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Published December 19, 2017 | public
Journal Article Open

Superhydrophobic diving flies (Ephydra hians) and the hypersaline waters of Mono Lake


The remarkable alkali fly, Ephydra hians, deliberately crawls into the alkaline waters of Mono Lake to feed and lay eggs. These diving flies are protected by an air bubble that forms around their superhydrophobic cuticle upon entering the lake. To study the physical mechanisms underlying this process we measured the work required for flies to enter and leave various aqueous solutions. Our measurements show that it is more difficult for the flies to escape from Mono Lake water than from fresh water, due to the high concentration of Na_2CO_3 which causes water to penetrate and thus wet their setose cuticle. Other less kosmotropic salts do not have this effect, suggesting that the phenomenon is governed by Hofmeister effects as well as specific interactions between ion pairs. These effects likely create a small negative charge at the air–water interface, generating an electric double layer that facilitates wetting. Compared with six other species of flies, alkali flies are better able to resist wetting in a 0.5 M Na_2CO_3 solution. This trait arises from a combination of factors including a denser layer of setae on their cuticle and the prevalence of smaller cuticular hydrocarbons compared with other species. Although superbly adapted to resisting wetting, alkali flies are vulnerable to getting stuck in natural and artificial oils, including dimethicone, a common ingredient in sunscreen and other cosmetics. Mono Lake's alkali flies are a compelling example of how the evolution of picoscale physical and chemical changes can allow an animal to occupy an entirely new ecological niche.

Additional Information

© 2017 National Academy of Sciences. Published under the PNAS license. Edited by Jerrold Meinwald, Cornell University, Ithaca, NY, and approved October 18, 2017 (received for review August 22, 2017). Published online before print November 20, 2017. We thank Jocelyn Millar, who generously performed the GC-MS analysis in this paper and provided valuable feedback on hydrocarbon chemistry; Rob Phillips, who also provided helpful comments on the manuscript; Dave Marquart, who helped procure necessary permits; Aisling Farrell, who helped collect Helaeomyia petrolei from the La Brea Tar Pits; and Victoria Orphan and Sean Mullin, who helped prepare SEM specimens. This work was supported by the National Geographic Society's Committee for Research and Exploration, Grant 9645-15. Author contributions: F.v.B. and M.H.D. designed research; F.v.B. and M.H.D. performed research; F.v.B. and M.H.D. contributed new reagents/analytic tools; F.v.B. analyzed data; and F.v.B. and M.H.D. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. Data deposition: All data in the manuscript have been uploaded to Github (https://github.com/florisvb/alkali_flies_of_mono_lake) and Open Science Framework (https://osf.io/43yhs/). This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1714874114/-/DCSupplemental.

Attached Files

Published - PNAS-2017-van_Breugel-13483-8.pdf

Supplemental Material - pnas.1714874114.sm01.mov

Supplemental Material - pnas.1714874114.sm02.mov

Supplemental Material - pnas.1714874114.sm03.mov

Supplemental Material - pnas.1714874114.sm04.mov

Supplemental Material - pnas.1714874114.sm05.mov

Supplemental Material - pnas.1714874114.sm06.mp4

Supplemental Material - pnas.1714874114.sm07.mp4

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Supplemental Material - pnas.1714874114.sm09.mp4

Supplemental Material - pnas.1714874114.sm10.m4v

Supplemental Material - pnas.1714874114.sm11.m4v

Supplemental Material - pnas.201714874SI.pdf


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August 21, 2023
August 21, 2023