COMMON SNAPPING TURTLE (Chelydra serpentina) LINNAEUS, 1758
IDENTIFICATION: The snapping turtle is a large easy to recognize turtle with some specimens weighing in excess of 35 pounds (16 kg) and a straight-line carapace length of 8-14 inches (20-36 cm). A few long-term and well-fed captive specimens have been known to occasionally weigh in excess of 70 pounds (32 kg). The tan to dark olive brown carapace is round in dorsal view with three longitudinally oriented keels and radiating dark lines on each scute of the carapace. The lines extend anterior to anterior-laterally from each side of the medial keels found in the center of each scute. As the turtle ages, these markings fade into the base coloration of the shell. The dorsal keels are also more noticeable on younger specimens and tend to lose definition and become worn smooth with age. The posterior marginal scutes are serrated and the plastron is significantly smaller in size than the carapace. The neck is long and the head is large with two barbels present on the chin. The legs are well developed and powerful. 10 wide antebrachial scales are present on the front of the forelimbs. The front and hind feet each bear five thick and well-developed claws with webbed toes. The tail is long, measuring the same length of slightly longer than the carapace and has three dorsal rows of 12-15 longitudinally oriented scales. The most prominent of these scales are the center row of which the largest is just above the cloaca and from there they are reduced in size with the smallest just before the tip of the tail. The ventral surfaces are an almost uniform wash of beige to creamy yellow. The plastron is greatly reduced and cruciform in shape. The reduced plastron allows a great amount of mobility for the limbs. Among well fed specimens, prodigious amounts of fat can be seen accumulated near the hind limbs. Perhaps a reduced plastron permits snapping turtles to periodically engorge themselves when the opportunity arises.
Hatchlings are identifiable by their small size, uniform dark coloration, wrinkled and rugose carapace with white accents along the marginal scutes. An umbilical scar on the plastron is sometimes present among baby snapping turtles that have recently hatched and left the nest. Of 283 hatchlings measured the mean carapace length was 28.8 mm (range of 16.4-38.1 mm) and the mean carapace width was 23.6 mm (range of 21.5-29.2 mm) (Ernst and Lovich, 2009).
GEOGRAPHIC DISTRIBUTION: Snapping turtles have a natural geographic distribution extending from southern Canada into the United States east of the Rocky Mountains. In the United States it has been introduced and established in Arizona, California, Nevada and Oregon. Internationally it has been established in China, Japan, and Taiwan. In Texas, they are mostly distributed throughout the panhandle and bodies of water east of the Pecos River. Records from west Texas and the Rio Grande Valley (Hidalgo, County) are due to released specimens. At this time, it is unknown if these locations contain reproductively active populations.
BEHAVIOR AND ECOLOGY: Snapping turtles are found in essentially every type of freshwater habitat. Ponds, slow-moving creeks and rivers, lakes, ditches and brackish marshes are suitable environs for snapping turtles. A body of water with a soft, muddy bottom, accumulated leaf litter or abundant aquatic vegetation is preferred. In bodies of water with a muddy substrate, one can sometimes encounter snapping turtles covered in mud with only the eyes and nostrils exposed. In this position, the snapping turtle is well poised to ambush unsuspecting prey. Not only does its long neck allow the turtle to ambush prey, it also allows a concealed snapper to raise its nostrils to the surface without disturbing its hiding place. Snapping turtles are opportunistic predators and scavengers that consume a wide range of food items including but not limited to: algae, duck weed, water hyacinth, water lettuce, crayfish, insects, fish, amphibians, reptiles, birds and mammals.
Although considered unpopular by many fishermen, snapping turtles are not known to be detrimental to overall fish populations.
Males and females are easy to distinguish. Mature male specimens are larger than females and the opening of their cloaca extends beyond the marginal scutes of the carapace. Some males will evert their phallus when picked up, this is a common response to being lifted. The opening of the female's cloaca is often well within the perimeter of the posterior marginal scutes. Vigorous bouts of courtship and mating displays most commonly take place in the water from April to May but mating behavior can occurs throughout the year.
