Oligonephria: applied to insects with few urinary (Malpighian) tubes.
Oligoneura: having few wing veins: specifically applied in Diptera to Cecidomyids.
Olivaceous: with a tinge of olive-green, usually as a shading [olive green].
Omaloptera: the pupiparous flies.
Omia: the shoulders: the lateral anterior angles of an agglutinated thorax, when they are distinct:= see umbone: in Coleoptera; a corneous sclerite to which the muscles of the anterior coxa are attached; also the lateral margin of the prothorax; also the lateral margin of the scutellum in Carabids and Dytiscids.
Ommateum: the compound eye.
Ommatidium -ia: one of the elements of which the compound eye is composed.
Omnivorous: a general feeder upon animal or vegetable food, or both.
Oncus -i: a welt: applied to welt-like ridges on caterpillars.
Onisciform: shaped like a wood-louse, Oniscus sp.; applied to certain Lycaenid and other caterpillars.