Nicrophorus beetles reproduce by burying small vertebrate carcasses underground in a brood chamber. All stages of the phoretic mite Poecilochirus (Mesostigmata: Parasitidae) associate closely with Nicrophorus beetles by clinging to them for transportation and by reproducing in the beetles’ brood chamber. Presumably, the fitness of phoretic mites is affected by the ability of their beetle host to successfully locate and bury a carcass. Previous studies have shown that thermoregulation during flight, competitive ability, burying speed, and burial depth are all positively correlated with adult beetle body size. This study, conducted in the Rocky Mountains of southwestern Colorado, addresses whether deuteronymph mites discriminate among male Nicrophorus investigator Zetterstedt (Coleoptera: Silphidae) hosts based on beetle body size, a proxy for beetle condition. We found that the number of phoretic mites on wild-caught male N. investigator beetles was positively correlated with beetle body weight and other measures of adult beetle body size. Laboratory trials with pairs of N. investigator beetles also demonstrated that deuteronymph mites preferentially associate with larger beetle hosts. A test to determine whether mites select hosts based on nutritional status was inconclusive. These results suggest that deuteronymph mites discriminate among adult male Nicrophorus based on body size, which is consistent with a choice that would benefit the mite. The precise mechanism by which mites detect size is not known, but it is most likely chemical.