Male Redback Spiders Perform a Self-Sacrificial Somersault to Boost Reproductive Success

Male redback spiders (Latrodectus hasselti), one of two monogynous widow species, flip their abdomen into a female’s mouthparts during copulation. The maneuver, described as a “self-sacrificial somersault,” allows the male to continue pumping sperm while making it harder for the female to seize his abdomen, thereby increasing the chance of surviving the first mating. Researchers note that males aim to inseminate both of the female’s separate sperm storage organs, which maximises the proportion of offspring sired by a single male.

Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?

A German team published a study in *Biology Letters* that bred female katipo spiders (Latrodectus katipo) with male redbacks to trace inheritance of the somersault. Approximately 50 % of third-generation offspring displayed the behavior, leading the authors to link it to a specific region on the X chromosome. The finding suggests that a complex phenotype can arise from relatively few genetic changes.

Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?

Field observations by Cor Vink at Lincoln University have documented natural interbreeding between invasive redbacks and the endemic katipo. Vink warns that such hybridisation could threaten the protected katipo population, which diverged from redbacks roughly 100,000 years ago. The loss of the somersault trait in katipo over 100,000–200,000 years underscores the rapid evolutionary shift observed in redbacks.

Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?

Kardelen Özgün Uludag of the University of Hamburg, the study’s first author, emphasized that the behavior likely evolved to ensure a male can plug both female sperm storage organs, reducing the chance that a rival male will sire half of the brood. Vink described the paper as “elegant” and highlighted its relevance for managing redback-katipo hybridisation in New Zealand.

Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?

• “He’s pumping sperm, he flips his abdomen right over into her mouthparts and then he constricts his abdomen … to make it hard for the female to get a purchase on his abdomen. That lets him survive the first mating,” — Cor Vink, an associate professor and spider expert at Lincoln University in New Zealand

Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?

• “Ideally, males should mate with the same female two times because females have two separate sperm storage organs,” — Kardelen

Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?

• “In the katipo, the male inseminates the female and runs off the web – that’s the same for most widow spiders,” — Cor Vink, an associate professor and spider expert at Lincoln University in New Zealand

Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?

• “Our work shows that this highly complex cannibalistic behaviour can evolve rapidly, with very few genetic changes,” — Uludag, of the University of Hamburg, the study’s first author

Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?

• “It’s really neat that they’ve lost this behaviour in 100,000 to 200,000 years,” — Cor Vink, an associate professor and spider expert at Lincoln University in New Zealand

Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?