The male, female, and immature stages of Cosmolaelaps passali n. sp. are described and illustrated. This mite bas been taken only in association with the homed passalus beetle, Popilius disjunctus (Illiger). The female mite is common on the beetle, attaching by the chelicerae to setae just in front of legs I. The male mite is only rarely found on the beetle, and the immature stages have never been taken on the beetle. The immature stages live in frass in and near the beetle tunnels. Records taken for monthly collections over a 20 month period showed that approximately 40 percent of the 999 passalus beetles collected had C. passali mites attached and those beetles with mites averaged 2.88 mites pcr beetle. The fewest mites were found on beetles collected in midsummer and early faU; the most mites were found on beetles taken during the colder months of the year. Statistical treatment of the data showed that the mites were not randomly distributed among the beetles collected.