Genetic basis of male redback spider's self-sacrificial mating behavior
Consensus Summary
Researchers from the University of Hamburg discovered that male redback spiders' self-sacrificial somersault during mating is controlled by a single gene on the X chromosome. By breeding male redbacks with female katipō—a non-cannibalistic New Zealand relative—they found that roughly half of the hybrid offspring inherited the somersaulting behavior. This trait, absent in katipō, evolved independently from the abdominal constriction tactic used to delay cannibalism. The study, published in 2026, highlights how quickly complex behaviors can evolve or disappear over 100,000 to 200,000 years. In New Zealand, invasive redbacks threaten native katipō through predation and hybridization, raising conservation concerns. Both species require antivenom for bites, though no deaths have been recorded since the 1960s for redbacks or centuries for katipō.
✓ Verified by 2+ sources
Key details reported by multiple sources:
- Male redback spiders perform a 'self-sacrificial somersault' during mating, flipping their abdomen into the female's jaws to delay cannibalism while transferring sperm.
- The somersaulting behavior is linked to a specific location on the spider’s X chromosome, as shown by breeding experiments where ~50% of third-generation hybrids (male redback × female katipō) displayed the trait.
- Katipō spiders diverged genetically from redbacks approximately 100,000 years ago and no longer exhibit the somersaulting behavior.
- Redback spiders are monogynous, meaning males typically mate with a single female, while katipō males mate multiple times.
- Researchers analyzed 104 mating rituals to study the somersault and abdominal constriction behaviors in hybrid spiders.
Points of Difference
Details reported by only one source:
- The study was published in *Biology Letters* on Wednesday (no specific date provided, but publication year inferred as 2026).
- Cor Vink, an associate professor at Lincoln University, noted that interbreeding between redbacks and katipō in New Zealand could threaten the native katipō species.
- The term 'widow' for these spiders is a misnomer, as only redbacks and brown widows exhibit male sacrificial behavior among the 31 species of widow spiders.
- The study referenced research by scientists at the University of Toronto documented in a 2010 video from ABC TV's *Catalyst* program.
- No deaths from redback bites have been recorded since the introduction of antivenom in the 1960s, and katipō bites have not caused deaths in centuries.
- Redback spiders are invasive in New Zealand, predating on native species like skinks and beetles, while also hybridizing with katipō.
- The abdominal constriction behavior (to delay cannibalism) was not as clearly inherited as the somersault, suggesting separate genetic origins.
Where the reporting differs
Details that conflict, or appear in only some outlets:
- The Guardian states katipō diverged from redbacks 'about 100,000 years ago,' while ABC specifies '100,000–200,000 years ago.'
- The Guardian mentions the study was published in *Biology Letters* on Wednesday, but ABC does not specify a publication date beyond referencing the journal.
Source Articles
Male redback spiders invite cannibalism through a ‘self-sacrificial somersault’ during sex – but why?
New research sheds light on the genetic basis of the venomous arachnid’s ‘weird mating behaviour’ Follow our Australia news live blog for latest updates Get our breaking news email , free app or daily news podcast If you think you’ve had a bad one-night stand, spare a thought for the male redback spider, whose sole reproductive partner eats him after sex. Male redbacks appear to invite this cannibalism through a “self-sacrificial somersault”, with new research shedding light on the genetic basis
Male redback's bizarre death somersault during sex is in its genes
Male redback spiders somersault onto the female's fangs while mating and are killed. Researchers cross-bred the Aussie spiders with their NZ cousins to find out why.
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