The present study ofLeptanilla japonica has clarified for the first time the biology of the Leptanillinae. Males were obtained, which are the first specimens of the subfamily to be collected in association with workers.L. japonica is a totally subterranean ant. Colonies are monogynous with a dichthadiiform queen. Worker population per colony is small, usually 100–200. Development of immature individuals is strictly seasonally synchronized. Colonies often emigrate to the site of paralyzed prey (geophilomorph centipedes). For carrying larvae workers grasp peculiar structures projecting from the larval prothorax with the lower mouthparts. The final-instar larvae have a pair of specialized lateral duct organs on the 4th abdominal segment. Through these organs larval hemolymph is provided for consumption by adults, especially by the queen. Nutrition of the queen depends exclusively on this process. The frequency of larval hemolymph feeding by queens is abruptly elevated when the larvae mature. Owing to this the queen is able quickly to achieve full physogastry, and to lay a batch of 100–200 eggs within a few days. Emergence of new workers from pupae is synchronized with hatching of the 1st-instar larvae from the eggs. In a concluding section the lifemode ofLeptanilla is compared with that of doryline and ecitonine army ants