We report on the behaviour of Eupemphix nattereri in Brazil. Reproduction started with the beginning of the rains and, in peak season, could extend into the diurnal period. Pairs built either isolated or communal foam nests close to, but isolated from, water. The density of nests on steep ground was greater than on flatter terrain. After 40 h, nests collapsed and formed a mucus string allowing early tadpoles to enter the water. Infestation of nests by flies was delayed in relation to the beginning of the reproductive season. Tadpoles of two Leptodactylus species preyed upon eggs or tadpoles leaving the foam of E. nattereri; adults were preyed on by water bugs, raccoons and two bird species. Amplectant pairs took refuge under communal nests when approached. Terrestrial nesting appears to be a response to loss of eggs/early tadpoles to aquatic predators. Communal nesting is facultative behaviour and appears to result unintentionally from (1) the massive aggregation of adults, (2) the selection of steep/bare ground to anchor nests, and (3) disturbed couples restarting egg-laying beside previously built nests.
