Bdelloid rotifers are basal consumers in aquatic and limnoterrestrial communities that feed primarily on small bacteria. Unfortunately, we know only a little of the role they play in the trophic dynamics in some unusual habitats they inhabit. Habrotrocha thienemanni is a typical example; it is a typical tree-hole inhabitant, commonly achieving dense populations. Filtering rates of H. thienemanni were estimated using fluorescent microspheres of a size close to natural bacterial community (0.5 mu m in diameter) at two temperatures (15 and 20A degrees C). This microspheres artificial food had been coated with BSA protein. Mean clearance rates of this rotifer varied between 1.65 and 3.79 mu l ind(-1) h(-1) under different temperatures. Uptake of particles coated with protein was significantly higher than that on uncoated particles (t = 2.85; P = 0.005). Particle uptake also was correlated to the body size of the animal (r = 0.44; P = 0.004,). The clearance rate of the natural H. thienemanni population (56,800 ind l(-1)) ranged from 981 to 5170 ml l(-1) d(-1).