Monday 19 November, 2001
Male snakes con females to keep warm
Male snakes imitate females to keep warm and hide from predators.
This discovery, published in the latest edition of the journal Nature suggests that there may be many more reasons for male animals to act like females than previously thought. BBC Science investigates.
Strategies
Right across the world, there are many examples of females behaving like males and males acting like females in order to obtain some kind of an advantage over their peers.
Males in some species are known to pretend to be females so they avoid being preyed upon by larger males, or to allow them to mate with unsuspecting females.
But now a group of scientists from Australia and the United States believe they've found yet another reason for male animals to mimic females - survival after the winter.
Winter
Researchers at the University of Sydney and Oregon State University have been studying a type of male garter snake from Canada. The snake measures approximately 80 cm in length and feeds on a variety of worms, fish and frogs.
| 'In harsh winters, garter snakes congregate in underground dens, beneath the frostline, to hibernate. One den may contain as many as 50,000 snakes.' |
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In the spring, when they emerge months later, they are cold, weak and very slow. In order to survive they need to warm up as quickly as possible and get moving.
Scientists now believe that when the snake comes out of hibernation, it produces pheromones – a naturally occurring chemical substance which makes it smell like a female.
When the males seek the females they form mating balls (or concentrations), which can include as many as 100 males. By pretending to be a female, the weak male attracts many other males who pile on top of it.
The group of snakes transfers its heat onto the weak snake while at the same time protecting it from attacks by crows.
The researchers established that those snakes which behaved like females (she-males) warmed up much more quickly than those males who carried on smelling and acting as males.
Attracting the courtship of vast numbers of males only lasts a few days though. The journal Nature reports:
| '... She-maleness has since been shown to be a transitory phase that is restricted to the first day or two after a male first emerges from his eight-month hibernation.' |
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The researchers in Sydney and the US say that although female mimicry is often assumed to give males mating advantages, simpler explanations – such as hiding from predators - should be considered when trying to explain the phenomenon.
Tricks with pheromones
Other species also secrete pheromones and scientists are increasingly studying these chemicals for the key roles they play in recognition and reproduction in the natural world.
The larvae of a species of tiny beetle gather together in their hundreds and form a mass that manages to resemble a female bee.
When a male bee tries to mate with this “female bee”, the larvae grab onto his chest hair and wait. When the male bee finally finds a real female to mate with, the larvae jump onto the female.
They are then transported into the hives, where they act as predators - eating the eggs and the food provided for the young bees.
The female bolas spider also practices mimicry through its skillful use of pheromones production.
Like many other spiders, the bolas spider produces silk. Unlike others though it does not create webs to trap its prey. Instead it produces one strand of silk; suspended at its tip is a sticky ball of glue.
The ball, or bolas, contains pheromones that resemble the scent produced by a species of female moth. The scent of the chemical is used to lure the male moth into believing that there are females nearby.
Once the male approaches, the spider swings the ball and aims it at the moth. If the ball with the glue touches its target, the moth is doomed.
|  |  | | | Human pheromones |  |
| | The chemical messengers known as pheromones – both colourless and odourless – are thought to affect behaviour in both animals and human beings.
Scientists believe pheromones may help fool men into thinking plain women are more attractive than they actually are.
Professor Karl Grammer from the University of Vienna thinks the pheromone warfare probably evolved millions of years ago to help plain women find a mate and stop very attractive women from being pestered.
Professor Grammer also believes the contraceptive pill could stop a woman secreting pheromones and undermine her ability to pick up the right chemical signals from men.
She could even chose a partner with whom she may not be able to produce a child.
Other scientists say pheromones are only one ingredient of sexual attraction. They do not affect a person’s perception of another individual’s intelligence or confidence. |
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