use on landscape plants should give adequate control.

Other Resources

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For assistance with a specific problem, contact your local Cooperative Extension Center.

This Factsheet has not been peer reviewed.

Author

Professor Emeritus
Entomology & Plant Pathology

Publication date: May 25, 2019
Revised: Jan. 9, 2019

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