My wife called the HD where we bought them (soil and snake) and the manager was very straight forward. He had been seeing quite a few "critters" coming in on soil and mulch pallets during the past year or so. These included snakes, scorpions and at least one tarantula. This was his first report of a snake inside of a bag. He apologized and said he would pass it on to the supplier. He also said he was pretty sure the snake was in the Miracle Grow because the topsoil was probably too packed and the garden soil contained some nutrients and organic material that would sustain the snake.
Then I ran across this:
Yikes! Be careful out there!!!