The immature stages are known for very few Trigynaspida (Mesostigmata) mites. Biological information for these mites is generally limited to associations based on collection records of the adults. For the past two years, we have been conducting biological studies with the Trigynaspida mite, Euzercon latus (Banks) (Euzerconidae). The present paper, one of a series on the Mesostigmatic mites associated with the horned passalus beetle, Popilius disjunctus (Illiger), gives descriptions and illustrations of the life stages, seasonal abundance and other observations on the biology of E. latus.