Size: 877 mm SVL, 1187 mm TL, can reach 1.4 m; hatchlings 250 mm. Dorsal scale rows 17 at mid-body, reduced to 15 posteriorly; each scale has a pair of apical pits, otherwise smooth. Rostral visible from above; nasals divide, nostril large; loreal rectangular; one preocular; two or three postoculars; upper labials 8−10, lower labials 8−10; ventrals 179−196; divided cloacal plate; 106−124 divided subcaudals; eyes large. A lateral stripe on scale rows 4–5. Juveniles are red brown with about 72 white dorsal cross bands, each bordered with black. The colors change to olive green or olive brown with maturity. The combination of 17 rows of dorsal scales with apical pits, a loreal, a vertebral scale row that is not enlarged, and five lower labials in contact with the first chin shield, will separate the species from all other Trinidad and Tobago snakes, except for the two other species of Mastigodryas. The Tobago Racer, M. dunni, is restricted to that island and has an extra stripe on scale rows 1−2. The Yellow-necked Racer may be found (not confirmed) on both Trinidad and Tobago and potentially sharing habitat with this species and M. dunni and it has a stripe on the anterior body that spans scale rows 3−4−5. A common, fast moving, ground dwelling, forest snake often in leaf litter but it will enter grassy areas at forest-edge and ponds. Diurnal. Diet includes insects, frogs, lizards, nestling birds, rodents, and reptile eggs. A study on a Brazilian population found lizards made up 74% of the diet, followed by mammals and frogs; it also reported female’s take a wider range of prey than males, and female feed when carrying eggs. Females deposit eggs in May. Other common names: Boddaert's tropical racer, grass machete, couesse grass snake.