They are black , with longitudinal grooves on the surface of the elytra .
The adults grow up to 7 -- 12 millimetres ( 0.28 -- 0.47 in ) long .
adults are black , with longitudinal grooves on the surface of the elytra .
The adults grow up to 7 -- 12 millimetres ( 0.28 -- 0.47 in ) long .