A purebred "spotless" line of Nicrophorus orbicollis was produced by inbreeding. Spotless beetles completely lack orange markings on the basal portion of the elytra. The spotless trait appears to be largely under the influence of a single gene and is an excellent genetic marker for paternity or maternity in a variety of competitive breeding situations. In the laboratory, individuals possessing the spotless trait were as reproductively successful as normally marked beetles. The spotless marker was used to demonstrate that males which pair with a female achieve a high level of paternity. Paternity remained high in a second brood even when the male was separated from the female in the interval between reproductive attempts.