Adders filmed in Northumberland for BBC series Wild Isles with Sir David Attenborough

A pair of male adders ‘dancing’, which is in fact a battle to subdue their opponent. Picture: BBC

The males are dragged around by their penises by the females, staying bound together by dozens of penis barbs that have evolved for this purpose

Producer Nicholas Gates said: “Filming this number of adders mating has never been filmed before; in some of our mating balls we filmed six adders, a behaviour that is exceptionally rare to see, let alone to film.

“Across the three weeks filming for this sequence, we found at least 52 different individual adders, guided by the expert identification skills of herpetologist Nigel Hand.

"By closely and carefully following the individuals as they emerged from hibernation, and particularly by following the males which sometimes moved hundreds of metres following the scent of a female, we were able to pinpoint the exact locations where mating was taking place to capture the extraordinary footage of this moment.

"We had a camera team of three people, and an additional field team of four people, who were all assigned spotting duties to follow individual adders that we expected to mate or battle.

"Everyone was in radio communication ensuring that as soon as any behaviour looked likely, the nearest member of the camera team could be called in to quickly relocate and film the action.”

Camerawoman Katie Mayhew added: “To get the super low angle shots at the same level as the snakes, we underslung the rig so the camera and lens could slide almost touching the floor - at some points I even had snakes on the equipment and on my boots!

"Once I was set up, I could then operate the slider a few meters away so I could give the snakes some space to behave naturally.

"As soon as the mating behaviour started, I jumped quickly onto another camera set up, which was a tripod and a long lens, so I could follow a mating pair easier and help capture some of the more intimate behaviours, like the male head tapping the female.

"These truly are stunning creatures and I really enjoyed spending so much time filming and getting to know and understand the species better.”

It airs on BBC One and iPlayer on Sunday, March 26 at 7pm.