Snapping turtles, which include the widespread common snapping turtle (Chelydra serpentina), exhibit distinct physical differences between sexes once they reach maturity. Determining the sex of these animals requires close observation of several physical characteristics. The differences are not apparent in hatchlings or young juveniles, making external sexing difficult until the animal is older and larger. Accurate identification relies on a combination of size, tail structure, and shell shape.
General Size Differences
Sexual dimorphism in snapping turtles often manifests through overall size, with males generally attaining a greater mass and carapace length than females. Adult males typically reach a body mass between 10 and 35 pounds, compared to 10 to 20 pounds for females. A male’s carapace, or upper shell, often measures 10.5 to 13 inches in length, slightly exceeding the 10 to 11.5 inches typical of mature females. While this difference provides a general indicator of sex among full-grown individuals, size alone is not a guarantee of sex, especially when comparing turtles from different geographical areas.
The Key Indicator: Tail and Cloaca Placement
The most reliable non-invasive method for determining the sex of a snapping turtle is by examining the tail’s morphology and the location of the cloaca, or vent. Males possess a tail that is noticeably longer and thicker than a female’s, a structure necessary to house the reproductive organ. This thickness often creates a visible bulge at the tail’s base. The cloacal opening in a male is situated farther down the tail, extending well past the edge of the carapace when viewed from below.
In contrast, females have a shorter and thinner tail structure. The female’s cloaca is located much closer to the body, often appearing near or directly under the rear margin of the plastron, the turtle’s lower shell. The distance from the cloaca to the plastron’s edge serves as the primary external measurement for sexing adult and subadult snapping turtles. The relative size of the tail compared to the carapace length is a more consistent marker than overall body size.
Plastron Shape and Shell Size
Less reliable, but still indicative, differences can be found in the shape of the plastron and the overall shell structure. The plastron of a male may exhibit a slightly concave, or inward-curving, shape. This slight concavity facilitates mounting and maintaining position on the female’s carapace during mating. Females, who must accommodate developing eggs, typically have a plastron that is flat or slightly convex (outward-curving).
The overall dimensions of the shell opening also provide subtle clues. The space created by the plastron and carapace where the tail emerges is generally wider in females to accommodate egg-laying. These shell-based characteristics are often subtle and can vary significantly between individuals, making them secondary indicators.
When Sexing Becomes Possible
External sex differences are not apparent in snapping turtle hatchlings and young juveniles because secondary sexual characteristics develop with maturity. Accurately sexing an individual requires waiting until it has reached a specific size threshold. For the common snapping turtle, this point is generally reached when the carapace length is at least 8 to 10 inches, corresponding to the size at which they attain sexual maturity. Depending on the environment, reaching this size can take approximately 5 to 7 years in warmer climates, or up to 12 to 20 years in northern populations.
Attempting to check the cloaca position requires safely handling the turtle, which demands caution due to their powerful bite and flexible neck. Examining the tail and plastron should only be done by experienced individuals who understand the necessary safety precautions for handling such a defensive animal. Before the turtle reaches maturity, sex identification typically requires more invasive methods, such as an internal examination by a veterinarian or researcher.