Male Lepidoptera commonly visit stands of water to drink, a behavior known as puddling. Males of the notodontid moth Gluphisia septentrionis routinely puddle for hours, imbibing hundreds of gut-loads and voiding the fluid as repetitive anal jets. Cationic analyses showed puddling to lead to systemic sodium gain, a potential benefit to Gluphisia, whose larval food plant is low in sodium. Male Gluphisia are specialized for puddling, possessing a wide oral slit and a highly expanded enteric surface. The acquired sodium is transferred to the female at mating, for eventual incorporation into the eggs. Sodium acquisition may be the primary function of puddling in Lepidoptera.