Wednesday, August 9, 2017

Wrymouth and the Tasmanian Devils

In one of those odd, useless, meaningless synchronicities, after posting yesterday about poor little Wrymouth Possum--who died and, due to my fear of its infecting nicer possums with whatever it was dying of, has been incinerated--I went home and turned up an old news item I'd saved to remind myself to check for updates: the endangered species status of a similar but even uglier species, Australia's Tasmanian Devils.

The well-known cartoon "Taz" reflects a short description, not a serious study, of real Tasmanian Devils. They are carnivorous marsupials. They have some "devilish" qualities--they have no capacity for showing or recognizing affection; they are predators, not known to kill humans but well known to eat dead humans; if they're hungry they'll eat their own young. Up to fifty pups ("joeys") are born in one litter; only four can nurse at one time, so if little Tasmanian Devils had any empathy for their siblings they'd starve. Adult "devils" have black coats, reddish eyes, a peculiar gait (that doesn't keep them from moving faster than the average human, when they choose), raucous voices, and big heads and thick necks that allow them to chew up bigger animals' bones. They have been "tamed" to some extent but never become cuddly pets. Nevertheless, Australians find them useful because they quickly remove every trace of carrion.

The Wikipedia article about this endangered species is extensive and recently updated:

Two devils, sitting side by side, the one of left with a white stripe under its neck. They stand on a dirt patch. Stones can be seen in the background.
These Tasmanian Devils are not even trying to compete with possums on lack of visual my eyes, they're winning that contest! Photo donated to Wikipedia By Willis Lim -, CC BY-SA 2.0,

They don't actually spin around like little tornado clouds, but do share that hop-while-twisting-to-the-side threat display with the Virginia possum. They also have opposable "thumb" toes, on the forepaws where the animals can use their thumbs to hold food. (Virginia possums have thumbs on their hind paws and use them to hold on to branches when climbing. Tasmanian Devils apparently don't climb as much, and have fatter, less useful tails.) In some other ways their place in Australian ecology is analogous to those of swine, dogs, or hyenas in the rest of the world--and they don't coexist with dingoes.

Early researchers imagined that Virginia possums and Tasmanian Devils would belong to the same genus, meaning that with some encouragement from humans they'd be able to crossbreed. This has not turned out to be the case. The animals look somewhat alike but aren't closely related. If one of each species was put into one cage, the fast-moving, aggressive, carnivorous Tasmanian Devil would probably devour every trace of the slow-moving, peaceable, omnivorous Virginia possum. There's more than one way of winning, though...Tasmanian Devils are hostile but not truly solitary, while Virginia possums are truly solitary but not (usually) hostile, and this trait allows some Virginia possums to be domesticated. Although our possums are smaller animals with shorter life cycles, they often live two to four times as long, as pets, as they do "in the wild." They don't snuggle, as cats do, or lick hands, as dogs do, and they spend most of their non-foraging time (at night) finding different places to hide and sleep through the day, but they have soft inner coats and can become friendly with humans and domestic animals. Tasmanian Devils don't.

Recently, it seems, Tasmanian Devils have been turning up looking even uglier than is normal for them, due to bare, scabby, disfiguring tumors on the outsides of their mouths and faces. The tumors are described as a contagious form of cancer transmitted when the animals bite one another. Though most often seen on the sides of the face, the tumors can form inside the mouth, in skin on other parts of the body, or inside the animals where they're only found by dissection. The cancer can also metastasize into bones and organs.An Australian government PDF published for animal rescuers shows early stages of "Devils' Facial Tumour Disease" inside the animals' mouths looking more like small surface wounds than like abscessed teeth, but apparently the "tumours" can form anywhere and spread to anywhere else. The spread of this disease is selectively breeding more Tasmanian Devils with higher resistance--paradoxically, these individuals otherwise seem to be weaker, less dominant types. The cancer is thought to have killed most of the animals who were stronger, more dominant, and thus more likely to win fights.

