South American Yellow-bellied Racer
Mastigodryas bifossatus • Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Colubrinae, Genus: Mastigodryas, Species: Mastigodryas bifossatus
Widely distributed across South America, including Brazil, Argentina, Paraguay, Uruguay, Bolivia, and parts of Colombia and Venezuela.
Look up South American Yellow-bellied Racer in the Snake Encyclopedia →Venomous Status
Non-venomous (aglyphous dentition)
Danger Level
Harmless; while large specimens may bite defensively if cornered or handled, they possess no venom and present minimal risk to humans.
Family
Order: Squamata, Suborder: Serpentes, Family: Colubridae, Subfamily: Colubrinae, Genus: Mastigodryas, Species: Mastigodryas bifossatus
Conservation
Least Concern (IUCN). It is a highly adaptable species that thrives in human-modified landscapes, though it faces local threats from habitat loss and intentional killing due to fear.
Physical Description
Large, slender-bodied snake with smooth scales. Coloration is typically greyish, tan, or brown with a series of large, dark, rectangular or saddle-like blotches along the back. The head is distinct from the neck with large eyes and round pupils. The ventral surface is usually yellowish (giving it its common name).
Size & Dimensions
The specimen in the image appears to be an adult. Typical size ranges from 120 to 180 cm (approx. 4 to 6 feet), though specimens can occasionally exceed 2 meters.
Habitat
Terrestrial and semi-arboreal, typically found in open areas such as savannas (Cerrado), Pantanal wetlands, pastures, forest edges, and disturbed areas near human habitation.
Behavior & Temperament
Highly active and diurnal; known for being extremely fast and alert. When threatened, they often raise the front part of their body off the ground (periscoping, as seen in the image) and may vibrate their tail or strike if further provoked.
Diet & Feeding
Generalist predator. Primarily feeds on frogs, lizards, and small mammals. They are active hunters that use speed to overtake prey and swallow it alive or with mild constriction.
Reproduction
Oviparous (egg-laying). Females lay clutches typically ranging from 8 to 20 eggs depending on the size of the individual; breeding usually coincides with the rainy season.
Venom Profile
Non-venomous - no medically significant venom.
Look-alikes
Often confused with Pit Vipers (Bothrops species) due to its blotched pattern (mimicry). It can be distinguished from vipers by its slender body, round pupils, absence of heat-sensing pits, and extremely fast movement.
Conservation Status
Least Concern (IUCN). It is a highly adaptable species that thrives in human-modified landscapes, though it faces local threats from habitat loss and intentional killing due to fear.
Cultural Significance
Commonly encountered in agricultural areas where it is ecologically beneficial as a natural pest control agent, significantly reducing rodent and pest populations.
Notable Features
It is famous for the behavior shown in the image: 'periscoping,' where it lifts its head high above the grass to survey its surroundings for prey or predators.