Aquatic robots could soon float like tiny insects on the surface of the water, after researchers in China discovered how the tiny animals stay afloat.

Mosquitoes, water striders and some other insects are able to float on the surface of water partly due to the fact that their legs repel water.

China University of Petroleum (Huadong) researchers, together with colleagues from the Liaoning University of Technology, examined how the tiny creatures stay on the surface of the water.

Mosquito legs consist of three main segments. The femur is attached to the abdomen on one side and connected to the tibia at the other end. The tibia then attaches to a tarsus. Each of these parts is coated in scales which repel water, assisting the insect in floating.

The tarsus was largely ignored in most previous studies of how the insects floats. This new research measured the role of the tarsus through the application of a small needle, indenter column and microsensor to the segment. This allowed investigators to modify the angle and force between the leg and surface of the water, while studying the results with a digital camera and microscope.

The insects are able to float due entirely to the hydrophobic nature of the tarsus, as it lays horizontally on the surface of the water, researchers discovered. The flexibility of the tarsus is able to control how much force is applied to the surface. This system can support up to 20 times the weight of the insect, investigators discovered.

"The current analyses deepen our understanding of the mechanisms of water-walking of these aquatic insects," Jianlin Liu from the China University of Petroleum said.

Mosquitoes float on water to lay eggs just under the surface. When they hatch, the pupa mature into adult insects, and travel to the surface of the water, where they take to the air. When the insects want to take off, they tilt the tarsus, which reduces the adhesion of the insects to the water.

Examination of the processes some insects use to stay afloat could assist researchers in developing ultra-small boats, submarines and other biomimetic structures. Machines and materials inspired by nature are in widespread use around the world in other applications, including Velcro, which was based on burrs, commonly found on socks after a walk through the woods.

Future research will examine how the tarsus is able to produce such a great buoyant force for a given length. The tiny structures will be examined in detail, and compared to dynamic behavior of wet adhesive forces to determine how the tarsus is able to completely support the weight of the insect.  

Analysis of the role of the tarsus in mosquitoes was published in the journal AIP Advances.

Photo: Ton Rulkens | Flickr

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