A key aspect of modeling contaminant uptake by animals is knowledge of the route taken by the contaminant to enter the animal. To determine the relative importance of food and water as Cd sources for benthic insects, we measured Cd accumulation by the predatory alderfly Sialis velata (Megaloptera) from either water alone or from chironomid prey (Cryptochironomus sp.). We determined that Cd uptake from prey was far more important than that from water. Chironomid prey fed to S. velata also appeared to take up the bulk of their Cd from food (meiobenthic organisms). The efficiency with which Cd was assimilated by the predator from its prey is high (50%) and comparable with values reported for several other insects. In the predator, Cd taken up from food was largely stored in gut tissues (as is the case for insect larvae in nature), whereas a greater proportion of the metal taken up from water was stored in other animal parts.