On cannibalism and spider bondage

Tips for males to avoid being eaten during sex

Redback male cautiously approaching a female. Photo:Daily Telegraph

 “Love hurts”, according to Roy Orbison, Aerosmith, and too many others to list.

A clichéd metaphor for us – but in some species, it is a bit too true for comfort.

One of the weirdest observations in nature, for example, has to be the sexual behaviour of the Australian redback spider.

In the midst of mating (which, by the way, happens between organs on the male’s mouth and the female’s belly, as in all spiders) the male redback spider does a spectacular reverse somersault, using his mouth-based genitals as a pivot, and impales himself on the female’s jaws (see this video from about the 2:00 mark).  While he finishes what a man has to do, the female sucks his body dry.  Up to seven out of ten males die this way, during sex.

Being cannibalized isn’t so bad

Praying mantis female chews off the head of a male. Photo:Biozine

I would hope by now your scientist brain is screaming “WHY?!” Surely Darwin is turning in his grave?

Darwin would probably approve, as it happens.  Male redbacks that commit suicide in this fashion manage to mate for longer and fertilize more eggs than those that do not. And it’s not just redback males that are perfectly happy to lie back and think of Australia while being horribly eaten.

Cannibalized male Hierodula mantises can take comfort from the fact that their flesh-fed mates will have more babies than those of uneaten males.

A male Nephila spider can feel assured that his shriveled, torn-off genitals will stay attached to the female for hours afterwards, repelling other males.

As if this were nothing, Argiope male spiders spontaneously die in the act of sex, leaving their dead body as an obstacle to future amorous males. Face it, removing the half-eaten corpse of a previous lover is not really a turn-on.

50 reasons to eat your lover

What does the cannibal female get out of it?  “Man-eater” females are not rare among arthropods – especially among praying mantises and spiders, whose females are often observed chowing down on hapless would-be hubbies.

In many cases, the hungrier a female is, the more she is likely to eat the male, even though males often make poor-quality meals.

By attacking everybody, female orb spiders can weed out the weaklings and only mate with the strongest males.

Female wolf spiders cannibalize no-hoper males whose attention just attracts predators.

But why are mantises and spiders special? Shawn Wilder and colleagues have found that size difference is one key – the smaller males are relative to females, the more likely they are to be gobbled up.  In mantises and spiders, females commonly dwarf males.

The self-preservation society

But not all males go quite so gently into that good night as do male redbacks.  Understandably, males of most species would rather not be cannibalized. And faint heart does not win fair lady. According to this recent study, male mantises are more willing to risk being killed and eaten if females are scarce in the environment.

But a male on the pull can employ a number of tricks to avoid ending up on the menu.

Tenodera mantises have an obvious tip: only chat up a cannibal when she has just eaten.

Male Pisaura spiders go one further and offer her dinner first before trying it on (although occasionally the female still thirsts for blood, whereupon they feign death).

Pisaurina males tie females up before mating. Source:Bruce & Carico (1988)

For some male spiders the solution is to get kinky. The male Pisaurina spider ties his mate up in silk before sex, to make absolutely sure she can’t eat him.

Male Agelenopsis are into asphyxiation games – the male gasses the female with a narcotic pheromone, ensuring she is too groggy to attack.

Some males have an insurance policy. In the 1930s it was discovered that male praying mantises have a second, extremely horny brain in their genitals that takes over if the main brain is eaten. As Greg Holwell explained at a recent conference, this brain is capable of steering the genitals to the appropriate bits of the female even when the male is nothing but a disembodied abdomen. As soon as the female eats the male’s brain, the sex-crazed backup takes over and immediately lunges for her privates.

The courses of true love

Finally, some males have turned the tables and indulge in a little role reversal.  According to this study, if a female wolf spider’s looks and sexual history are not up to scratch, it is she that is apt to become lunch for the hungry male.

The take-home message is this: when a pop star warbles your way about the pain of love, at least be glad you’re not an spider or a mantis.

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