Diving beetle's sticky underwater mating secret

Video shot through the lens of a microscope reveals how the beetles' remarkably evolved legs stick to a female's body

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Scientists in Taiwan have revealed how a diving beetle hangs on to its mate underwater.

The micro-scale study revealed how bristles on male beetles' legs attach to females with tiny suckers or spatulas.

As well as shedding light on evolution at a minute scale, understanding this could inspire the design of devices for underwater attachment in engineering.

The results are published in the Royal Society journal Interface.

Diving beetle Specialised bristles on the diving beetle's forelegs allow him to hold on to a female underwater

The team, led by Dr Kai-Jung Chi from National Chung Hsing University in Taiwan, directly measured the gripping force of the "attachment devices" on the leg bristles of two diving beetle species.

The efficiency of this underwater attachment, Dr Chi explained, was vital for the survival of the beetle.

"Once mating completes, the male has to separate from the female to get oxygen from the water surface or otherwise it may die," she told BBC News.

"In other words, the male beetles have to attach to and detach from the female as quickly as possible."

Microscopic plunger

Microscopic images revealed that one of the species Dr Chi and her team studied - a more primitive diving beetle - has a spatula-like attachment.

Another species the team examined has evolved circular suckers on the end of each leg bristle, which look like a microscopic plungers.

Micrograph of diving beetle leg bristles Microscopic images revealed how primitive "spatula-shaped" bristles worked

While these tiny plungers created a stronger attachment, the more primitive bristles had some sticky, aquatic secrets.

Tiny channels on the hairs in the more primitive beetle appear to "leak" liquid, which acts as a glue.

And, as grisly as it may sound, the fact that these bristles form a weaker attachment and can move around on the female's body more freely means that the male beetle is able to "resist the female's erratic swimming movements", which she may employ to dislodge an unwanted suitor.

Micrograph of diving beetle leg bristles "More highly evolved" suction cup bristles form a stronger attachment to the female beetle's body

"The sucker hairs work as typical suction cups," Dr Chi explained, "whereas the spatula hairs perform like a quick, controllable, and reversible underwater tape."

And all of this detailed insight into aquatic copulation may inspire a future underwater Velcro.

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