If selective forces on locomotor ability and reproductive biology differ among habitats, we expect to see relationships between habitat, morphology, and life‐history traits. Comparative (phylogenetically based) analysis of data from 12 pythonid and 12 boid snake species reveals multiple evolutionary shifts in habitat use, notably in the evolution of arboreal habits. Compared to terrestrial and aquatic taxa of the same overall body size, arboreal species have narrower and more laterally compressed bodies and relatively longer tails. Offspring sizes are not affected by arboreality, but presumably reflecting space constraints within their narrow bodies, arboreal species (1) produce smaller clutch sizes relative to maternal body length and (2) have left and right ovaries that overlap little if at all along the length of the body (i.e., the right ovary is positioned anterior to the left ovary) whereas in terrestrial snakes the two ovaries overlap along much of their length. This modification of ovarian morphology in arboreal snakes presumably reduces the degree of bodily distension during vitellogenesis and pregnancy, thus enhancing climbing ability and camouflage among the branches.

One hundred and seventy‐three adults and twenty‐six juveniles of Crotalus durissus were examined by removing the stomach contents and faecal material. Rattlesnakes were most active between April and May (autumn) (unimodal type), but most intensive feeding occurred during summer and autumn (February to May). Juveniles were observed to feed from late autumn (May) through the winter. Prey consisted of rodents (Cavia aperea, Rattus norvegicus and Mus sp.) and no ontogenetic change was observed in the diet. Feeding peaks precede vitellogenesis (autumn ‐ winter). Mated females continue feeding until ovulation (spring). It was observed that the biggest number of accidents were caused by snakes with stomach contents, especially males.