Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"

The animal I show you today is again an American – a Virginia Opossum, or sometimes just 'Possum', Didelphis virginiana! The scientific name means 'two-womb from Virginia' which I'll explain later. This species is almost entirely restricted to the USA, but it enters southern Canada as well as Central America, as far south as Costa Rica. It is actually expanding its range, mainly northward; it also now occurs along the western coast of the USA, where it hadn't, originally. It has generally benefited from humans, on which more later.

First, let's again look at the taxonomy of this animal! An opossum is, first of all, a marsupial. Marsupials are one of the three 'big' groups into which mammals are classified. The first is the Monotremes, which include the Platypus and the Echidnas and which are the only surviving egg-laying mammals. The second is the Marsupials, which don't all have a pouch, but all of which can carry their young just for a very short period in the womb, and then 'birth' them in a very undeveloped form – almost at a fetal stage. Most have pouches into which they then transfer their young where they remain to develop more fully. I'll say more about marsupial reproduction later. The third group of mammals is the Placentals, which is us! And cats and dogs, cows and horses, mice, rats, squirrels, shrews, hedgehogs, bats, monkeys, apes, whales, seals, dugongs, pangolins, hyraxes, elephant shrews � you get the picture. Placentals are by far the majority of mammals, and they all carry their developing young in the womb for a much longer period, feeding them through their complex placentae, so that they reach a much more developed condition before being born. Marsupials actually also have placentae, but they're much simpler than those of placentals.

Monotremes split off from the marsupials and placentals likely sometime in the Jurassic; the placentals and marsupials likely split from each other in the Cretaceous, and the oldest known true marsupial is about 110 million years old. Marsupials once occurred worldwide, but placentals started to dominate after the extinction of the dinosaurs 66 million years ago. Marsupials kept flourishing mainly in two places – South America, and Australia. Both of these had split from the other continents around the late Cretaceous. In South America, marsupials survived along with placentals, and mainly 'chose' lifestyles similar to those filled by a variety of rodents and small insectivores in other places. In Australia, placentals may never have arrived, or at a very early date, were outcompeted by marsupials, at which point Australia separated, safeguarding the marsupials from further placental colonization and leaving them to dominate the mammalian fauna and evolve to fill a far greater range of ecological niches. But in all other places in the world, placentals became far more diverse after the dinosaur extinction, and eventually outcompeted and rendered extinct the marsupials in those parts.

The South American marsupials are all 'opossum'-types. The Australian marsupials include similar types called 'possums', but these are actually not closely related to the opossums of South America – with a single exception, a tiny opposum-like critter called the Monito del Monte that actually belongs with the Australians despite being in South America!

The Virginia opossum clearly belongs to the South American group, representing a recent extremely successful type that voyaged from that continent, after the formation of the Isthmus of Panama about 3 million years ago, into the north. This re-established marsupials in North America, where they had previously been extinct for many millions of years.

The reproduction of marsupials is weird. Marsupial females have two vaginas and two uteruses, and now you understand the scientific name for the Virginia opossum! The two vaginas fuse and open in a single tract, and sometimes a third canal called the median vagina develops through which they give birth. Most males have forked penises, one for each branch of the feminine vagina. The male penis is only used for reproduction, not for urination.

In this scheme, the reproduction of the Virginia opossum is not unusual. They can have two litters per year. The male has a gland on his chest that exudes a musky-smelling liquid at the start of the breeding season. He courts the female by making clicking sounds. Males may have multiple partners, and only the female is entrusted with caring for her young. She gives birth to typically 8-9 (but sometimes as many as 20) young after only 11 to 13 days. They're the size of a honey-bee at birth. Despite their undeveloped stage, they crawl up her fur from her median vagina to her pouch, which contains her teats, where they latch on and remain for about two months. Then they exit and climb up onto her back, where she carries them as you see in my picture. But sometimes they stay in their den while she goes out to forage. They gradually learn how to care for themselves and leave their mother aged four or five months. A great many young die before reaching adulthood – sadly, this is the case for many other marsupials. They are sexually mature at the age of six to eight months. They seldom live more than two years in the wild, but there are reports of captives living for ten years.

Possums are quite variable in size, adult males weighing from 0.8 to 6.4 kg/1.8-14 lbs and females 0.3-3.7 kg/0.7-8.1 lbs. They can thus reach the size of a large cat! Northern individuals tend to be larger than those from the hotter, southern regions. They can reach 1 m/yard in length including the tail, but the average is 72-76 cm/28"-30". They are 'conservative' in general build, meaning very similar to ancient mammals, even back to the time of the dinosaurs. This is why they look like rats – this is a very successful body shape that goes way back and still 'works' for a variety of not-closely-related critters. They have tiny brains – just one fifth the size of that of a raccoon, but that doesn't necessarily mean they're stupid. They have 50 teeth, which is more than any other American land mammal. They have five fingers and toes per hand and foot, and their big toes can oppose the others to grasp with, like our thumbs. The tail is prehensile and can grasp objects. They can and do use the tails for gathering nesting material, but do not sleep hanging from them. Only when young can they support their bodyweight from their tails, but just for a short while.

Another habit for which possums are famous for, is indeed real, is 'playing dead', which is even called 'playing possum'. They don't always do it. When threatened, their first response may be to try to run away, or climb into a tree. If this is not feasible, they may stand their ground and try to intimidate whatever is threatening them by opening their mouths to show their teeth, snapping, drooling, hissing, and raising their fur to seem bigger. Only if this doesn't work does a possum actually feign death. It drops down on its side, let its tongue loll out, reduces its heartbeat and breathing to where it's barely perceptible, clenches its feet, and releases a greenish, foul-smelling liquid. This not only simulates the stench of putrefaction, but in itself may repel a predator. Unfortunately, this tactic is no help against motor vehicles. . .

In its general lifestyle, a possum is a very versatile critter. Its natural habitat is open woodlands with accessible sources of drinking water, but it can adapt to many man-altered environments. It is largely nocturnal but can be active by day. It walks around its territory with a pacing gait – that means the left fore- and hindlegs move forward together at the same time, followed by the right fore- and hindlegs. Females carrying babies are slower and must spend more time foraging. Possums are not really adapted to withstand extreme cold, and make use of many holes or crevices, including in man-made structures, for shelter during cold times. They may den in holes up in trees. They don't hibernate. Sometimes they get frostbite on their naked ears, snouts or tails. Their food can be almost anything – fruits and nuts, eggs, small critters, and carrion. When they are attracted to roadkill, they may become so themselves. They also eat food associated with humans, such as discarded food in the garbage, pet food, bird seed, cultivated grains or crops, and poultry.

It's been said that possums combat Lyme Disease by consuming large numbers of ticks, which are the disease's carriers. But though studies show that possums may in captivity catch and eat large numbers of ticks that try to infest them, additional studies didn't support ticks as being an actual significant part of their diet.

Possums themselves are hunted by many animals. In their favour, they are immune to the venom of snakes from the viper family, such as rattlesnakes or copperheads. They likely benefit from the reduction in predators around human habitation, as well as taking advantage of food and housing opportunites. They're occasionally eaten by people, especially in the South of the USA, and there are even beliefs that their flesh and bones have medicinal properties. They're also hunted for their fur. They're sometimes persecuted for being nuisance animals. Yet, their adaptability and widespread occurrence, to the point where they're still expanding their range, should safeguard them against extinction, more than most other wild animals.

Willem

27.11.23 Front Page

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