Apparently fights happen fairly often because, although they don't hunt cooperatively, when one Tasmanian Devil finds meat it can't resist an urge to scream and snarl and call attention to itself, thereby attracting other Tasmanian Devils to gather around and fight over the meat. They can eat side by side without fighting as long as the supply holds out...but biting is what Tasmanian Devils do best. Compulsive competition for food seems to be what Tasmanian Devils have in the way of social life, and may serve some useful biological purpose. It looks almost like a moral fable--an illustration of how much better off the poor "devils" would be if they could at least eat carrion quietly, as Virginia possums do.

Three Tasmanian devils standing on bark chips huddled with their heads close together.
These three Tasmanian Devils were at peace with one another at the moment when they were photographed By Willis Lim -, CC BY-SA 2.0, ...but note the ear closest to the camera.
You might wonder whether such off-putting animals would be missed, but extinction is forever, and bone-crunching scavengers may do less harm to humans than carrion-eating flies do. The Australian government is still working to save a limited number of Tasmanian Devils.

I checked and found no evidence that "D.F.T.D." is spreading to North America. Virginia possums are protected from a tremendous majority of the diseases to which their diet and habits expose them, because their metabolism is slower and their body temperature is lower than other warm-blooded animals. Tasmanian Devils also have a slow metabolic rate, but if anything their healthy body temperature may run higher than a human's--it seems to vary. This might or might not mean that Virginia possums would be as immune to the diseases Tasmanian Devils get as they are to the diseases humans, cats, dogs, and cows get. 

Warning: The fact that possums themselves do not share diseases with other warm-blooded animals does not mean that possums can't carry diseases to other warm-blooded animals. They can. A possum that has been doing its ecological job, eating nasty stuff, will have fresh bacteria and protozoa stuck to its paws and fur; even after those disease agents drop off and die, the possum is likely to carry fleas and ticks that may transmit pathogens between other animals. The only animals that ordinarily get any kind of disease carried by possums are horses, but when humans handle possums they are creating an extraordinary situation where anything is possible.

Another possible explanation of why poor little Wrymouth Possum was so sick and ugly, so friendly to an unknown human, and so hostile to an inoffensive kitten, is Metabolic Bone Disease, a catchall term for nutrient deficiencies sometimes found in wild possums, and very often found in pet possums reared on inadequate diets. Seems some humans who try to adopt young possum-pups try to feed them as if they were kittens. (In fact, given a choice of foods, some possums will choose a vegetarian diet for weeks on end; one LiveJournal blogger lived with a pet possum who wanted to live on peaches and cream, or rather yogurt. Despite the preponderance of nasty stuff in their natural diet, possums love fruit and probably need it.) These possums become malnourished and may become "vicious" or even "cannibalistic." Their bones and teeth fail to develop normally, all sorts of other things go wrong, and the poor little things aren't even fit to correct their own nutritional imbalances when the frustrated would-be rescuer "releases them into the wild." They have no idea what they need to eat and may not be strong enough to take it when they find it. 

I can't muster a lot of respect for this organization's policy of "We'll tell you how we rear viable possum-pups if and when you pay us $25 per year for a membership fee," but for anyone who really wants to cuddle a possum, a limited amount of information is found at this web site:

If all that was wrong with Wrymouth was a dietary deficiency...No. Wrymouth was too big, too dangerous to kittens, and too far gone, for me to have tried to cure it. All I really regret, in my short acquaintance with this possum, is having been too ill to take it somewhere out of my animals' sight and end its sufferings. But I can warn readers that if you adopt and inadvertently malnourish a baby possum, you too may create a monster like poor Wrymouth. Possums can live on almost anything but they don't thrive on an all-protein diet. If you're going to teach an animal with no natural instinct to cuddle that inviting you to groom and pet it is a good way to solicit food treats and/or lose ticks and fleas, you might at least feed it right...or, failing that, at least euthanize it yourself and instead of dumping it out, even near the homes of animal rescuers.