Instructions
Look at the size of the garter snake. Females are much larger than male garter snakes. If the garter snake is over two feet long, it is almost definitely a female.
Observe the width of the snake. A female garter snake is much bulkier than a male one.
Observe the garter snake's activity. Males are much more active than females, as females conserve their energy for reproducing.
Look at the snake's tail. A male garter snake will have a wider tail base.
Use probing if observing the appearance doesn't resolve the issue. This should only be done by those experienced in probing as it can negatively affect the snake. A surgical probe inserted into the garter snake's vent will only go up two or so scales' length on a female and much further on a male.
How to Tell the Difference Between Male and Female Garter Snakes
Garter snakes, often referred to as gardener snakes, are very common and quite often kept as pets. They are easily tamed but it is not as easy to identify their sex. Determining if your garter snake is male or female can be useful for many reasons, such as deciding on a name or in case you ever decide you'd like to breed garter snakes.