I have removed the crickets and am putting earthworms in the tub. It appears the snakes are actually eating them, as the worms are disappearing and the snakes both look like they have increased in girth. I have tadpoles; I might try putting a bowl of tads in the tub and see if that is an option.
Also have found several small ensatina salamanders but just can't bring myself to feed those to the snakes.