The Diamondback water snake (Nerodia rhombifer) is a species of nonvenomous colubrid native to North America. It was first described as Tropidonotus rhombifer by Edward Hallowell in 1852.
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. Neonates are often lighter in color, making their patterns more pronounced, and they darken with age.
Diamondback water snakes are found in the central United States, predominantly along the Mississippi River valley, but their range extends beyond that. They range within the states of Texas, Oklahoma, Kansas, Iowa, Louisiana, Arkansas, Missouri, Illinois, Indiana, Tennessee, Mississippi, Georgia, and Alabama. They are also found in northern Mexico, in the states of Coahuila, Nuevo León, Tamaulipas, and Veracruz. Diamondback water snakes live predominantly near slow-moving bodies of water such as streams, rivers, lakes, ponds, marshes, canals, or swamps.
These semi-aquatic snakes are generally solitary creatures; they spend most of their life alone and only during hibernation, they may share dens with other snakes. Diamondback water snakes are diurnal hunters. When foraging for food they will hang on branches suspended over the water, dipping their head under the surface of the water, until they encounter a fish or other prey. These snakes are frequently found basking on branches over water, and when approached, they will quickly drop into the water and swim away. If cornered, they will often hiss, and flatten the head and body to appear larger. They only typically resort to biting if physically harassed or handled. The bite of these snakes is known to be quite painful due to their sharp teeth meant to keep hold of slippery fish. Unfortunately, this defensive behavior is frequently misinterpreted as aggression and often leads to Diamondback water snakes being mistaken for the venomous cottonmouth, with which they do share a habitat in some places.
Diamondback water snakes are carnivores (piscivores). They feed on a variety of aquatic species such as fish (both dead or alive), frogs, toads, salamanders, crayfish, and minnows. They may also hunt young turtles.
Diamondback water snakes are ovoviviparous which means that they give birth to live young. Adults breed in the spring, and gravid (pregnant) females give birth to 13-62 young in the late summer or early fall. Neonates (snakelets) are born around 8-10 in (20-25 cm) in length. They don't receive parental care and can take care of themselves on their own. Baby water snakes grow quite quickly and reach reproductive maturity when they are 2 years old.
Diamondback water snakes don't face any significant threats. However, in some areas of their range, they do suffer from the destruction and degradation of the aquatic habitat and human ignorance. These snakes are often mistaken for the cottonmouth or rattlesnakes and are killed out of fear. In actuality, Diamondback water snakes and other species of water snakes are far more common than the venomous snakes in their range, especially in areas that are frequented by humans.
According to IUCN, the Diamondback water snake is locally common and widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
Diamondback water snakes control populations of aquatic species they consume and in turn, are important prey for local predators. Newborn baby water snakes are eaten by large frogs and fish, by other snakes, birds, and mammals. Adults are prey for predatory birds and mammals.
