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Brine Flies

August 12, 2010

The Great Salt Lake is slightly larger than the state of Rhode Island but much smaller than Lake Ontario, the smallest of the Great Lakes. The salinity of the Great Salt Lake varies in different parts of the lake and from one year to the next, but on average it is twice as salty as the oceans and may be more than ten times saltier than sea water. Very few organisms can survive the high salt concentrations. A few forms of algae flourish in the inhospitable waters. Two native animals also are found, brine shrimp and brine flies.

During the summer brine flies proliferate. Some years their numbers are so epic, so staggeringly large, as to approach a biblical scale. If Moses and Pharaoh had staged their encounter in northern Utah, rather than Egypt, there would undoubtedly have been a plague of brine flies mentioned in the Old Testament. The flies are small and do not bite. But they manage to find their way onto every stationary surface and, unless precautions are taken, into every nook and cranny one may imagine, including eyes, ears, nostrils, open mouths, and a few others anatomical features that will pass unmentioned.

A few years ago, in the name of science, I conducted an informal experiment. On a warm summer morning I made the seven mile drive from the eastern mainland to Antelope Island, one of the lake’s larger islands, across a causeway constructed in the 1960s to connect the two. I made the trip slowly, with all of my windows down, and then I reversed my course and returned to the mainland, slowly again. I birded as I drove but also, I was curious as to how many brine flies might accumulate inside the vehicle if I did not drive so fast as to blow them out. By the time I returned to the mainland there were an average of 1-2 brine flies on every square inch of the vehicle’s interior, myself included. I’m not sure how many thousands of the insects I collected during this short drive, but even after repeated cleanings, then and over the intervening years, I continue to find dead flies from this one morning’s drive. My only consolation is that I had the foresight to conduct this experiment in my wife’s car rather than my own.

Millions of birds take advantage of this plentiful and abundant food source as they migrate across Utah to their winter homes. Waterfowl, waders, and shorebirds easily pluck brine flies from the lake’s surface and mud flats. Dead insects accumulate in drifts at the water’s edge, like banks of dirty snow, and a variety of land birds forage through these all-you-can eat buffets. A few species, such as California gulls, have an interesting approach. They simply open their bills and run through a swarm of airborne flies, until they tire or the flock of flies thins. Then the gulls turn and run back in the opposite direction, bills open, again gorging on the run.

Bird numbers along the shores of the Great Salt Lake have been escalating over the last few weeks as Fall migration begins. As one drives the causeway one never knows what one might see, as the road serves as an artificial collecting point for the flies and therefore also for birds. Birders also accumulate in large numbers along the causeway, scanning the flocks with binoculars and spotting scopes. You can easily recognize those who have birded the causeway before. Their windows are shut and their mouths remain closed.

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