The megalopal stage ( = postlarva) of the blue crab Callinectes sapidus Rathbun enters Chesapeake Bay after larval development in coastal waters and settles in shallow areas of lower Chesapeake Bay. We examined the effects of two potential predators, two megalopal densities and two levels of habitat complexity on mortality of blue crab megalopae in laboratory experiments. Sand shrimp Crangon septemspinosa Say consumed > 99% of megalopae in each of two 40-h trials. Grass shrimp Palaemonetes pugio Holthuis consumed 37% of megalopae in the first trial, but only 5% in the second trial. No effect of habitat (sand or sand with artificial seagrass) or prey density on predation rates for either predator species was found. We then tested the hypothesis that megalopae undergoing metamorphosis to the first juvenile instar suffer higher mortality to grass shrimp predation than megalopae not in the process of metamorphosis. This hypothesis was rejected because predation rates did not differ between treatments with 0 or 95% metamorphosis. Higher predation rates (77.4%) by grass shrimp in the second set of experiments were associated with warmer water temperature, though temperature was not included formally as a factor in the design. These shrimps are seasonally abundant in Chesapeake Bay grass beds and capable predators of blue crab megalopae in the laboratory; field studies will be necessary to determine their impact on blue crab recruitment success.