Bee lice were found in 28% of Maryland apiaries and 18% of the colonies examined. In apiaries with lice, 50% of the colonies contained lice. Laboratory tests demonstrated that bee lice had no preference between 1, 5, 15, and 30 day old honey bee (Apis mellifera L.) workers at 25° while there was a preference for 1 day old workers at 34° C. Lice preferred young drones over old drones and virgin and mated queens over young drones at 25 and 34° C. Lice preferred virgin queens over old drones at 25° C while no preference was observed at 24° C. Mated queens were preferred over old drones at 25 and 34° C. There was a preference of lice for foraging age workers over old drones at 25° C while there was no preference at 34° C. Lice preferred both virgin and mated queens over random age workers at 25 and 34° C. Louse larval tunnels were numerous in nucs (4 frame honey bee colonies) stocked with lice from May through August corresponding with periods of nectar flow when bees were capping honey. In field colonies, louse populations decreased in the late spring to a low in early June. During July and after, populations of lice rose with the emergence of new lice. Few immature and adult lice were observed in control nucs having similar populations of bees. In nucs, 1 or more lice were observed on 24% of the queens between August and December. Only 2% of the virgin queens contained lice during the same period. In field colonies, 62% of the queens examined from June through the rest of the season harbored lice; 58% of these lice were pale in color indicating they were less than 1 day old. One louse was observed on 98.6% of the workers with lice, while 1.2% harbored 2 lice and 0.2% had 3 lice; 4 .2% of the lice were on drones. A single bee louse was observed on 3,092 foraging honey bees sampled. One-hundred-seventeen lice were collected on 14,459 bees collected from the brood nest of the same hives. Control samples indicated a 14 to 15% loss of lice during sampling. Tests demonstrated that during visual observations of lice on bees only 49% of the lice present were observed. Fluctuation in louse population levels were similar to those found elsewhere in this study.