I promised a post on this unusual encounter last weekend at Pocosin Lakes so here goes (I should warn you this may be for mature audiences only)…I started my morning with a sighting of a pair of Virginia Opossums (aka ‘possums) mating at the edge of a field just after sunrise. I have been “fortunate” enough to run across mating ‘possums three times in my woods wanderings over the years and each time noticed a behavior that I had once read about and to this day still don’t quite understand – but more about that in a second.
Possums are definitely unusual mammals. Here are a few reasons why:
- They are North America’s only marsupial (pouched mammal, like Kangaroos)
- When confronted by a dog or potential predator they often feign death (play ‘possum)
- Their skull contains the most teeth or any North American land mammal (50)
- They appear immune to the venom of pit vipers like rattlesnakes and copperheads
- Opossums, for their size, are one of the shortest-lived animals in the world with few in the wild making it into their second year
- They have a notoriously tough time crossing roads (related to above?)
But their uniqueness is most noticeable when it comes to their unusual reproductive habits. Female opossums generally raise two litters per year with the breeding season running from January through early summer. Males are known to make a peculiar constant clicking noise as they amble in pursuit of females. Females are only receptive for a short period of time and will hiss, click their teeth and threaten biting if not ready. When at last he does find a receptive female, he bites the fur on her neck and then climbs on her back (you can see wet matted fur on the top of the females’ neck if you look closely at one of these pictures).
He then grasps her hind legs with his hind feet and then they both roll over on their right sides to copulate (this is the behavior I have witnessed all three times I have seen it – the “right side roll”). Studies have shown (I just love it when this phrase is used…who studied this and why?) that if for some reason the mating pair remains upright or falls over to the left, mating is less likely to be successful. Apparently a researcher in the 1950’s failed to find sperm in the female’s genital tract after the pair remained upright or fell to the left…go figure. Copulation lasts 20-30 minutes.
There are a few other oddities about ‘possum mating that have led to some interesting folklore. Turns out the male ‘possum has a bifurcate (forked) penis. Since early observers could not find a corresponding dual opening in the female they deduced that male ‘possums must mate with a female in her nostrils and she impregnates herself with a sneeze…this is actually part of mountain folklore. But, it turns out that the female has a double set of everything as well. And even though male opossums deliver a low sperm count (~3 million sperm compared to a male rabbit that inseminates a female with ~150 million sperm), the sperm are remarkably efficient. They, too, are paired. That’s right, ‘possum sperm pair up by sort of fusing their “heads” together then beating their tails together, making them far more efficient at reaching their goal. Another go figure.
All of this rather unusual reproductive ability naturally leads to an unusual birth, with baby opossums being born a scant 12-13 days after their parents mate. The bean-sized “embryos” then must crawl from the birth canal to the mother’s pouch, where they will remain for about two months as they develop into something that looks more like a ‘possum baby.
So, the next time you see one of those “grinning ‘possums”, think about all the amazing traits that go into making them one of our more endearing woodland critters.
Two wonderful references provided much of the information related here:
THE OPOSSUM: ITS AMAZING STORY
By William J. Krause and Winifred A. Krause
Published by the Department of Pathology and Anatomical Sciences, School of Medicine, University of Missouri, Columbia, Missouri (available online as a pdf)
Advanced ‘Possumology in
Wildwoods Wisdom, Encounters with the Natural World
By Doug Elliott