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NOT all hunters stalk or chase their prey: some lie in wait. For them, being able to blend inconspicuously into the background is crucial. It gains them that vital fraction of a second in attacking prey — time that can make all the difference between a meal and an empty stomach.
This strategy is taken to the extremes by the Namib desert adder. Not only does it match almost perfectly the colour of its surroundings, but it also buries itself in the sand with only its eyes exposed. Even so, the adder may have a long wait in this sparsely populated area. Its chances could have been better if it were able to wait in a spot that its prey found particularly attractive — a technique that is used by flower, or crab, spiders. |
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| Females of many species seek the strongest
and the fittest male to mate with, so that their
offspring will have a good chance in life. But females of
some species cannot do this, either because they cannot
distinguish between good and poor males or because they
have little control over who mates with them. Female European adders, however, seem to have found a solution to the problem. They emerge from hibernation in early spring with fully formed eggs waiting to be fertilised, and release an irresistible scent to advertise their availability to male adders. During a study of adders in southern Sweden, female adders were observed mating with several different males. After the offspring were born, NDA tests were used to discover the identity of the fathers. It revealed that females who had the most partners had produced the greatest number of surviving offspring. This could have been a result of the keen competition between the various sperms in a female’s reproductive tracts. This, in turn, meant that a larger proportion of her eggs had been fertilised by genetically fitter males. When the mating season begins in April, some male European adders defend their patches of ground against other males. Most of the fighting is symbolic — the adversaries rear up against one another, each striving to press the other to the ground. Once the weaker snake has been forced to yield, it will leave the scene. No biting occurs — venom is kept for the business of killing prey. Often the sight of writhing, entwined male snakes has been mistaken for a courting ritual. As prelude to mating, a male adder runs his tongue along the female’s back and vibrates his body against hers. After mating, the female stores the sperm for 60 days before fertilising her eggs. Then after about another 60 days, her 6-20 young, which are each about seven inches long are born, complete with fangs and venom. In the case of red-sided garters, the situation is slightly different. With the advent of the Manitoban spring, thousands of garter males emerge from their hibernation pits in the rocks where they have spent the past six months. Though they have not eaten anything in that time, they make no effort to disperse and find a meal. Instead, they remain by the pits waiting for the females to emerge. Because the females come out singly, or in small groups, they are outnumbered by the waiting males by something like 5000 to 1. As she appears, each female exudes a scent that signals her readiness to mate. Each male within range picks up the molecules on his flickering, forked tongue, which transfers them to the receptive Jacobson’s organ in the roof of the snake’s mouth. This triggers the male sexual response and, in moments, a lone female can find herself at the centre of a pile of perhaps a hundred writhing males, tying themselves into a living ball, and all trying to get into position to mate with her. Only one of the suitors is successful, for when he has mated, he leaves a cement-like secretion that bars other males from penetrating the female. At the same time, she switches off her scent signal and the males depart in search of more receptive mates. The large number of suitors guarantees that every female has been impregnated within 30 minutes of emerging from the pit. This in turn ensures that the young are born before the northern winter and the next hibernation. |
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The simplest way of blending into the
background is camouflage — colouring and patterning
that conceals body shape. This is the method employed by
the South African horned adder, a snake that lies almost
invisible among the rocks as it waits for a suitable meal
to come along.