Plant-pollinator interactions are based on mutual benefits; the plant gains fertilization and the pollinator gains food resources. But aside from providing rewards, flowers can be risky places to visit, for example if a predator ambushes during the feeding/pollination process. Here, we show that pollination may also involve the transmission of pathogens for the pollinators. Experimental evidence is given that a trypanosome parasite, Crithidia bombi, can be horizontally transmitted within populations of its hosts, the bumblebees Bombus spp., through the shared use of flowers. Important floral characteristics such as nectar availability or inflorescence architecture may also affect transmission rate. Therefore, in addition to energetic considerations, pollinator strategies could also be governed by the risk of contracting pathogens.