HARLEQUIN-FLY, the popular name of small flies of the genus Chironomus. The larvae, known as bloodworms, are aquatic and live in foul or very deep water where there is little oxygen. To enable them to utilize fully the scant supply of oxygen, these larvae possess in their blood the same red pigment, haemoglobin, that is found in vertebrates. (See DIPTERA; COLOURS OF ANI MALS ; DISTRIBUTION OF ANIMALS. )