Spilotes sulphureus (formerly classified as Pseustes sulphureus) is one of the largest species of neotropical colubrid snake, and among the largest colubrid species in the world, with adults routinely attaining (and reportedly exceeding) ten feet in length. Common names for the species include the Yellow-bellied puffing snake (or simply, puffing snake) and the Giant bird snake, among a myriad of regional monikers. Close relatives of the species include at least one other species in the Spilotes genus, in addition to the neotropical bird snakes of the genus Phrynonax (also formerly classified as Pseustes).

   An incredibly variable species in terms of morphology, adult sulphureus can display a wide range of pattern and coloration, expressing a broad array of yellows, greens, reds, browns, and black, or any mixture of these colors. Despite this polymorphism as adults, neonates are almost invariably born patterned in black and gray, or varying shades of brown (presumably affording better camouflage from predators) before gradually assuming an ontogenetic shift into their permanent adult coloration. Lean and powerful snakes, their dorsal scales are
large and heavily keeled, and their bodies are laterally compressed granting them an aided capacity to thrust over long distances - a physiological trait which suggests their semi-arboreal habits. Similarly, their large eyes suggest a keen attention to movement, which they put to good use in pursuing highly mobile prey in the thick vegetation of their native environments. Specimens are known to commonly practice liana mimicry, a form of crypsis, if spotted or approached. When threatened, they are known to rattle their tails and inflate their fore-bodies, especially their throats, exposing the interstitial skin between their scales (which is commonly bright yellow). If these measures fail to dissuade their would-be-antagonist, and retreat is not a viable option, they will not hesitate to defend themselves by bluff striking or biting as a last resort. All of these characteristics and more contribute to making sulphureus an especially charismatic and impressive species.

   A wide-ranging snake, sulphureus is found throughout the Amazonian region of South America, from Venezuela and Colombia in the north, the eastern slope of Ecuador in the west all the way to the Atlantic slope of Brazil in the east, and south to Bolivia, as well as the islands of Trinidad and Tobago. Though primarily associated with lowland primary rainforest, they are also reported to occur in savannah, dry forest, and disturbed habitats, possessing both terrestrial and arboreal habits, with wild specimens commonly observed both on the forest floor and within trees. 

   Despite their extensive range and impressive appearance, the natural history of sulphureus is poorly documented, and I’ve been unable to find much literature expressly concerning the species. The image I can deduce of their habits is largely drawn from anecdotal accounts, and only from firsthand experience observing them within captivity, which is to admit it is limited at best. That said, there are some clear consistencies to be seen in the scant observations I’ve excavated and in the experiences of those who have worked with the species in captivity. For one, all accounts confirm that the species is chiefly diurnal and most active during peak daylight hours. They are alert creatures and display a level of attention that is widely characterized as an intelligence uncommon to the majority of snakes. As predators, they are opportunistic and have been recorded to consume small mammals, birds (especially nestlings and eggs), and occasionally amphibians and reptiles. An oviparous (egg-laying) species, breeding behavior in sulphureus is thought to peak during the onset of the wet season, timing which assures ideal environmental conditions for incubation and abundant prey for neonates after emerging from their eggs.

   Though widely classified as non-venomous, recent studies confirm that sulphureus is rear fanged with a venom containing two separate toxins: sulmotoxin, lethal to small mammals but not birds or reptiles, and sulditoxin, lethal to birds and reptiles but not mammals. To summarize broadly, these findings suggest that sulphureus initially evolved with a diet primarily focused on birds and reptiles, and later developed a secondary venom compound to assist in immobilizing rodents, which generally demonstrate a higher value as a food source. Despite this recent development, they are not considered dangerous to humans and no known serious envenomations or fatalities have resulted from their bite, likely due in part to a relatively unsophisticated venom delivery system and a general reluctance on their part to deliver prolonged bites.