Two species of large black whip snakes (Demansia vestigiata and D. papuensis) are morphologically and ecologically similar and have broadly overlapping distributions. A long history of taxonomic difficulties has meant that most previous taxonomic and ecological studies comprise composite samples of both taxa. Here, we provide ecological data (body sizes, food habits, reproduction and inferred growth rates) collected from captured and road-killed specimens from a tropical population of D. vestigiata at Townsville, north-eastern Queensland, Australia. Males attain larger body sizes and have longer tails than females. All food items were ectotherms (lizards and frogs). Female reproductive cycles were strongly seasonal. Clutch size is significantly positively related to maternal body size. Egg dimensions, clutch mass and neonatal size are reported. Inferred growth rates indicate that sexual maturation is attained at ~21 months for females.