snapping turtle

(click to enlarge)
Common snapping turtle (Chelydra serpentina). (credit: Walter Dawn)

Either of two species (family Chelydridae) of edible, omnivorous, freshwater turtles found in North and Central America. They are tan to black and have a rough upper shell, a small cross-shaped lower shell, a long tail, and a large head with hooked jaws. Known for their fierceness, they lunge at aggressors and prey and bite them with their powerful jaws. The common snapping turtle (Chelydra serpentina) has a shell 8 – 12 in. (20 – 30 cm) long and weighs 10 – 35 lbs (4.5 – 16 kg). The alligator snapping turtle (Macroclemys temmincki), the largest freshwater turtle in the U.S., has a shell 16 – 28 in. (40 – 70 cm) long and weighs 40 – 155 lbs (18 – 70 kg). It lies quietly on the bottom of slow moving bodies of water, luring fishes by means of a wormlike appendage on the floor of its open mouth.

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Chelydra serpentina

TAXONOMY

Testudo serpentina Linnaeus, 1758, "Calidus regionibus" (warm regions). Two subspecies are recognized.

OTHER COMMON NAMES

English: Common snapping turtle; snapper; French: Chélydre serpentine; German: Schnappschildkröte; Spanish: Tortugalagarto común.

PHYSICAL CHARACTERISTICS

The carapace of these large turtles, to 19.3 in (49 cm), bears three low, knobby keels (except in the oldest individuals). The shell is dark, although it may range from brown to olive to black. The head is large, the upper jaw is somewhat hooked anteriorly, and the eyes open dorsolaterally (toward the top and side of the head).

DISTRIBUTION

Ranges extend from southern Canada across the United States east of the Rocky Mountains to New Mexico, Texas, and

Florida. Tropical snapping turtle populations (until recently considered subspecies of the snapping turtle) range from Veracruz, Mexico, through Central America to western Ecuador in northwestern South America.

HABITAT

Snapping turtles inhabit nearly any body of freshwater within their range, although they also invade brackish water environments in many areas. They seem to prefer warm, shallow, still water, with soft bottoms and abundant aquatic vegetation.

BEHAVIOR

Snapping turtles are highly aquatic, spending most of their time lying camouflaged in the mud in shallow water. Most active during the morning and early evening, these turtles are often active at night in the south, but rarely so in the north. When active, they are primarily bottom-walkers, slowly moving over the bottom in search of food or mates. Most thermoregulation is done by selecting warm, shallow, submerged sites; however, they occasionally bask by floating on the water's surface or even by climbing out of the water onto emergent logs or other objects. They may be active year-round in the south, but hibernate for half the year or more in the north. However, some individuals may be active in the north in midwinter under thick ice cover. In addition to nesting forays by females, snappers frequently travel great distances overland between bodies of water (often almost a mile). They also make equally impressive movements in the water, one observed female moved 2.1 mi (3.4 km) in just 10 days.

FEEDING ECOLOGY AND DIET

Although snapping turtles are probably carnivorous by preference, they can subsist on diets ranging from completely carnivorous to completely herbivorous. Animal foods include sponges, flatworms (planarians), earthworms, leeches, clams, snails, crustaceans, spiders, insects, amphibians and their eggs and larvae, snakes, other turtles, birds, small mammals, and carrion. Snapping turtles also eat algae, duckweed, and other submergent and emergent aquatic plants and their seeds.

REPRODUCTIVE BIOLOGY

Mating is known to occur from April to November, but probably peaks in the spring and fall. Courtship is highly variable, from the male directly mounting the female from behind, to the male trailing along after the female for several minutes before mounting, to face-offs, head-swaying, and/or water gulping and belching before mounting. Eventually the male mounts atop the female's shell and swings his tail under hers to mate. At high latitudes, nesting begins in early June and may extend to early July, whereas at low latitudes it may extend from late April to early June. Females may nest within a few feet of the water's edge or travel overland as far as 9.9 mi (16 km) to nest. The nest is dug (and covered) with the hind feet, and because of its size and depth (to 9.8 in [25 cm]), even a covered nest is quite obvious. Consequently, nests are heavily predated by animals, most within 24 hours of construction.

Females produce at most one clutch per year, with some females apparently skipping some years. They lay spherical, hard-shelled eggs that average 1.1 in (2.8 cm) in diameter and 0.4 oz (11 g) in mass. Egg size does not seem to increase significantly with female size. Clutch size is highly variable, ranging from six to 109, averaging about 32 across the range, and is positively correlated with female body size, latitude, longitude, and elevation (the largest clutches are laid in western Nebraska). Incubation in nature requires 55–125 days (more typically 75–95) depending on nest temperature (development being faster at higher temperatures) and geography (incubation times being longer in the south). Hatchling snapping turtles usually emerge from the nest in the late summer and fall (August to October) and move directly to the water. Hatchlings in northern populations that do not emerge in the fall before the onset of cold weather almost never survive the winter, probably because of their low tolerance of subfreezing body temperatures. High and low incubation temperatures result in the production of all-female offspring, and intermediate temperatures produce all males. Because their clutches are so large, eggs in different parts of the same nest may produce different sex ratios, e.g., all females at the top and all males at the bottom.

CONSERVATION STATUS

This species has such an extensive range and is so prolific that it has so far been able to persist even in habitats significantly altered by humans.

SIGNIFICANCE TO HUMANS

Snapping turtles are exploited by humans primarily for their meat, although some small individuals make their way into the pet trade.

The noun has one meaning:

Meaning #1: large aggressive freshwater turtle with powerful jaws