Adult alligator snapping turtles have no natural predators other than humans. Their massive size, armored shell, and powerful jaws make them essentially invulnerable once fully grown. Eggs and hatchlings are a different story — raccoons are the primary nest predators and can devastate nesting success. Hatchlings and small juveniles face predation from large fish, river otters, wading birds, and raccoons. The phorid fly (Megaselia scalaris) can infest nests, with larvae damaging eggs and killing emerging hatchlings. Fire ants (Solenopsis invicta) may also threaten pipping and emerging hatchlings.

Alligator snapping turtles don't truly hibernate, but their activity drops significantly during the colder months. They remain in the water year-round and can tolerate fairly cool temperatures, though they become less active in winter. On warm winter days, they may still forage along the bottom and shoreline. The species thermoregulates primarily by adjusting its depth in the water column rather than basking, and aerial basking has been documented only once.

These turtles are opportunistic carnivores with surprisingly varied diets. They're perhaps best known for their unique fishing technique: lying motionless on the bottom with jaws agape, wriggling a pink, worm-shaped lure on their tongue to attract fish into striking distance. The camouflaged interior of the mouth — grayish-brown with black speckles rather than the typical turtle pink — completes the ambush setup.

But lure fishing is primarily a juvenile strategy. As the turtles grow, the lure becomes proportionally smaller and less conspicuous, and adults shift to more active foraging, particularly at night. A Louisiana study found that the majority of stomach contents by volume were actually oak acorns, with fish being the most frequently eaten item but contributing only about 7% by volume. Other prey includes other turtles, mollusks, crayfish, snakes, frogs, aquatic birds, and even small mammals like raccoons, muskrats, and armadillos that venture too close to the water's edge. They've even been known to take small American alligators. As seed dispersers of oak trees, these turtles may play an important ecological role — ingested acorns have been shown to germinate faster after passing through their digestive system.

Mating occurs yearly, in early spring in the southern part of the range and later spring farther north. Males mount females from behind, grasping the shell with all four feet. Courtship involves considerable sniffing and occasional biting. About two months after mating, females make one of their rare overland trips to construct a nest.

In Florida, the nesting season runs from late April through mid-May, with females preferring warm, humid early mornings, particularly following rain. Nests are typically within 20 m of water but can be as far as 200 m during dry years. Females produce a single clutch per year of 8–52 eggs (mean of about 35 in well-studied Florida populations), and some females skip years entirely. The nearly round eggs weigh about 26 g and measure 32–41 mm in diameter.

Incubation takes 100–140 days, with most eggs hatching in about 105–110 days. Sex is determined by incubation temperature: 25–27°C produces mostly males, while 29–30°C yields only females. Hatchlings emerge in late summer to early fall and do not overwinter in the nest.

The vermiform tongue lure is the headline feature — no other living turtle has anything like it. This pink, worm-shaped appendage wiggles convincingly on the floor of a camouflaged mouth, turning the turtle into a living fishing trap. The interior of the mouth is uniquely pigmented in grayish-brown with black speckles rather than the typical pink, completing the illusion.

But the superlatives don't stop there. This is the largest freshwater turtle in North America and among the heaviest in the world, with only some Asian giant softshell turtles reaching comparable sizes. The bite force is formidable, ranging up to 1,872 Newtons in large individuals — enough to cleanly sever human fingers and bite through a broom handle. The supramarginal scutes along each side of the carapace are found in no other living turtle species, though they occur in some long-extinct fossil turtles. And these animals are remarkably long-lived: the oldest captive individual survived over 80 years, and wild individuals are believed capable of reaching 80–120 years or more.