Garter snakes are very sexually dimorphic as adults. 99 % of the time I can accurately sex an adult garter snake before I have even picked it up. Females are bulky, they get much larger than males, they usually have a wider, bigger head, chunky body, Really big, exaggerated upper labial scales, are usually gravid when found in mid-summer, and have a petite tail that ends rather abruptly. Males are small and petite, They usually have little heads and a narrow look to their face, and even well fed males tend to stay slender even when compared to a non gravid female of the same length. Their tail is basically a dead giveaway, it is much longer and thicker at the base and continues to be thick for sometime before it tapers off. They don't require nearly as much food as a female and usually aren't quite as voracious as the ladies.
A good shot to tell us if she's gravid would be from above of just the snake with nothing hiding any part of her body. The bill is not necessary as I have a pretty good idea of her size based on her head shape
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