That is interesting, the he is probably actually a she, some of my larger females will take F/T adult mice with ease, but I've never tried live nor would I want to, could be dangerous, because garters aren't constrictors the just catch and overpower prey. That big girl in your garden must have figured out how to averpower adult mice quickly and swallow them without getting bitten or clawed too much, huh. Neat story thanks for sharing.
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Jeff Benfer
gartersnakemorph.com