Net-spinning caddisflies (Trichoptera: Hydropsychidae) are widely distributed and locally abundant ecosystem engineers. Their silk nets and retreats aggregate resources, create hotspots of ecosystem function, and support higher densities of other macroinvertebrate taxa than adjacent habitats. To assess the strength of caddisfly facilitation across a range of population densities, we stocked 15 in-stream mesocosms with natural macroinvertebrate assemblages and varying numbers of the net-spinner Arctopsyche grandis. After 3 weeks, macroinvertebrates from the mesocosms showed little evidence that high densities of A. grandis contributed to an increase or decrease in the abundance of several key taxa. However, further examination revealed that A. grandis frequently preyed upon other macroinvertebrates. Taxa which were often facilitated by different net-spinner species (i.e., Hydropsyche spp.) in previous research, including chironomid larvae, were among those consumed by A grandis. This result may indicate that the overall outcome of interactions between ecosystem engineers and associated beneficiary taxa is dependent on tradeoffs between the positive effects of ecosystem engineering, the risk of predation by the same engineer, and instar stage. Using A. grandis as a model species, we explore a conceptual framework for predicting the influence of predatory ecosystem engineers on freshwater communities.