Although given the common name "slug", these critters are actually insects which are the larvae of types of sawflies. In the larval stage, they resemble tiny slugs that are slithering around on leaves with the help of a secretion from their bodies. At their maximum, they are about 3/4 inch in length and are shiny yellow-green in color.

After feeding on the leaves for several weeks, the larvae fall to the ground to pupate into the adult sawfly. They may go through a second generation later in the summer. Some species may have up to 6 generations per year.

Sawfly larvae feed on the underside of plant leaves leaving behind the papery, translucent surface and the leaf veins. Generally, the damage is not severe and is considered cosmetic in nature.


1. Check the Plants for Infestation - Inspect the bottom of leaves and look for damage starting in mid-spring. In cases of light infestation, you can simply remove the critter manually or spray with an insecticidal soap which will melt the waxy coating on its soft skin making it dehydrate and die.

2. Natural Enemies - Predaceous beetles, certain parasitic wasps and a few fungal diseases help to keep rose and pear slugs in line. Of course, like all natural approaches, this will not totally eliminate the problem...just mitigate it. You will need to minimize the use of stronger insecticides (soaps are o.k.) to avoid killing these good guys too.

3. Use an Insecticide - In cases of severe infestation, it might be necessary to use regular pesticides for the control of these insects. This should be the rare case, however.

4. Bt Won't Work - Even though these critters look like caterpillars...they are NOT. Since they are the larval form of a sawfly (like European pine sawfly), the insecticide, Bacillus thuringiensis (Bt) will not work on them. Bt kills caterpillars that become moths or butterflies.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

Types of Insects

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