Iris Sawfly - Rhadinoceraea micans

The adult sawfly is all black and most commonly encountered flying around its host plant, Flag Iris. The larvae feed on this plant but have also been found on other irises.

Very similar to Phymatocera aterrima which feeds on Solomon's Seal. In R. micans the antennae are about twice as long as the width of the head and about as long as the abdomen. In P. aterrima the antennae are at least three times as long as the width of the head and as long as the whole body.

adult, larva - when the host plant is known

For your record to be accepted you should describe how you identified this species.

Adults and larvae can be seen on plants of the Iris family such as Yellow Flag that grow near to water or in damp conditions.

Adult in late spring and summer.

The larvae feed on members of the iris family, but only on plants growing in damp conditions or near to water. They eat strips from the edge of the leaves.

Common and widespread in the southern half of Britain, but there are fewer records further north. 

Status in Leicestershire and Rutland not known due to lack of records.

https://www.sawflies.org.uk/rhadinoceraea-micans/