Water mites have a complex life history involving metamorphosis from hexapod larvae that are ectoparasitic on adult insect hosts to octopod nymphs and adults that typically are free living voracious predators of immature aquatic insects and microcrustaceans. Thus, water mites are important in regulating the populations of these invertebrates throughout their lives. Larval water mites parasitize hosts from a number of different insect orders including Diptera, Trichoptera, Plecoptera, Coleoptera, Hemiptera and Odonata. The parasitic relationship provides both nutrition for developing water mite larvae and the primary mechanism for water mite dispersal. Larvae remain attached for a period of feeding after which survival depends on detachment from the host into an aquatic habitat suitable for post larval development. Following detachment, engorged larvae enter a quiescent protonymph stage during which larval tissues are resorbed and the deutonymph develops. Deutonymphs, which resemble adults but are sexually immature, feed and increase substantially in size. When fully grown, they enter a second inactive period, the tritonymph stage, during which anatomical and morphological reorganization occurs to produce the adult. Deutonymphs and adults of many species prey on immature insects belonging to the same taxonomic groups whose adults they parasitize as larvae. Adults are slightly or strongly sexually dimorphic and males produce spermatophores which are transferred to females using pheremonal, behavioral and visual cues, often during elaborate courtship displays.