I may have found the killer of my easterns... Low humidity.
I've noticed in the past that some species faired better than others in the outdoor pen. Those from dry climates, checkereds, wanderings, and radii, tended not to fair so well as my butler's, easterns, and red-sideds. I'm thinking that humidity may have more to do with garter care than I previously thought. Our climate is very wet here; In the house it's always above 60%. I'm thinking that species from cooler, wetter climates thrive here due to the humidity, for whatever yet to be discovered reason. Butler's garter snakes are found in this "belt of humidity." During the summer, I sent 5 baby butler's to Don. Within 3 month's time, *all were eating fine on worms mind you* all of them had perished. Don had sent me a few checkereds and a red-sided. One of the checkereds was older and the red-sided has to be around 2 years old. The checkereds have since perished while the red sider continues to thrive.
After all of this, I'm thinking that juvenile garter snakes are the most adaptable to climate change, while adults and babies aren't so much.

Comments?