Phoretic females of Scutacarus acarorum Goeze occur in Denmark on bumblebees (Bombus Latr.) and cuckoo bumblebees (Psithyrus Lep.). Frequency and number of S. acarorum on castes of Bombus terrestris L. and B. lucorum L. is recorded; the mites occur primarily on queens. Greatest number - 115 - was found on an overwintered queen of B. terrestris. Small numbers could be found on deutonymphs of Parasitus species (Mesostigmata) phoretic on the bumblebees. Physogastric females were found on bumblebee workers and drones and in late spring on queens. S. acarorum was reared in mass cultures feeding on mycelium of Histoplasma capsulatum Darling. Morphology of the S. acarorum male is illustrated.