Genetics triggers male black widows to blackflip into death, study finds

A wild widow spider behavior involving a backflip into death during sex has a simple genetic explanation, new research finds.

Male redback spiders ( Latrodectus hasselti ) — Australia's version of black widows — flip into females' fangs while mating in order to make sex last longer.

They also constrict their abdomens — a maneuver that seems to help them survive the experience of being eaten alive long enough to finish transferring their sperm.

Then, they break off their sperm-transferring organs, known as pedipalps, into the females like a cork on a bottle, which prevents other males from inseminating them.

Intriguingly, a close New Zealand cousin of the redback, the katipō ( Latrodectus katipo ), doesn't do any of this. ‪There are no backflips and no cannibalism — just a respectful courtship dance and a polite parting of ways afterward.

That difference offered researchers an opportunity to understand the genetics of the more gymnastic mating behavior.

"What makes this system so intriguing is the fact that we are dealing with two species here, which are very closely related," Kardelen Özgün Uludağ , a doctoral student of behavioral biology at the University of Hamburg in Germany, told Live Science in an email.

These two species may have separated less than 100,000 years ago, but they still show entirely different behavior and observable traits.

"This is very uncommon in animals," she said.

To figure out the genetic basis of this behavioral schism, Uludağ and her colleagues first exposed katipō females to redback males so that they would mate.

The two are closely related enough to yield hybrid offspring.

The researchers then crossbred hybrid females with either male redbacks or male katipō spiders.

This led to mixed-genetic males. (The researchers couldn't mate katipō males with redback females in the first place because redback females will eat katipōs instead of mating with them.) A female hybrid Katipō-redback spider.

This spider is the daughter of a first-generation hybrid Katipō-redback spider that mated with a Katipō male. (Image credit: Miriam Scriba) The researchers took these hybrid males and paired them with katipō females so they could watch their mating behavior without any of them getting eaten.