Ivory Towers: How a good meal can save the life of a praying mantis

'COURTSHIP, mating behaviour and sexual cannibalism in the praying mantis, Sphodromantis lineola,' is the title of a short paper in Animal Behaviour (1994, vol 47, 739-41) which challenges beliefs about the link between sex and cannibalism, writes William Hartston. When a female praying mantis eats her mate, it is not through sexual frenzy, but through hunger.

That is the principal conclusion of a set of experiments by Suzanne Kynaston, Peter Mill and Paul McErlain-Ward at Leeds University, where mantises, male and female, hungry and sated, virgin and experienced, were watched and recorded as they went about their business.

The belief that females ate their mates after copulating had been supported by evidence that 'decapitation does remove cephalic neural inhibition of copulatory motor patterns'. So it's off with his head if the lady wants a good time. A good post-coital meal will also benefit the health of the female and her offspring.

For that reason, being eaten may also be good for the male (genetically speaking), although the researchers point out: 'Males will benefit only if mating opportunities are rare, or if females mate only once.' Generally, it seems that 'males may be better served by surviving copulation and finding further mating opportunities'.

To find out what was really going on, they introduced single males into a tank containing one female which had either been fed as much as it desired, or been starved for four days. 'Behaviour was videotaped for later analysis; recording commenced when males fixated on females and terminated at completion of copulation or cannibalism.'

While most males performed a courtship display, others wisely approached from the rear (the 'sneak approach') and leapt on females' backs from a distance of 2-8cm. No well-fed female ate any of her mates, but only one male survived an encounter with a starved female.

'Experiments using food-deprived females were restricted as it became clear that the males were unlikely to survive.' Worse still, only one of the eaten males achieved copulation: 'In all other cases the female held the male in such a position as to preclude this.

'Sexual cannibalism in Sphodromantis lineola thus appears to be the product of female hunger; given this propensity in the female, mating has considerable attendant risks for males.' Especially in the wild, where food is generally in short supply.