I was recently given some shed snake skins that were found at the CWRU Farm in northeast Ohio. These sheds will provide a fun way to teach CWRU herpetology students snake identification skills. Shed snake skins have a number of characters that can be used to identify the species of snake.
I looked closely at the scales to determine whether they were keeled or smooth. Keeled scales have a small ridge running down the middle, whereas smooth scales lack the ridge. By examining this close-up view of the scales in the photo of this shed, you can see that they are smooth. Since this shed has smooth scales, we can rule out several additional species, including the Northern Water Snake and the Garter Snake. We can also rule out the Black Rat Snake, as it has weakly keeled scales.
This leaves a couple snake species that could be the source of the shed: Eastern Milk Snakes and the Black and Blue Racers (which are geographic variants of the same species). To separate the remaining snakes, we need to look at the anal plate. The anal plate is the last of the large belly scales on the snake’s body, and it is located directly over the snake’s cloaca (excretory and reproductive orifice). The photo below shows the anal plate (circled). In this photo, the snake’s head would be to the right, and the tail would be to the left.
As you can see from the photo, the anal plate on the shed is single, not divided. Racer snakes have divided anal plates, but Eastern Milk Snakes have single anal plates. So this snake ends up as an Eastern Milk Snake (Lampropeltis triangulum):
Interested in using scale traits to identify snakes? You can find all the information you need in the Peterson Field Guide to Reptiles and Amphibians of Eastern and Central North America or the Field Guide to Western Reptiles and Amphibians.