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Do Not Shave a Fruit Fly’s Eyes

(Clip of a fruit fly cleaning itself slowed by 33x. Credit: Guillermo Amador at Georgia Institute of Technology.)

From a distance, insects can appear smooth and sleek, but get close enough and hundreds of tiny bristles called setae come into focus. Suddenly what once seemed smooth now resembles a porcupine terror.

For certain insect species, setae cover many parts of the body including the legs and eyes. The tiny hairs contain nerves that signal to the insect when dust, pollen, mold or other particles are on its body. Moreover, insects use setae as combs to clean themselves by rubbing the bristles against each other, which flicks debris away.

These are just two examples of the many applications setae serve insects and there are still more to be discovered. A team of scientists at Georgia Institute of Technology recently found another application of setae on the eyes of fruit flies.

They designed a mock model of a fruit fly eye with 282 evenly spaced fibers and a film of water at the base, representing the surface of the eye. By placing the model in a wind tunnel and measuring the evaporation rate of the water, the team could measure how much airflow reached the mock eye’s surface and how much the fibers diverted.

The team found that the fibers could divert up to 90 percent of airflow away from the surface of the eye. This helps keep a fruit fly's eyes clean of debris as it flies. So, part of the reason a fruit fly can see you coming with your swatter is because its hairy eyes protect the eyes' surface from debris clutter.

“These setae are very multifunctional,” said Georgia Tech PhD student Guillermo Amador who was part of the study. “And it’s such a simple thing. It’s just a bristle. It’s interesting how insects have been able to integrate many functions into this bristle.”

Top Row: Fruit fly and a microscopic image of its eye that clearly shows the setae. Bottom Row: Honey Bee and microscopic image of its eye, which also has setae. Credit: Guillermo Amador 

To clean off the small amount of debris that the setae do not divert, a fruit fly will rub its hairy legs against its equally hairy eye. This motion can catapult microscopic particles off and away from the eye’s surface at accelerations over 100 g, the team calculated with high-speed videography, like the clip shown above.

In addition to insect eyes, there are many microelectronic devices that could benefit from setae-like fibers. For example, charge-coupled devices (CCDs) in Digital SLR cameras need to stay debris particle-free. If dust particles land on a CCD, they will obstruct light particles from reaching the device thus reducing image quality.

“The dual abilities of setae to divert airflow and catapult particles may motivate bio-inspired designs for dust-controlling lenses, sensors, and solar panels,” the team stated in an abstract they submitted for the 66th Annual Meeting of the APS Division of Fluid Dynamics. They will present their findings in more detail at the event held in Pittsburgh, PA from November 24 to 26.

Using theoretical models based from their experimental data, the team hopes to determine the optimal bristle array and length that maximizes airflow diversion capability. They have already partnered with laboratories at Georgia Tech to apply their results toward building an efficient method for cleaning microelectromechanical systems (MEMS) cantilevers, a common type of MEMS that have applications in biosensor medical diagnostics.


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