Solomon's Seal Sawfly Larvae

There is a small patch of Solomon's Seal in the garden and yesterday I noticed that some of the leaves had been stripped bare. I thought it was possibly slug or snail damage. However, today I noticed some unpleasant looking grey caterpillars on some of the remaining leaves. The internet soon provided the answer. They are not true caterpillars but the larvae of the Solomon's Seal Sawfly (Phymatocera aterrima).

Adult Solomon’s Seal Sawfly are black, 8-9mm long, and emerge in late spring at about the time the host plant is coming into flower. The female uses her saw-like ovipositor to insert rows of eggs into the leaf stems. The larvae initially make small elongate holes in the foliage (as in above photo), but as they increase in size their appetite also increases. The fully grown larvae go into the soil where they overwinter and pupate in the following spring. Defoliated plants survive but may produce reduced growth in the following year.