A long-standing program in Maine promotes stocking of dragonfly (Odonata) nymphs for biological control of nuisance and vector mosquitoes. Currently the only sources of dragonflies for stocking are out-of-state biological supply companies. In 2 dragonfly shipments from suppliers in Massachusetts and North Carolina, we determined that 6.8% and 38.5% of species, respectively, were not native to Maine. In an experiment of stocking efficacy, we introduced 4, 2, or 0 dragonfly nymphs into artificial pools in a forest habitat and found no differences in mosquito larvae counts among treatments. While the motivation for using dragonflies as biological control agents is commendable, the practice may be ineffective, and risks accidental introductions of non-native aquatic plants and animals in water used for shipping.