Pear slugs are not actually slugs. They’re the larvae of a small sawfly (Caliroa cerasi) that feed on the leaves of pear, cherry, and several other fruit and ornamental trees. Covered in a dark, slimy coating that makes them look remarkably like tiny slugs, these olive-green to black larvae scrape the surface of leaves, leaving behind a distinctive skeletonized pattern. The good news: in most cases, the damage is cosmetic and won’t threaten your tree’s health.
What Pear Slugs Look Like
The larvae are what you’ll notice first. They’re small, tadpole-shaped, and coated in a dark greenish-black slime that gives them their slug-like appearance. They’re wider at the head end and taper toward the tail, typically reaching about half an inch long at maturity. You’ll usually find them on the upper surface of leaves, often several on a single leaf.
The adult form is a small, shiny black sawfly, a type of wasp-like insect that doesn’t sting. Adults are only about 5mm long and easy to overlook. Most gardeners never see them, only discovering the infestation when damaged leaves catch their eye.
Trees They Target
Pear and cherry trees are the preferred hosts, but the list of susceptible plants is longer than most people expect. Pear slugs also feed on plum, prune, quince, apricot, hawthorn, cotoneaster, and mountain ash. Eggs are sometimes laid on peach leaves, particularly when peach trees grow near infested pear or cherry orchards, but the larvae don’t survive well on peach foliage.
How They Damage Leaves
Pear slugs feed exclusively on the upper surface of leaves. They scrape away the soft green tissue between the veins while leaving the veins themselves intact. This creates a characteristic “skeletonized” look, where the leaf takes on a lacy, see-through appearance. Heavily fed-on leaves turn brown and shrivel up.
Despite how alarming this can look, damage from pear slugs is generally cosmetic and will not harm the overall health of the tree. A mature tree can tolerate significant leaf surface loss without a major impact on fruit production. Young trees or small ornamentals with heavy infestations are more vulnerable, since they have less leaf area to spare and rely on every leaf for growth energy. If most of the canopy is affected on a young tree, it’s worth stepping in.
Life Cycle and Timing
Adult sawflies emerge in late spring and lay eggs inside leaf tissue, where they’re hidden from view. The larvae hatch and begin feeding on the leaf surface, growing through several stages over a few weeks before dropping to the soil to pupate. In many climates, there are two generations per year. The first appears in late spring to early summer, and a second, often larger generation feeds in late summer. The second generation tends to cause more visible damage because it arrives when trees have already been stressed by summer heat.
Pupae overwinter in the soil beneath the tree, emerging as adults the following spring to restart the cycle.
Simple Control Methods
For most home gardeners, the easiest approach is physical removal. Because pear slugs feed on the upper leaf surface and move slowly, you can knock them off with a strong jet of water from a garden hose. The slimy larvae can’t easily climb back up. On small trees, you can simply pick them off by hand (they’re harmless to touch, just slimy).
Dusting affected leaves with wood ash or diatomaceous earth is another old, effective trick. These dry, abrasive materials strip the protective slime coating from the larvae, causing them to dehydrate and die. A light dusting on the upper leaf surfaces where the larvae feed is all it takes. Reapply after rain.
Because the larvae pupate in shallow soil beneath the tree, lightly cultivating the soil under the canopy in late fall or early spring can expose and destroy overwintering pupae. This won’t eliminate every one, but it can reduce the population for the following season.
When Spraying Makes Sense
On larger trees or in orchards where physical removal isn’t practical, insecticidal soap is an effective low-toxicity option. It works on contact, breaking down the larvae’s protective coating. Spray the upper surfaces of affected leaves, since that’s where the larvae feed.
For heavier infestations, spinosad is a biorational insecticide derived from soil bacteria and is approved for use on organically grown produce. It’s effective against pear slug larvae and has a relatively short waiting period before harvest (7 days for pears). To avoid the larvae developing resistance, don’t use spinosad-based products more than twice in a row. Alternate with a different type of treatment between applications.
Commercial growers use a threshold of about 25% of sampled leaves being infested before applying targeted treatments. For home gardeners, this translates to a simple check: if a quarter or more of the leaves you look at have larvae or feeding damage, treatment is worthwhile. Below that level, the tree will handle it on its own.
Preventing Repeat Infestations
Pear slugs tend to return year after year because they overwinter right in the soil beneath the trees they fed on. Keeping the area under your tree clean and cultivated disrupts this cycle. Encouraging natural predators helps too. Parasitic wasps, predatory beetles, and birds all feed on sawfly larvae. Avoiding broad-spectrum insecticides in your garden protects these beneficial species and lets them do some of the work for you.
Healthy, well-watered trees tolerate pear slug damage far better than stressed ones. A tree that loses some leaf surface to skeletonization in July can compensate if it has adequate water and nutrition. The combination of good tree care and occasional physical removal is enough to manage pear slugs in most home gardens without ever reaching for a spray bottle.