The effects of feeding by an abundant glossosomatid trichopteran on the density of epilithon on cobbles in an upland stream were evaluated by using both exclosures and flow-through in-stream channels. The in-stream channel experiment found that Agapetus kimminsi Banks had the ability to reduce significantly the density of epilithon on experimental substrata and that this effect was more pronounced on the sides of experimental substrata. The exclosure experiment found that excluding Agapetus monticolus Banks from experimental substrata within the stream had no effect on epilithon density. The different results from the two experiments appear to be due to the use of different experimental protocols and indicate that although Agapetus species are capable of affecting the density of epilithon, they may have only a limited effect within the stream. The limited effect of Agapetus species on the density of epilithon may be due to the effects of other environmental factors (e.g. current) both on the foraging activities of Agapetus species and on the density of epilithon.