Bristly Rose Slug

The bristly rose slug is the larval stage of Cladius difformis, a sawfly (order Hymenoptera, family Tenthredinidae) rather than a moth or butterfly, despite its caterpillar-like appearance. It is one of several 'rose slug' sawflies that feed on cultivated and wild roses across temperate regions.

The larva gets its common name from its slightly slimy, slug-like posture and the fine, bristly hairs covering its pale green body. It feeds on the underside of rose leaves, chewing away the soft tissue and leaving a papery, skeletonized leaf surface behind.

Because sawfly larvae resemble caterpillars so closely, they are frequently mistaken for moth or butterfly larvae, though the distinction can be made by counting the fleshy prolegs along the abdomen, among other features familiar to entomologists.

• Body is pale yellow-green, tapering slightly toward the rear, with a covering of fine, short bristly hairs
• Reaches about 1.3 cm (0.5 in) in length at maturity
• Head is pale and often slightly darker than the body
• Has more pairs of fleshy prolegs than true caterpillars, a technical feature that separates sawfly larvae from moth or butterfly larvae
• Feeding damage appears as skeletonized 'windowpane' patches on rose leaves, distinct from the ragged holes made by many beetles

Found in rose gardens, hedgerows, and areas with wild rose (Rosa species) across much of temperate North America and Europe. Larvae are most active from late spring through summer, with new generations appearing through the growing season in warmer climates.

Larvae feed on the undersides of rose leaves, rasping away the lower leaf surface and leaving the upper cuticle intact, which creates a translucent, skeletonized appearance. They typically feed alone or in small, loosely associated groups rather than large aggregations. As with other sawfly larvae, they serve as a food source for birds and predatory insects, and their feeding is generally limited to the appearance of the foliage rather than the overall health of an established rose bush.

Adult female sawflies use a saw-like ovipositor to insert eggs into rose leaf tissue. Larvae hatch and pass through several instars while feeding on leaf undersides. Mature larvae drop to the soil or leaf litter to pupate in a small cocoon. Multiple generations can occur in a single growing season in warmer regions, with the species typically overwintering as a mature larva or pupa in the soil.