The practice of biting the male’s head off during sex has earned the female praying mantis the reputation of a femmes fatale but the true motive for such sexual cannibalism has remained in question.

A new study supports the female of the species’ deadly temptress tag by showing that males are more attracted to starving females, but they have to be tricked into it.

The end result is that the males are cheated in two ways: they are exposed to the very high risk of being eaten and there is little or no chance of them producing offspring with the low egg-producing females.

Even more surprisingly, research found that the hungriest females attracted more males than well-fed females, which the author suggests is achieved by the more desperate females releasing higher levels of pheromones (long-distance chemical signals).

Previously studies have suggested that sexual dishonesty is not a factor among praying mantises, with males shown to be completely disinterested in females in poor physical condition or with low fertility levels.

The author of the study, published in Proceedings of the Royal Society B, said it is the first empirical evidence of sexual deception by females using pheromones, and the first to support the long-held hypothesis of the villainous female.

Diets and dishonesty

Female false garden mantises (Pseudomantis albofimbriata) were split into four groups that were fed on different diets, good, medium, poor and very poor. Their diets ranged from three crickets being fed to the 'good' individuals three times a week, to those in the very poor group receiving just one cricket three times a week.

The feeding regimes lasted for six weeks to ensure that all of the females would have eggs in their ovaries when the experiment began. Those mantises that received more food improved both their physical condition and fertility.

This is the first evidence of the 'Femmes Fatale' hypothesis

When males were introduced, three-quarters of females attracted a mate. Apart from the females on the worst diet, the number of males attracted to females increased with the amount of food the females were fed, supporting the idea that the mantis’ mating system is generally honest, with females in the best condition and offering the highest levels of fertility giving off the strongest signals.

However females who were fed the least attracted more males than those in any other of the diet groups, despite being in the poorest state physically and having low levels of fertility.

Other research has shown that 90% of females fed on similarly low levels of food are likely to cannibalise males, only half of interactions result in sex and the females have very few eggs to fertilise.

“This is the first evidence of the Femme Fatale hypothesis and also only one of very few examples of intraspecific sexual deception in the animal world,” said Dr Katherine Barry, lead researcher from the Department of Biological Sciences at Macquarie University, Australia.

Easy meal

It has been shown that pheromone production can be costly to animals, adversely affecting chances of survival and future reproduction, but Dr Barry notes that starving females have much to gain from the act of deception. Eating just one male can enhance their body condition by around one-third and improve their fertility by about 40%.

“These females are investing a lot into signalling because the potential benefits are so high. My guess is that this is a short term strategy to try and get an easy meal,” Dr Barry explained.

“Although producing any kind of signal has some costs involved, it may be that chemical signals are relatively cheap compared to other types of signals. So maybe it’s easier for these females to invest in a few days of pheromones than investing in egg production?”

Dr Barry said she is yet to discover whether males have evolved any defence against these risky females.

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