We here report on the venom composition of Bothrops insularis, an endemic snake from the island of Queimada Grande (São Paulo, Brazil) that shows ontogenetic change on diet. Electrophoretic profiles showed similar patterns among samples at distinct ages. Densitometric analysis showed an increase of expression of proteic band at 24 kDa of molecular mass range. Venom toxicity was higher for bees (just-emerged Apis mellifera) and chicks (one day age Bovans white chicks) than for swiss mice, although a direct relation with ontogeny was not established. Venom selectivity towards local preys was demonstrated by the strong toxicity upon arthropods and chicks in comparison to mammals. Results suggest that the venom of Bothrops insularis has peculiarities on its composition that supports a specialized diet on its insular habitat and, although a conspicuous ontogenetic diet change occurs in the species, venom toxicity towards local preys is a characteristic present during the whole life cycle. Our results also provide strong evidence of the presence of taxon-specific toxicity in the venom of B. insularis, and a tendency of the adult venom to be more toxic than the one from young individuals.