Suicide song: cicada's sex racket risks death for shot at love

THE male cicada's mating call is as romantic as an AC/DC concert. It's more a slap in the face than sweet serenade. This summer's bumper crop is so overwhelming some National Parks rangers have taken to wearing earplugs.

The insect's racket - as lovely as hugging a jackhammer or jet engine - turns the head of friend and foe alike. The louder it bellows, the more potential partners and predators it attracts.

''It's a pretty risky business sitting up in a tree calling for a mate,'' says Australian Museum entomologist Dave Britton.

Cicadas are the suicidal lovers of the insect world, risking death for several weeks of singing and sex. ''It's a compromise: like a lot of sexual behaviour in animals, the males perform dangerous behaviour to advertise they are strong and virile and represent the best chance of producing lots of children,'' Dr Britton says.

CICADAS FEELING CHIRPY AND OUT ON THE TOWN

''But you are basically training up a whole bunch of predators, such as birds and wasps, to track you down and eat you, so it is pretty suicidal.''

Cicadas spend most of their life underground before emerging from the soil for their final few weeks to mate. Some cicadas in North America have employed mathematics to overcome the perils of love. Periodic cicadas have evolved to emerge only at prime number intervals - every 7 years, 13 years and 17 years - to evade predators with shorter lives.

This love affair with prime numbers - numbers that can be divided only by themselves and one - makes these cicadas relatively immune to predators with a two-, three-, four- or six-year life cycle. ''They are actually able to detect how many years they are underground from changes in the sap flow and temperature,'' Dr Britton says.

''It is really odd because people tend to think of insects as being basic robots but they are much more sophisticated.''

Unfortunately, Australian cicadas are less patient when it comes to partnering up. Cicadas such as green grocers, floury bakers and razor grinders are thought to emerge every four to six years, Dr Britton says.

This summer has delivered the largest number of cicadas along the east coast in years, presumably because of favourable breeding conditions between 2007 and 2009. There is, at least, safety in numbers - even if they are not prime ones. The racket generated by a gang of cicadas might deter predators.

Alternatively, emerging en masse can sate the appetite of the most hungry foe. ''A lot of cicadas end up surviving because birds become so sick of eating them,'' Dr Britton says.

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