Insect anchoring inspires better suction cups

Engineers are often seeking better methods to stick articles to surfaces, for applications such as picking delicate berries or ensuring that surgeons can grasp tissue during operations. A discovery by zoologists at Cambridge University may have potential to help solve these problems.

The researchers are studying an insect called the net-winged midge, members of a family known as Blephariceridae. These long legged insects, like many flies, have larvae which are aquatic, and have a particular trick: they can anchor themselves firmly to rocks in streams flowing as fast as 3m/s. They do this using suction cups on their underside. The Cambridge team, as they describe in BMC Zoology, have succeeded in imaging these suction cups in high detail, revealing how they work.

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The cups can stand up to any force below 600 times the larvae bodyweight, explained Victor Kang, a PhD student and first author of the paper. "The force of the river water where the larvae live is absolutely enormous, and they use their suction organs to attach themselves with incredible strength. If they let go they're instantly swept away," he said. "They aren't bothered at all by the extreme water speeds - we see them feeding and moving around in all directions."

Kang and his colleagues studied the midges in Alpine rivers near Innsbruck in Austria. Wading in up to their knees, they found it difficult to stand in the water, but the midge larvae were firmly anchored and grazing on rocks in the torrent. Using scanning electron microscopy, scanning confocal microscopy and x-ray computed micro-tomography, they obtained images of the larvae suction cups and discovered that the cups have a central piston, which is controlled by specific muscles. The cups also have a dense array of tiny hairs on their inner surface, which come into contact with the surface of the rock on which they wish to anchor. The piston then creates a tight seal and a strong vacuum to anchor the larva tightly onto the surface. When it needs to move, more muscles control a tiny slit on the suction disc, which pulls it open allowing the larva to detach. This is the first time such an active detachment mechanism has been seen in any biological system, the researchers state.

The study was led by Walter Federle, a specialist in comparative biomechanics, who is now working with colleagues at the Leibniz Institute of New Materials in Saarbrücken, Germany to develop bio-inspired suction cups. Unlike current suction cups, familiar to all of us for sticking things to clean glass or tiled surfaces, these would be able to stick firmly to rough or dirty surfaces, and attach or detach at will.

"These natural structures have been optimised through millions of years of evolution. We want to learn from them to create better engineered products," Federle said. "By understanding how the larvae's suction organs work, we now envisage a whole host of exciting uses for engineered suction cups. There could be medical applications, for example allowing surgeons to move around delicate tissues, or industrial applications like berry picking machines, where suction cups could pick the fruit without crushing them."