That is 100% guaranteed a garter snake. There are quite a few different garter snake species and they do not all look alike. They do not eat other snakes that I'm aware of...but they do eat fish and worms and the like. Most garter snakes do not stay 1-2' either...ribbons do...garters mostly get ~3'...some even 4-5'. I would not see a garter as much of a threat to anything unless you have a pond with small fish. Also, we DO have garters very similar in coloration to that snake in the Northeast US.