Length 4 to 5 mm.   Cymus species have a narrow shape and densely punctured head, pronotum, scutellum and forewings.   Cymus glandicolor is slightly larger than the two other common species, and has a pale keel on the scutellum and a dark streak on each forewing along the cubital vein. 

Cymus aurescens is similar, but much less common; see link below to British Bugs website. It has not been recorded in VC55.

• Pale keel on scutellum
• Two dark streaks, roughly parallel to forewing edge, along cubital veins.

Good photographs taken in the field or of a specimen, clearly showing keeled scutellum

Damp grassland and marsh, associated with sedges and rushes.

Adult: All year

Common (ref.: British Heteroptera checklist 2021 on British Bugs website) 

Occasionally recorded

https://www.britishbugs.org.uk/heteroptera/Lygaeidae/cymus_glandicolor.html