Scales Allow Floating

a mosquito sits on a green leaf with a blurry green background

Biological Strategy

Mosquitoes

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Move in/on Liquids

Water is not only the most abundant liquid on earth, but it’s vital to life–so it’s no surprise that the majority of life has evolved to thrive on and under its surface. Moving efficiently in and on this dense and dynamic substance presents unique challenges and opportunities for living systems. As a result, they have evolved countless solutions to optimize drag, utilize surface tension, fine tune buoyancy, and take advantage of various types of currents and fluid dynamics. For example, sharks can slide through water by reducing drag due to their streamlined shape and specially shaped features on their skin.

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Modify Buoyancy

Buoyancy is an upward force exerted by air or liquid on a solid object that works against the object’s weight. A hawk glides through air and a duck floats on water due to buoyancy. Some living systems (such as fish eggs) can remain sedentary and therefore maintain the same buoyancy at all times. But most must adjust their buoyancy because they can’t survive long unless they change position. These living systems require strategies to not only be buoyant, but also adjust buoyancy level. They often modify buoyancy by adding or decreasing lift, or by changing their weight. For example, birds like condors that soar for a long time shift the directional orientation of their wingtip feathers to manage buoyancy. Fish alter the amount of air in their swim bladders to increase or decrease their weight, thus altering their buoyancy.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Legs of mosquitoes allow it to float due to scales that structurally maximize trapping of air.

“We found that the mosquito’s legs are covered by numerous scales consisting of the uniform microscale longitudinal ridges (nanoscale thickness and microscale spacing between) and nanoscale cross ribs (nanoscale thickness and spacing between). Such special delicate microstructure and/or nanostructure on the leg surface give a water contact angle of ~153° and give a surprising high water-supporting ability. It was found that the water-supporting force of a single leg of the mosquito is about 23 times the body weight of the mosquito, compared with a water strider’s leg giving a water-supporting force of about 15 times the body weight of the insect.” (Wu et al. 2007:1)

micrograph showing detail of mosquito leg with many overlapping scales each with tiny ribs

Image: Wu et al. / Physical Review E / CC BY - Creative Commons Attribution alone

The hierarchical microstructures and nanostructures of the scales on a mosquito’s leg. Above: The numerous scales on the leg surface oriented along the leg; Below: the elaborate arrangement of the longitudinal ridges and the cross ribs of each scale.

Last Updated September 14, 2016

References

Journal article

Micronanostructures of the scales on a mosquito’s legs and their role in weight support

Physical Review E | 06/07/2007 | C. W. Wu, X. Q. Kong, Diane Wu

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