There are a few ways to tell the difference between male and female Terrapins this can include:
Tail length
Male Terrapins have longer, thicker tails, while females have shorter, thinner tails.
Size
Female Terrapins can grow to be much larger than males. For example, an adult female Diamondback Terrapin can be nearly twice the size of adult males, with a shell length of about 12 inches compared to 6 inches for a male.
Head size
Older female Terrapins can have enlarged heads with strong jaws.
Plastron
The bottom of a Terrapins shell is called the plastron, which can also be used to determine the gender. Males have a concave (curved in) plastron, while the females have a flat one.
Anal scoots
The anal scoots on the plastron are not as widened as they are in the males. They are a little bit more of a sharper V.
The size difference between most male and female Terrapins may not always be obvious until the Terrapins reach sexual maturity. The diet can also play a role in the size of the Terrapin.
