Quite a large sawfly (to15 mm or more). The pronotum is entirely black except the yellow apical border. –The face is also generally black though may have minor yellow spotting. The long, slender black abdomen is striped with whitish or pale yellow bands and the wing has a long brown shaded stigma. The tibia and tarsi of the legs are yellow.

Phylloecus species look similar to Calameuta. There are three British Phylloecus species:

P. nigra lacks any yellow on the pronotum.

P. linearis has a yellow face.

Flower rich areas, particularly areas where Meadowsweet is found.

Summer.

Larvae feed within the stems of Meadowsweet.

Scarce with fewer than 50 records on NBN by mid 2014.

Phylloecus species look similar to Calameuta. There are three British Phylloecus species:

P. nigra lacks any yellow on the pronotum.

P. linearis has a yellow face.

https://www.sawflies.org.uk/phylloecus-xanthostoma/