Shield and Spoilers Decrease Lift in Water

Biological Strategy

Mayfly

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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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Manage Turbulence

A turbulent force occurs when air or water creates a chaotic or irregular motion. The source can be such things as wind, waves, and eddies caused by obstructions to air or water flow (such as that created by a rock in a stream). Because the force is irregular, it acts in unpredictable ways on multiple parts of a living system at any given time, decreasing the living system’s efficiency. Strategies used to manage turbulence include dampening the amount of turbulence, having flexibility to handle sudden changes, and making quick adjustments. An example is the mucus on aquatic organisms, such as barracuda sharks, that can reduce turbulent friction of seawater by 66%. In doing so, it decreases drag and increases the sharks’ swimming efficiency.

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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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Body of Ecdyonurus (mayfly) larvae decreases lift in flowing water by having a lowered head shield position and using its lower leg segments (femora) as spoilers.

“Not only does flow separate above a flattened animal, but it is also much more complex than was first thought. Flow separation reduces lift, but at a cost of increased drag which, however, is a price that may well be worth paying to stay attached. For the heptageniid larvae, certain features of its body design may in fact lead to negative lift in flowing water. This is accomplished by lowering its head shield and by using its femora as spoilers (Weissenberger et at. 1991) (Fig. 5.3).” (Giller and Malmqvist 1998:112)

Last Updated August 18, 2016

References

Book

The Biology of Streams and Rivers (Biology of Habitats Series)

Oxford University Press, USA | 18/02/1999 | Paul S. Giller

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