The photo above is an example of a so-called “wooly snake”, Pseudoserpente canuckistanensis. As you may have already guessed, in spite of its legless condition Pseudoserpente is not a snake, but is in fact a mammal, albeit one with an interesting history.
The skeleton of Pseudoserpente reveals its true relationships; it is a member of the Mustelidae, the carnivore family that includes ferrets and weasels. But remarkably, the wooly snakes have lost all traces of both the anterior and posterior limbs, even including the pelvis and the shoulder girdle. In this respect, they are more completely legless than even the boas, which retain pelvic remnants.
This seems to be an adaptation to the wooly snakes’ challenging habitat; they only live in a narrow swath of land across Canada and Alaska, at the margin of the permafrost. During the summer this area becomes a marsh, and movement is difficult. Pseudoserpente is able to crawl through these areas at an amazing rate of speed using body undulations, with no legs or claws to get entangled in vegetation. While they are capable of swimming (as with the captive example below), wooly snakes don’t typically enter open water or dry land; they stick to inaccessible marshes (which is why they’re spotted so rarely).
The other unique Pseudoserpente character is the shape of its teeth, specifically the carnassials. In Pseudoserpente the medial sides of the lower carnassials (the first lower molars) have numerous long flexible dentine fibers that reach all the way to the midline of the mouth, meeting the fibers from the corresponding tooth on the other side of the jaw to form a dentine net. Wooly snakes are filter feeders; they crawl through pools in the marsh with their mouths open, trapping mosquito larvae in the tooth mesh. They also take in a lot of plant material, which is not digested; Pseudoserpente droppings were originally thought to be from an herbivore.
Wooly snakes are major predators of mosquitos. In areas where the Pseudoserpente population has declined, caribou populations have also dropped; the caribou are literally sucked dry by the vast numbers of mosquitos when wooly snakes aren’t present to keep the population in check. It’s actually possible to roughly track the health of wooly snake populations from aircraft by looking for large numbers of dead caribou.
Even this is not the most remarkable Pseudoserpente feature. Notice the red eyes in the two live animal photos above; this is not a photographic “red-eye” effect. Wooly snake eyes actually emit focused near-infrared light (and far red, which is why we can see them glowing). As they crawl through the swamp, they ramp up their eyes’ infrared output to the point that the water is close to boiling (~95 C). The mosquito larvae filtered by wooly snakes are cooked before they are eaten! Incidentally, this was how Pseudoserpente droppings were first recognized; the plant material was cooked, unlike that from herbivores.
(Also incidentally, some folks have suggested that Pseudoserpente is responsible for the melting currently occurring in the Arctic permafrost, rather than anthropogenic causes. This is incorrect; even as hot as wooly snakes are, their total energy output is insignificant relative to the amount of heat necessary for observed permafrost melting.)
Modern Pseudoserpente were first described by French-Canadian naturalist Pierre Abruti d’Avril in 1818. The wooly snake fossil record only goes back to the late Pleistocene along the southern edge of the ice sheet; their fossils are known from North Dakota, Wisconsin, and Minnesota (a small relict population still lives in the Boundary Waters area along the Minnesota/Ontario border). Apparently all the older fossils of this lineage were scoured away during the Pleistocene glaciation.