What Do Water Snakes Eat? Fish, Frogs and Hunting Tactics

What do water snakes eat?

The best-studied species, the northern water snake, is a generalist that eats almost any small animal it can catch in or near water. Fish and amphibians make up the bulk of its diet everywhere, but the exact mix depends on what is common in each pond, river or marsh.

Most fish they catch are small, slow-moving bottom dwellers or fish that gather in shallow water, such as minnows and young sunfish. Fast, open-water fish are harder for a snake to catch.

How do water snakes hunt?

Water snakes use several hunting styles, and the same snake may switch between them in a single outing.

• Active searching: the snake crawls and swims slowly along the bank, poking its head among plants, roots and stones and into crevices. It uses its eyes and its flicking tongue, which collects scent particles from the water and air.
• Open-mouth sweeps: in shallow water, a water snake may swim forward with its mouth open, sweeping its head from side to side through a school of small fish or tadpoles. When its jaws touch a prey animal, they snap shut. This works even in murky water or in the dark.
• Waiting in ambush: a snake may lie still in shallow water or among water plants and strike when a fish or frog comes close.
• Using the shallows: small fish and tadpoles often crowd into shallow edges, where they are easier to trap. Some observers have described water snakes driving schools of small fish into shallow corners before feeding.

Once it has caught something, the snake does not wrap it in coils. It simply works its jaws forward and swallows the prey alive, usually headfirst so that fins and legs fold back neatly. A large fish may be dragged onto a log or the bank to be swallowed. Snakes can manage prey wider than their own heads because their jaws are joined by stretchy ligaments; see how snakes swallow large prey.

When do water snakes feed?

Northern water snakes can hunt at any time of day. In spring and fall they are mainly active in daylight, basking between hunting trips. In hot summer weather many switch to hunting at dusk and at night, when they pick off minnows and other small fish resting in shallow water.

As cold-blooded reptiles, water snakes depend on warmth to digest. After a big meal they often bask to raise their body temperature and speed up digestion. In the north they stop eating altogether in fall and spend the winter dormant, from about October to April, living on stored fat.

How big a meal can a water snake swallow?

The size of prey grows with the size of the snake. Newborn water snakes, only 19–27 cm (7.5–11 in) long, take small minnows, tadpoles and tiny frogs. Big adult females, which can be well over 1 m (3.3 ft) long and two to three times heavier than males, are able to tackle large frogs and fish as long as a hand.

Because a water snake can survive a long time on a single big meal, it does not need to eat every day. Its feeding rate depends heavily on water temperature, prey numbers and, in females, the demands of carrying young.

Do different water snakes eat different food?

All Nerodia species eat fish and amphibians, but each has its own leanings:

• Lake Erie water snake: on the islands of western Lake Erie, this subspecies of the northern water snake now feeds mostly on the round goby, an invasive fish from Europe and Asia that arrived in the 1990s. Gobies can make up as much as 90% of its diet, and the extra food is thought to have helped this once-threatened snake recover.
• Plain-bellied water snake: often wanders away from water and eats frogs and toads more than most relatives.
• Brown water snake: a large southeastern species that feeds mainly on fish.
• Diamondback water snake: eats mostly fish, plus frogs, in slow rivers, swamps and ponds.

In Europe, the closest equivalents show the same split. The grass snake eats mostly frogs, toads and newts, while the dice snake is a fish specialist that dives for its prey.

Do water snakes harm fish populations?

Many anglers see water snakes as competitors, but studies of their diet tell a calmer story. Water snakes mostly catch small, slow or very abundant fish, along with sick and dying ones, and they eat many frogs and tadpoles too. There is little evidence that they reduce sport fish populations in natural lakes and streams. In crowded ponds, removing some small fish may even help the rest grow larger.

Water snakes are also food for many other animals, including herons, hawks, raccoons, otters, snapping turtles and large bass, which eat young snakes. They are a normal link in the food web of healthy wetlands. Fish hatcheries and fish farms, where fish are packed into shallow ponds, are the main places where they can take a noticeable share.

Is a snake eating fish always a water snake?

Not always. Several other snakes also hunt fish and frogs, including gartersnakes, ribbonsnakes and, in the Southeast, the venomous cottonmouth. Behavior and range are the first clues, but a fishing snake should always be watched from a safe distance. To learn whether these snakes are a danger, read Are water snakes venomous?.