Country Ecology: Opossum
(Reprinted from above link)
When I was a kid in Maryland, one of the common things to experience was the family dog bringing home a litter of young opossums. These little marsupials were not going to do well with our desperate husbandry, but we always tried anyway. Cottontail rabbit litters were next on the agenda, but if you had a golden retriever, you were going to receive lots of box turtles and wildlife that you didn’t need from the nearby Maryland woodlands.
For many a year since that Maryland youth, naturalists and wildlife managers in our New England region said you would never see such a southern species as an opossum in New Hampshire; but that has come to pass. The reason for their rationale was that these primitive creatures would not survive frost bite in their non-furred faces and hoary, scaly tails, and therefore not extend their range into New England after some attempts.
This species, still described as “neotropical” by some sources, has been moving north since at least the 1950s. In many parts of the Northeast, opossums (frequently shortened to “’possums”) are as familiar as squirrels. Yet, this is no mere rodent, and it has been around humans since prehistoric times, with its fossil record stating it was back there just after the extinction of the dinosaurs. The Isthmus of Panama rejoining North and South America allowed the odd beast to populate the southeastern United States, and they have continued north ever since.
As described in a magazine article, possums are the only marsupials native to North America. Despite appearances, they are closer kin to wombats and kangaroos than rats. Marsupials branched off of the main mammalian family tree long ago, and many of the traits they exhibit offer a window into what ancient mammals very probably were like. Many of these differences relate to reproduction.
All marsupials have pouches. They need these because they are not, like most mammals, placental. Their young spend barely any time developing in the mother’s body. They’re born in a near-fetal state, and the tiny, naked and blind young must make a scramble to the pouch where they can complete their development in relative safety. They then must soon suck on their mother’s teats, which are not inside that warm convenient pouch.
The article goes on to say, “Newborn possums are born only the size of honeybees and many don’t survive the trip to their mother’s fur-lined pouch. Those that do must locate one of 13 nipples, arrayed in a circle with one in the middle. As soon as a baby possum starts to suckle, the nipple swells in its mouth, effectively trapping it in place until it has grown big enough to free itself.
Once out of the pouch, the baby possum, along with its litter-mates, will hitch a ride by clinging to its mother’s back.” And that’s what a native son of Maryland soon observes about them.
Playing possum can get this cat-sized animal run over on the highway where it scavenges road kills. The opossum also defecates and exudes a noxious oil green slim from its anal glands in its feigned death. The act may go on for hours.
It’s perhaps little wonder that the possum should be so good at imitating death, because death lurks around every corner for this species. Due to heavy predation, and a predilection for becoming a dumb road kill, possums typically live only a measly two years in the wild, and even those living in captivity succumb to old age quickly.
And this death rate is despite a few startling immunities. Possums are highly resistant to pit viper snakes’ (e.g. copperhead, water moccasin) venom. Research suggests that possums — which will eat rattlesnakes with their spiky teeth, among many other things — are locked in an evolutionary arms race where they are constantly developing new ways to combat these dangerous snakes’ venom. They’re also highly resistant to rabies, likely as a result of a slightly lower body temperature that makes it difficult for the virus to thrive. You begin to respect these smelly dudes.
They also function as “tick vacuums.” A possum trundling through the undergrowth accumulates a large collection of ticks, but possums are such fastidious groomers that ticks which latch onto them are as good as dead. A dense possum population may even help reduce the prevalence of Lyme disease.
White-footed mice would keep an average of 50 to 100 ticks to each animal’s neck to repletion, but opossums eat the ticks they are carrying before they can fall off as part of their cycle. Opossums were unlikely to get infected by the deer ticks they were carrying around to move these pests to other small animal life. Only 3.5 percent of ticks on opossums survived to drop off. And the opossums, all the while are grooming and chewing.