There are few more intimidating and mysterious animals in North America than the Alligator Snapping Turtle, Macrochelys temminckii. And few are more deserving of this aura than the mighty Alligator Snapping Turtle: Adults reach a whopping 175 pounds, are characterized by a row of nasty looking spikes down their back, and have a bite that is fully capable of breaking a broomhandle in half. Did we mention that one of their prey items is alligators (admittedly, small ones)?
Like all turtles, Alligator Snapping Turtles are long-lived. They do not achieve sexual maturity until approximately 11-13 years old (Dobie 1971), and they've been known to live at least 70 years (Gibbons 1987). I've always heard stories about a snapping turtle caught in the 1980s with a Civil War Era bullet lodged in its shell, but I'm essentailly unable to confirm that story (google has failed me).
Snapping turtles tend to attract amazing stories. According to unverified reports, the largest alligator snapping turtle ever was caught right here in Kansas, on the Neosho River, and weighed in at over 400 pounds. The largest verified specimen was 236 pounds, and I can't even imagine what I would do if I was dragging a seine net up and realized that a 200 pound snapping turtle was slowly crawling along the net towards me. I'm always a little freaked out by pulling up small common snapping turtles.
Oh, what was that? You didn't realize there were two kinds of snapping turtle? The far more numerous Common Snapping Turtle, Chelydra serpentina, is a totally different species. There are a lot of fairly obvious morphological differences (no spines on an adult common), you can see them side-by-side here. If you live in Kansas, the odds are you've never seen an Alligator Snapping Turtle in the wild. The common snapping turtle gets big (25-30 pounds in the wild), but not nearly as big, and frankly, that's part of what makes the alligator snapping turtle so much more awesome.
This is a 1-year old! (source)
So if you're a hundred pound turtle with no natural predators, what do you spend your time doing? Finding enough to eat! A study in Arkansas and Louisiana found a huge list of food items in the guts of 109 sampled individuals. By far the most abundant item was fish, but there were also crawfish, molluscs, other turtles, insects, Myocastor coypus (nutria), and even armadillos, possums, squirrels, hogs, snakes, eggs, and vegetation (adults are somewhat omnivorious; Elsey 2006). In all likelihood, several of these species were consumed post-mortem. Other studies have found acorns to be a significant source of food (see citations in Elsey 2006). In captivity, alligator snapping turtles have eaten just about anything put in front of them.
I wouldn't recommend trying this at home. (source)
Alligator snapping turtles are a uniquely North American species, and are restricted to river systems draining into the Gulf of Mexico. Which isn't to say these aren't extremely mobile guys. Unlike common snapping turtles, alligator snappers stick almost exclusively to large river systems. Instead of swimming they seem to mostly get around by just walking on the bottom of the river, which isn't the same as saying they don't swim at all. Individuals have been shown to move 27-30 km in a 3-year span and 16 km in a 2-month span (discussion in Shipman and Riedle 2008). That may not seem like a lot until you consider that individuals prefer to spend most of their time hiding out in cover, and get around by walking along river bottoms.
Despite all that movement, individual river systems seem to have genetically distinct populations of snapping turtles. Roman et al. (1999) found that 12 drainages had unique genetic characteristics, thereby justifying their management as separate units. This is probably explained by the fact that these turtles have never been found to move through terrestrial habitats (again, unlike common snapping turtles). In fact, common snapping turtles seem to be one large, genetically similar population across virtually all of North America.
Alligator snapping turtles are protected at the state level to some degree everywhere they occur, but have repeatedly failed to achieve federal status. This is borderline astonishing, since a wide range of data suggests that the species has been in rapid decline since the 1950s, continues to be threatened by the development of dams, and is considered a culinary delicacy in many parts of the United States. Overharvesting has been shown to dramatically affect the population structure of the species, even decades later. As with many other long-lived species, it is generally believed that the loss of reproductive adults will take a long time to recover (as I mentioned above, it takes over a decade for an individual to reach maturity). Within Kansas the Alligator Snapping Turtle is a Species in Need of Conservation.
Dobie, J.L. 1971. Reproduction and Growth in the Alligator Snapping Turtle Macroclemys temmincki (Troost). Copeia 4:645-658.
Elsey, R.M. 2006. Food habits of Macrochelys temminckii (Alligator Snapping Turtle) from Arkansas and Louisiana. Southeastern Naturalist 5:443-452.
Gibbons, J.W. 1987. Why do turtles live so long? BioScience 37:262-269.
Shipman, P.A. and J.D. Riedle. 2008. Status and distribution of the Alligator Snapping turtle (Macrochelys temminckii) in Southeastern Missouri. Southeastern Naturalist 7:331-338.