The black rat snake and the black racer are related and do look somewhat alike. They’re both slender and graceful snakes that grow to around the same length -- about 4 feet -- though some individuals have been known to grow longer. They’re both good climbers and can be found in trees and bushes. They have young that are strongly patterned and get darker as they get older. Both are nonvenomous and considered beneficial because they eat vermin.
The black rat snake has keeled scales and some scales tipped with white. It has white on its throat and chin. The black racer is completely black, both above and below. Its scales are smooth and not keeled. Male racers can be distinguished from the females because their tail is longer with a wide base and even a bulge, while the female’s tail tapers from her body. There doesn’t seem to be such sexual dimorphism in the rat snake.
The black rat snake mates in May and lays a dozen or more eggs in July, often in a pile of manure, so the heat from the manure helps incubate the eggs. The young hatch in September and are about a foot long. The racer mates from late April until early June, and in June or early July the female lays three to 32 oval white eggs in a hidden nest, such as a rotted stump or log, old mammal burrow, or a nest cavity. The babies hatch around August or early September and are from 7.5 to 14 inches long. Racers sometimes lay their eggs communally.
The rat snake is beneficial because it eats rats and other small rodents. When young, it eats small lizards, baby mice and small frogs. The rat snake kills its prey by constriction. It grabs the prey and wraps its body around it and squeezes until the prey suffocates. The racer eats small animals, insects, birds, frogs, lizards and other snakes. Even though its Latin name is coluber constrictor, the racer doesn’t constrict its prey, but pins it with its coils or just swallows it alive.
The black racer is ferocious when cornered or molested. Some racers vibrate the tips of their tails among dry leaves so that they sound like a rattlesnake. If they're grabbed by the neck they will thrash around wildly, and if they bite they’ll jerk their head to the side and rip a person's flesh. They’ll also defecate. Black rat snakes tend to be less aggressive in their defense. When approached they’ll freeze. Some might vibrate their tails like the rat snake and then strike when all else fails. Some rat snakes are kept as pets, while racers almost never are.
The black rat snake is found in the United States from New England throughout the south, the Midwest and into Texas, with populations in southern Canada. They like rocky hillsides and flat farmland. Racers have a larger range, though the black racer also can be found in the eastern part of the United States, from Maine to Louisiana.