P.  Yeo and Corbet, S. A., Solitary Wasps, 2ndnd ed. 1995, p. 68.

S.  Harris, Morris, P., Wray, S., and Yalden, D. W., A Review of British Mammals: Population Estimates and Conservation Status of British Mammals Other than Cetaceans. Peterborough: Joint Nature Conservation Committee, 1995, p. 216.