Sawflies are a group of insects in the suborder (Symphyta) of the Hymenoptera (bees, ants and wasps). There are about 500 species of sawfly in Britain. They have caterpillar-like larvae that feed on plant material and are named after the saw-like egg laying organ used by females to lay eggs in plant material. Adults can come in a range of colours many are black, green, orange or striped yellow and black. Most are small (< 1 cm) but some species such as the Birch sawfly (Cimbex femoratus) can be over 2 cm long. Several species can be found in gardens and are part of the biodiversity a healthy garden will support. More information can be found at The Sawflies of Britain and Ireland webpages.

Large rose sawflies have pale spotted black, green and yellow larvae that eat the leaves of roses, sometimes causing severe defoliation. The adults have orange/yellow abdomens with a mainly black thorax and heads.

Roses are also food plants for a range of other sawflies such as the rose leaf-rolling sawfly and rose slug sawfly or slugworm.

You may see the following symptoms:

• The female sawflies lay eggs in soft young rose stems, they can sometimes be found with their orange rear ends inserted in the stems. The stems often split open where the eggs were laid, resulting in elongate scars
• Whitish green, caterpillar-like larvae with black spots and yellow blotches can cause defoliation in early and late summer

Sawflies are a part of the biodiversity a healthy garden supports. Healthy roses can cope with some defoliation and the presence of some larvae can be tolerated.

• Where possible tolerate populations of sawfly; plants often recover from defoliation and roses are a food plant for several sawfly species
• Encourage predators and other natural enemies of sawfly in the garden, such as birds, wasps and ground beetles
• Check plants regularly from May onwards for the presence egg laying females, egg scars and larvae, to prevent a damaging population from developing. Eggs within the scars can be destroyed by running a fingernail (or equivalent) down the scar
• Remove larvae by hand if required and where practical

In Britain there are two species of large rose sawfly: Arge pagana and A. ochropus. The adult insects of both species have yellow abdomens with the legs, thorax and heads being mostly black. Arge pagana is the more common species. 

Rows of eggs are inserted into soft young rose shoots and female sawflies are sometimes seen dangling from such stems, attached only by their saw-like egg-laying organs.

After hatching, the larvae feed together in groups. They are pale green with black spots and yellow blotches, and are up to 25 mm (about 1 in) long. When fully fed, they go into the soil to pupate.

The large rose sawfly (Arge pagana) will produce two (sometimes three) generations from May to October. Arge ochropus usually has a single generation in early summer, but sometimes there is a second generation in late summer.

A guide to distinguish the adults and larvae of the two species of large rose sawflies can be found on the Sawflies of Britain and Ireland website, under information on Arge ochropus. One simple way to determine the species is that the eggs of A. ochrops are laid in a single row in the twig scar, A. pagana lays eggs in a double row.