any insect of the family Phlebotomidae (sometimes considered part of the family Psychodidae) of the order Diptera. The aquatic larvae live in the intertidal zone of coastal beaches, in mud, or in wet organic debris.

Sand flies are of considerable medical importance: around the Mediterranean and in southern Asia, Phlebotomus transmits the pappataci fever virus; and in parts of South America, Africa, and Asia it carries the protozoan parasites causing kala azar, Oriental sore, espundia, and bartonellosis. The name sand fly is also used for certain species of the black fly and biting midge (qq.v) families.