The larvae of the Iris Sawfly defoliate iris plants growing near ponds, lakes or canals, but do not attack irises that grow in dry soils.
Initially they eat Vee-shaped notches in the leaf margins, then continue eating into the leaf until most of the upper leaf blade is eaten down to the central vein.
Luckily most plants that become defoliated by this action generally survive!
The adult sawfly has a black body with two pairs of dark grey wings, the female of which lays its eggs on iris leaves in late April-May.
The caterpillar like larvae emerge in June-July and grow to approximately 25mm (1”) long, when fully fed they burrow into the soil to pupate till the following spring.
Young sawfly larvae are susceptible to insecticides, however, these might also affect other wildlife in or around the pond e.g. fish and frogs.
The safest control is to remove the larvae by hand.