Sea butterflies are snails that have inverted themselves. Instead of using their flesh (via a foot) to crawl on the sea floor, they turned upside down and make their protruding bodies into “wings.” When scientists studied this unusual motion, they found the sea butterflies move exactly like fruit flies and other small insects.

In a new paper in the Journal of Experimental Biology, researchers at the Georgia Institute of Technology described their investigation into how the sea butterfly stays afloat. The sea butterflies (and the insects) fly using what the researchers describe as “the well-known Weis-Fogh ‘clap-and-fling’ mechanism.” It’s essentially a figure eight pattern.

First the snail claps its wings together at the top of its stroke. Instead of keeping the wings rigid and pulling them down and apart (which would move the water under the wings and no more), they peel the wings apart. Instead of pushing water with their wings, they suck water down between their wings. This displacement of water causes vortices of low-pressure water to form right at the wing tips, and it’s the vortices that pull the snail up.

Insects and sea snails split off from each other pretty early, in terms of evolution. Their physiology, their environment, and physics, caused them to evolve the same strategy for getting around.

“No one has actually been able to measure the flow around an insect doing this while it is flying, and so that was kind of the holy grail of this area of research,’ co-author David Murphy said in a statement. “It really surprised me that sea butterflies turned out to be honorary insects.”

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[Journal of Experimental Biology, Bizarre Snail That Swims Like a Flying Insect]

Top Image: PLoS ONE Video: The Company of Biologists