Breeding sites of phlebotomine sandflies at the bases of trees in Panama were studied by systematic soil sampling and analysis, rain-gauge experiments, topographic mapping, and rearing of field-collected larvae in the laboratory. It was found that the sandfly species complement of this breeding habitat is specialized, dominated byBrumptomyia hamata(Fairchild&Hertig). The species complement is of potential medical importance because of inclusion ofLutzomyia ovallesi(Ortiz). The principal environmental factor affecting sandfly populations and species compositions in the tree-base habitat is that of protection from flooding from rainfall or soil run-off.