olm, (Proteus anguinus), blind salamander belonging to the family Proteidae (order Caudata). It lives in the subterranean streams in karst areas of the Adriatic coast from northeastern Italy southward into Montenegro. As an aquatic cave dweller, the olm has lost its skin pigmentation, and its vestigial but light-sensitive eyes are covered with skin. It retains numerous larval traits, such as well-developed gills, a lateral line system, and tiny limbs. The olm grows to about 30 cm (12 inches) long and has a normally white (unpigmented) body, red gill plumes, a narrow head, and a blunt snout.
Olms reproduce by either laying eggs or giving birth to live young. Temperature appears to be the factor that determines which reproductive strategy is used, with colder water triggering the bearing of live young. Adults commonly produce two live larvae using the live-bearing strategy, whereas they may produce up to 70 eggs using the egg-laying strategy.