Why do women live longer than men? Scientists (and Buzzfeed listicles) have given the question plenty of scrutiny over the years, but when it comes to garter snakes in Canada, the answer really is a classic: sex.

Among red-sided garter snakes in Manitoba, some of the most northern-dwelling reptiles in the world, the sexes are not made equal. Compared with females, males reach maturity earlier, but tend to stay smaller – and they die earlier, too. Based on a new study of the snakes' DNA, it looks like the sex-obsessed males simply aren't taking great care of themselves.

For eight months of the year, the garter snakes gather together in caves, fissures or other available dens, and wait out the long, cold Canadian winter. Then, when spring comes along, the snakes emerge in a sight that would give Indiana Jones nightmares: masses of hundreds upon hundreds of writhing, wriggling snakes.

A female (she's the large red-sided garter snake) being pursued by smaller male snakes during the mating season in North America. Image: Christopher R Friesen

Indy wouldn't have much to worry about here, though. These garter snakes are totally harmless (unless you're a frog). Besides, they have other things on their minds. This spring emergence is the main opportunity for snakes to get busy. Multitudes of males scramble all over each other to gain access to females, fuelled by overactive hormones that shuttle their internal energy towards courtship and mating (it's kind of like high school).

But a garter snake's experience of this breeding season craziness depends largely on which sex it belongs to, explains Christopher Friesen of the University of Sydney, lead author on the new study.

"Although we believe that all females mate every year," he says, "they only stay at the den sites, where mating takes place, for a short period of one to three days – much less than males, who remain at least a week and up to 21 days."

In the breeding season, these snakes gather in mating masses as they emerge from hibernation. Image: Christopher R Friesen

This extended mating period is so intense for the males that they don't even eat, and some will famously resort to trickery such as impersonating females to distract their competitors. All this high-stakes rivalry takes up precious energy, of course – so is this the cause of the males' quicker deterioration with old age? 

To find out if males really do break down faster than females, the researches examined the snakes' DNA, specifically looking at structures called telomeres. These long stretches of DNA that sit at the ends of chromosomes become frayed every time DNA replicates. They protect the important parts of the DNA from damage over time, but they become shorter with age and stress.

In the garter snakes, the condition of the telomeres mirrors the condition of the animals' bodies – and sure enough, both body and genes deteriorate quicker in males than in females. It seems all that energy spent on high-intensity mating bouts takes away from energy that could otherwise be redirected towards processes that protect cells and DNA.

The females, meanwhile, seem to take much better care of themselves, and once they get out from under the giant pile of sex-crazed males, they have a much more relaxed spring experience. This strategy allows them to make the most of their short summer hunting frogs and developing their young. The baby snakes emerge live from mom, who leaves them to their own devices as winter approaches once again.

According to Friesen, a healthy body and bountiful hunting allows the females to build up fat and energy for future reproduction. They're even able to hold onto a mate's sperm until they're ready to use it. "Our previous research has shown that females can store sperm for up to 15 months or more before she uses the sperm to fertilise her eggs!"


Top header image: Daniel Arndt/Flickr

This new study was published in Proceedings of the Royal Society B.