The Black Snake Problem

"Black snake" is a description rather than a species, and several unrelated snakes fit it. Most are harmless, and the ones that matter are separable.

Rat snake or racer

The two most likely answers across the eastern United States.

Scale texture. Rat snake scales are weakly keeled — each has a faint ridge down the centre — giving a slightly matte look. Racer scales are smooth and glossy, and a racer in sunlight has an obvious sheen.

Body shape in cross-section. A rat snake's body is squared off where the sides meet the belly, sometimes described as a loaf of bread. A racer is rounded.

Behaviour. Racers are aptly named: fast, nervous, and gone the moment they see you. Rat snakes are slower, will climb readily, and often freeze rather than flee.

Chin. Rat snakes usually have a white or cream chin and throat. Racers have a grey or dark chin, sometimes with a white patch.

Juveniles confuse everyone

Neither is born black. Young rat snakes and racers are both grey with dark blotches, and both are routinely mistaken for copperheads or rattlesnakes because a blotched juvenile matches the mental picture of a venomous snake.

They darken with age, and a metre-long uniformly black snake is an adult of one of these species. A 30-centimetre blotched one may be either, and the copperhead comparison covers the band-shape test that separates the genuinely venomous case.

Water snakes look black when wet

A northern water snake is banded, and a wet adult in poor light looks uniformly dark. Dark adults out of water frequently get called black snakes.

They are harmless, they are frequently killed as cottonmouths, and how they swim is the distinguishing character — covered in cottonmouth or water snake.

The one that matters

A juvenile cottonmouth is dark and venomous, and it is restricted to the southeastern United States. It is patterned rather than uniformly black, and it has a bright yellow tail tip used to lure prey, which no harmless species shares.

Outside that range, a black snake is not a cottonmouth. Check your state is the fastest way to settle whether the species is even present, and it eliminates most of the anxiety this group causes.

What to do

Nothing, in almost every case. Rat snakes in particular are among the most useful animals to have near a house, since rodents are their main prey, and killing one creates a vacancy that gets filled.

If a snake is somewhere it cannot stay, there's a snake in my yard covers moving it on without handling it.

Size

Black rat snakes are among the longest snakes in North America, regularly exceeding 1.5 metres and occasionally reaching over two. Racers are slimmer and shorter, typically to about 1.5 metres.

A very long black snake is almost certainly a rat snake, and the length itself is often what prompts the report — people describe a two-metre snake as enormous, which for this species it is not.

Climbing

Rat snakes climb well and are frequently found in outbuildings, roof spaces and up trees, which is where a large part of their diet lives. Finding a black snake in a barn loft or a soffit is entirely normal for the species.

Racers stay on the ground. A black snake three metres up a tree trunk has already identified itself.

Musk and bluffing

Both will musk and both will bluff. Rat snakes rattle their tail in dry leaves, producing a convincing buzz that gets them killed regularly, and this is discussed in rattlesnake or bullsnake where another harmless species does exactly the same thing.

Tail vibration is a widespread defensive behaviour in snakes and it is not evidence of a rattle.