1. The size of the foraging populations of bumblebee colonies remained fairly constant throughout the day with a peak between 10.00 hrs. and 11.00 hrs. There was a tendency for the proportion of pollen loads to nectar loads collected to increase during the day. About 15% of the foragers of bumblebee colonies spent the night away from their nests. 2. There was a large variation in the number of trips per day made by bumblebee foragers. Foragers which collected pollen spent longer per trip than those which collected nectar only, and spent longer inside their nests between trips.B. lucorum foragers made fewer trips per day and spent more time on each trip than did the other species studied (B. agrorum, B. pratorum andB. sylvarum). 3. The rate at which bumblebees drank sugar syrup depended on the concentration of the syrup and the size of the bee. Larger bumblebees ingested larger volumes than smaller bumblebees, although the latter collected larger loads in proportion to their body size. Individuals varied greatly in the size of pollen loads that they collected.