The ecology of two species of tree-climbing crabs, Malagasya antongilensis (Rathbun, 1905) (Potamonautidae) and Labuanium gracilipes (H. Milne Edwards, 1853) (Sesarmidae), collected from container microhabitats (phytotelmata) in rainforest in the Masoala Peninsula, Madagascar, is described. This is a rare report of a tree-climbing phytotelmic sesarmid crab living in the rainforest canopy, and the first record of a species of true freshwater crab in the canopy, albeit at a relatively low height. The difficult-to-access rainforest canopy surveys were made as part of the Canopy Raft Program (Radeau des Cimes). The occurrence of crabs in water-filled plant containers in rainforest habitats is discussed.