A medium-small species rather resembling C. fodiens in the field. Females have a much darker first tergite without the long hairs and extensive markings of fodiens, and the face is less densely-haired. Marginatus females are smaller and darker-looking with the face even less dense haired than similis.
C. similis is a southern species (extending north to Lancashire), fairly frequent in some districts but decidedly scarce in others. It uses quite a broad range of habitats, including coastal dunes, vegetated shingle, soft-rock cliffs, heathland and chalk grassland. There is a heavy reliance on brownfield sites in some areas (often occurring alongside C. daviesanus).
Pollen is obtained mainly from Asteraceae, though other flowers such as umbellifers are used as nectar sources. Nesting occurs in small aggregations and it does not seem to often attain the abundance of species such as fodiens and daviesanus. Adults fly from June till September.