Brown or black snake
This looks like a garter snake. Snakes commonly coil when they feel threatened as a protective measure or may need to strike.
The snake in your photo is not a garter snake. It is an adult northern brown snake, scientific name (Storeria dekayi dekayi). It is a non-venomous species. Typical length is approximately 12 inches, and maximum length is approximately 18 inches.
This species has several subspecies. Their range extends from portions of Maine south to Florida, west to Texas and north to South Dakota. They are found in both hardwood and pine forests, elevated dry areas of swamps and margins of wetlands. They are also commonly found in garden beds underneath mulch, pine straw or leaf litter.
They feed primarily on earthworms and slugs, but they also feed on insects, spiders, snails (they pull the snail out of its shell before consuming them) and small salamanders.
Non-venomous snakes can coil in preparation for striking, but it is not necessary for them to administer a bite.
Here's a link to the Maryland Dept. of Natural Resources where you can find additional information on this species:
An excellent field guide for snakes in your area is:
Gibbons, Whit. (2017). Snakes Of The Eastern United States. Athens: The University of Georgia Press.
I hope this information helps, and thank you for contacting Ask an Expert.