- Keeled dorsal scales in 19 rows at midbody.
- Undivided anal plate.
- Sharply defined longitudinal stripes: a vertebral stripe and two lateral, light colored stripes placed on the third and fourth scale rows.
Absence of checkerboard blotches seen in many other species of Thamnophis.
Absence of pigmentation outlining white supralabials.
Body shape is particularly slender when compared to other species of Thamnophis.
Elongated tail is much longer than other congeners.
There are four recognized subspecies of T. proximus found in Texas, all of whose definitions differ in the coloration of their stripes as well as their background color. Adding to the confusion, these four subspecies all readily interbreed, and consequently distinct boundaries for the ranges of the subspecies are impossible to define with intergradation seen between all four taxa.
Thamnophis proximus is one of the largest gartersnakes in Texas with adults measuring between 51-76 cm (20-30 in) in length, with exceptional individuals measuring over 91.5 cm (36 in).
Thamnophis proximus is seen throughout many of the south central United States, and ranges well through Mexico, along the Atlantic versant, reaching as far south as Costa Rica.
Foods consumed by ribbonsnakes are primarily amphibians, with tadpoles eaten when available and frogs and toads taken year round. Fish and lizards are also known as potential prey items. Active at dusk and dawn during the spring and fall seasons, T. proximus is can be entirely nocturnal in hot habitats during the summer months. Although it is listed as a non-venomous snake, the saliva of T. proximus has been reported to have toxic properties, though few human envenomations have been reported. It is not thought to be dangerous to humans, and will not bite unless provoked.
Thamnophis proximus is viviparous, as are all Thamnophis, giving birth to live young in July and August. Litter sizes can be as great as 25 snakes, with each neonate measuring between 23-30.5 cm (9-12 in).
The range of the four subspecies of Thamnophis proximus is widespread over Texas. Ribbonsnakes are found in a wide variety of habitats including Chihuahuan desert, coastal marshes, south Texas thornscrub, and north Texas woodlands. The unifying factor of all these habitats is the nearby availability of water, whether in the form of ponds, streams, or swamps
The ribbonsnake is not a protected species in Texas and can be legally collected with a hunting license.
The range of the four subspecies of Thamnophis proximus covers the majority of Texas, only being absent from portions of the western Trans-Pecos and Panhandle.