It was early afternoon in mid-July 2019 and my first time setting foot on Antelope Island. As a newcomer to Utah, I was itching to explore the local sights and had come to learn about the impressive annual shorebird migration from my friend, a bird enthusiast and fellow graduate student.
Brimming with excitement, and a little put off by the smell of Great Salt Lake mud wafting through the open windows, we parked the car in the Antelope Island Marina parking lot and jumped out onto the shore of the famed isle. Thousands of birds dotted the water around the harbor, and the ubiquitous Antelope Island spiders blanketed the bushes with innumerable webs. But it wasn’t the birds stretching as far as the eye could see out on the waters of Great Salt Lake, or the impressive number of spiders skittering past our car tires that left a lasting impression on me.
As we stepped out onto the beach to get a closer look at the birds bobbing on the salt water and to set up the birder’s favorite tool, a spotting scope, the dark grey sand under our feet sprang to life with a gentle buzz. The sand, or what I thought was sand, was actually a shoal of brine flies, easily numbering in the millions. Surprised by our discovery and shorebirds completely forgotten for the moment, we walked slowly along the shore, and with each step, a cloud of flies jumped up to avoid our footfalls, gently settling back down behind us as we walked on.
Brine flies, which are small flies in the genus Ephydra, are a common occurrence around the lake. These gentle flies do not bite, and as adults, they don’t even have mouth parts to feed with. Much like mayflies, they only live a few days as adults, with the goal of reproducing and laying their eggs back in the waters of Great Salt Lake to start a new generation of flies.
Similar to an aquatic caterpillar, their larval stage lives in the briny waters of Great Salt Lake, feeding mostly on algae and other organic matter. At their peak population around Great Salt Lake each year, brine flies are estimated to number in the billions, and the skins they shed as they emerge from the water as adults pile up on the shore in incomprehensible numbers.
As such an abundant insect around the lake, they provide critical food for all manner of creatures. Our momentarily forgotten shorebirds are avid predators of brine flies, and, hungry from migration, these birds snap up brine flies by the thousands. Phalaropes, stilts and sandpipers are just a few of the bird species that feast on brine flies. Gulls love to feast on brine flies, and in silly gull fashion, go about chasing them up and down the beaches with open beaks and loud wails. Remarkably, for eared grebes, brine flies can make up 40 percent of their diet, while the remainder usually consists of another Great Salt Lake denizen, the brine shrimp.
Birds aren’t the only ones that rely on brine flies for food. Spiders, like the ones keeping us company in the Antelope Island bushes, as well as beetles and other invertebrates, feast on brine flies too. In fact, as scientists say, brine flies are an important part of our Great Salt Lake ecosystem. Walking slowly along the shore with my eyes pointed down toward the great clouds of brine flies at my feet, it was easy to see how their sheer numbers could feed an army of critters.
As someone who spends most of my time thinking about birds that eat fish and how to study them, I’m not one to trouble myself with thoughts about insects often, but thinking back on that remarkable July afternoon and the struggling health of our Great Salt Lake, I can’t help worry a little for the future of our gentle brine flies.
I’m Aimee Van Tatenhove, and I’m wild about Utah.
https://wildlife.utah.gov/gslep/wildlife/brine-flies.html
https://www.allaboutbirds.org/guide/Eared_Grebe/lifehistory
https://birdsoftheworld.org/bow/species/eargre/cur/foodhabits
