You Are Not Ready For The Mating Ritual Of The World's Biggest Slug

This Valentine's, say it with slime.


Rachael Funnell


Rachael Funnell

Writer & Senior Digital Producer

Rachael is a writer and digital content producer at IFLScience with a Zoology degree from the University of Southampton, UK, and a nose for novelty animal stories.

Writer & Senior Digital Producer

black-ash slug mating

Is that an ornate piece of glassware, or are two slugs just happy to see each other? Image credit: BBC Wild Isles screengrab, Silverback Films

Love-making in the animal kingdom comes in all shapes, sizes and confusing choreography, but for all of its weirdness it’s hard to imagine that there’s much left out there to surprise one of humankind’s most famous naturalists, David Attenborough. Remarkably, the presenter was still taken aback when a new series from the BBC brought to his attention the mating sequence of a pair of slugs whose reproduction looks like something from another planet. In fact, it took place in the UK.

Wild Isles is the name of the latest release from Attenborough in association with the BBC and Silverback Films, and it does something that his wildlife documentaries have never done before in turning the camera to UK wildlife. You could be forgiven for thinking that means there’s nothing much but pigeons and a few foxes to look at, but there again you would be wrong.


The series really puts the “wild” in the British Isles in bringing to the forefront some of the country’s most peculiar, dramatic and rare wildlife. As a special Valentine’s treat, they’ve released a romantic sequence between two ash-black slugs (Limax cinereoniger).

As the largest land slugs in the world, ash-blacks stretch to up to 30 centimeters (12 inches) and love a good ancient wet woodland. A memorable sequence from the new series follows one slug on its hunt for a mate as it leaves behind an alluring chemically-laced slime trail.

They start off by nuzzling, nothing too strange there. But then something... surprising happens.

The main event sees them dangle on a slimy tether while their penises (that are as long as their bodies) protrude and intertwine into a very alien arrangement that looks a little like ornate glasswork. Once the sperm exchange is complete, the slugs are done with one another, and a quick plummet to the ground marks a swift end to their romance.


And you thought phubbing was bad.

Wild Isles will air on BBC One this spring.


  • tag
  • animals,

  • mating,

  • animal behavior,

  • wildlife,

  • mating behavior,

  • slug,

  • documentaries,

  • slugs,

  • nature documentary