Nerodia rhombifer, commonly known as the diamondback water snake, is a species of nonvenomous natricine colubrid endemic to the central United States and northern Mexico. There are three recognized subspecies of N. rhombifer, including the nominotypical subspecies. Taxonomy and systematics The species was first described as Tropidonotus rhombifer by Edward Hallowell in 1852. Description The diamondback water snake is predominantly brown, dark brown, or dark olive green in color, with a black net-like pattern along the back, with each spot being vaguely diamond-shaped. Dark vertical bars and lighter coloring are often present down the sides of the snake. In typical counter-colored fashion, the underside is generally a yellow or lighter brown color, often with black blotching. The dorsal scales are heavily keeled, giving the snake a rough texture. The dorsal scales are arranged in 25 or 27 rows at midbody. There are usually 3 postoculars. Adult males have multiple papillae (tubercles) on the under surface of the chin, which are not found on any other species of snake in the United States. Nerodia rhombifer grows to an average total length (including tail) of . The record total length is . Neonates are often lighter in color, making their patterns more pronounced, and they darken with age. Habitat The diamondback water snake is one of the most common species of snake within its range. It is found predominantly near slow-moving bodies of water such as streams, rivers, ponds, or swamps. Behavior When foraging for food the diamondback water snake will hang on branches suspended over the water, dipping its head under the surface of the water, until it encounters a fish or other prey. It is frequently found basking on branches over water, and when approached, it will quickly drop into the water and swim away. If cornered, it will often hiss, and flatten the head and body to appear larger. It only typically resorts to biting if physically harassed or handled. Its bite is known to be quite painful due to its sharp teeth meant to keep hold of slippery fish. This defensive behavior is frequently misinterpreted as aggression and often leads to its being mistaken for the venomous cottonmouth (Agkistrodon piscivorus), with which it does share habitat in some places. The brown/tan coloration and diamond-shaped pattern also causes it to be mistaken for rattlesnakes, especially when encountered on land by individuals unfamiliar with snakes. Geographic range The diamondback water