Climate warming predicted for this century will impact ecosystem processes and food web dynamics across the globe. Litter decomposition in streams is expected to increase with temperature but microbes and invertebrates may respond differently, with implications for brown food webs and element cycling. Recent studies using leaf litter enriched with stable isotopes have challenged traditional views of litter quality, demonstrating that slowly decomposing litter promotes element assimilation by stream invertebrates, but this relationship has not been tested across a temperature gradient. Here, we present results from a unique warming experiment where we traced Q. gambelli and F. velutina litter labeled with 13C and 15N into microbial communities and a shredding caddisfly. We measured microbial biomass, total element assimilation and the percentage of litter C or N lost during decomposition that was incorporated into invertebrate biomass, a measure of trophic efficiency. Three patterns emerged: (1) invertebrate growth and assimilation increased with temperature; (2) trophic efficiency peaked at intermediate temperature on slowly decomposing leaves; (3) microbial biomass was highest on rapidly decomposing F. velutina but microbial standing stocks were invariant with respect to warming. These results indicate that temperature promotes invertebrate breakdown up to a thermal maxima and warming beyond this this threshold results in a decline in efficiency.