A male redback spider climbs on the back of a female before mating at Taronga Zoo. Credit:Reuters The redback, Latrodectus hasselti, is usually described as monogynist, whereby the males mate just once. However, in this new research Biaggio and Sandomirsky found that 65 per cent of males had copulated with immature females. They also found that one-third of immature female redbacks carried sperm. They suggest that "immature-mating may be a widespread, previously unrecognised mating tactic". In other words, the males often mate first with an immature female before later mating with an adult female, which then eats them, in what biologists call copulatory cannibalism.

A redback spider. Helen Smith, an arachnologist at the Australian Museum, said the findings were "pretty amazing". Explaining their mating behaviour, she said that male redbacks would somersault while copulating and "voluntarily put their abdomen into the jaws of the female". Dr Smith said this slowed the mating process down "by giving her something to chew on". A slower mating process would increase the male's chance of paternity. The paper by Biaggio and Sandomirsky, published on Wednesday in The Royal Society's Biology Letters, says that "copulatory somersaults and sexual cannibalism were rare" between adult male and immature female redbacks.

And the process by which the males access the immature female's genitalia is not straightforward. As they grow, spiders moult their exoskeleton. In the last phase of this process, the female genitals develop while still covered by the exoskeleton, so the males must break this layer. They do this with their mouths. "Observed contact between the males' mouthparts and the raise epigynal area ... suggests males opened the female's cuticle with their fangs and access the copulatory openings," the study says. To further enhance paternity, earlier studies show that the tip of the male secondary mating organ - the pedipalp - can break off, plugging the spermatheca and blocking future inseminations.

It's a tough world for redbacks. So why don't the immature females eat the males? Dr Smith said it was likely the process happened when the female was about to start her final moult and lacked the energy to do so. But the sexual intrigue of the spiders doesn't end there. The adult males don't waste time with courtship rituals with the immature females. Studies have shown in the Latrodectus genus of widow spider (that includes the redback) more than "two hours of vibratory courtship precedes mating". The male spends time sending signals of intent along the web. In fact, the longer the male spends on the courtship before mating, the lower the chance of being cannibalised.

But with immature females, the males send no such signals. I'd like to say there is a lesson in all of this for us, but there isn't. Anthropomorphism is a futile pursuit.