Females generally lay 20-40 spherical eggs each spring. Typical incubation requires 75-95 days. Variation in incubation time can be due to the latitude at which the eggs were laid. Depending upon climatic conditions outside the nest, newly hatched babies sometimes remain inside their nest chamber until the following spring.
Snapping turtles lack sex chromosomes and the sex of a baby snapping turtle is determined by the incubation temperature. Incubation temperatures of 29-31°C resulted in all females, while males were produced when incubated at 23-24°C and both sexes were produced when incubated at 25-28°C. However, this temperature range mostly produced males at the lower range of temperature (Janzen, 1992).
Snapping turtles are mostly aquatic but occasionally leave the water to bask or venture about on land. Activity out of the water most commonly happens after heavy rains, during drought when individuals are searching for water, or when females are looking for suitable nesting sites. In September of 2000, Michael Smith and I found a dead adult specimen in the dried lotus marsh at the Fort Worth Nature Center as well as a set of tracks left in the dry mud that reached the channel of the Trinity River approximately .25 miles away.
When encountered or approached underwater, snapping turtles will most often turn and swim away. However, they are not as fast as a human swimmer equipped with fins. Whenever disturbed on land the turtle will demonstrate one or all of the following behaviors: attempted escape, deep hissing breaths, flatulence, releasing a foul-smelling musk, raising its’ body high off the ground and then positioning the carapace at an angle towards the perceived threat and of course by rapidly lunging and striking its’ neck forward with its’ jaws open. The long neck can reach backwards to almost the center of the carapace.
Safely handling an adult requires a combination of skill and knowledge of the turtle’s behavior. Holding and supporting them by the tail is discouraged as it can cause serious damage to the tail. Holding them by the central part of the shell similar to the way most turtles are held is rarely practical as snapping turtles will use their well-developed claws and powerful legs to scrape and claw the hands of the person holding them. Another challenge to safely holding one is the weight of the turtle. Safely handling 20-40 pounds of clawing, musk exuding and striking turtle for most people is a challenge better left unanswered. Holding them by their back legs offers the safest option for supporting their weight while carrying them a short distance. Asides from those studying turtles or wanting to safely move one off a road there is very little reason or need for picking this turtle up.
The sharp cusp and powerful bite can deliver a serious injury. Turtle biologist Eric Munscher suffered a broken thumb and laceration after being bitten by a 40-pound male. However, the most serious anecdotal injury I am aware of happened to my great uncle and it was a story told to me by my mother and my grandparents. It took place the 1930's in the Brazos river near Marlin, Texas when my grandfather and his older brother were checking trot-lines at night. They were walking barefooted in the river when a “big turtle” bit off his big toe. They never captured the turtle and the only description I ever heard was that the turtle was “big”. The culprit was most likely an adult snapping turtle. No other species of turtle in the Brazos River would be capable of delivering such an injury. Another anecdote worthy of mention involves a 1990 robbery of a Balch Springs, Texas Domino’s Pizza delivery driver robbed of his cash. The thief’s weapon of choice, a live adult snapping turtle held to the driver’s head!
To a lesser degree of risk to one handling a snapping turtle, adult males will often evert their phallus when picked up. The exact cause of the physiological function is unknown but awareness of this can be useful knowledge; especially for wildlife educators wishing to avoid a suite of uncomfortable questions from an audience of children.
In 2018 the legal commercial collecting of snapping turtles in Texas came to an end. However, up to six turtles per year can be taken for personal use with a non-game hunting license. This regulation is a vast improvement over the previous years when unlimited collection from the wild for foreign markets was allowed.
Ernst, Carl H.; Lovich, Jeffrey E. 2009. Turtles of the United States and Canada, 2nd edition. Johns Hopkins University Press, 827 pp.
Janzen, Frederick J. 1992. Heritable variation for sex ratio under environmental sex determination in the common snapping turtle (Chelydra serpentina). Genetics 131: 155-161