Secondary consumers are organisms that feed on primary consumers. Dragonfly nymphs and mayfly nymphs are both aquatic insects that feed on smaller organisms like zooplankton, protozoans, and other small invertebrates. These smaller organisms are primary consumers, as they feed on producers (algae and other plants). Dragonfly nymphs and mayfly nymphs, in turn, are preyed upon by larger organisms, such as fish and birds, which are tertiary consumers.