Advice and guidance

[ConcinusMan]

I say it's not a Northwestern.

I'm going with T.e.vagrans(Wandering Garter Snake) I base it on those dots along the dorsal stripe.

I agree. Head is all wrong to be a northwestern. Definitely looks fairly typical for a WA wandering. (T. elegans vagrans)

The much larger head that is well offset from the neck, and like Steve said, the dots that sort of overlap the dorsal stripe, are a good way to tell them apart from northwesterns. Northwesterns have much smaller heads in relation to their body, and narrow snouts with sometimes a sort of "square" nose. Wanderings will have large broad heads that are more rounded.

I wouldn't keep them together. The wandering just might get irritated with the northwestern and eat it. Chances are pretty slim, but it does happen.