Earth Notes: Counting The Flies Of Grand Canyon

Dec 18, 2013

Grand Canyon river guides work long hours. In the last 2 years, some of them took on a seemingly unlikely new duty: collecting flies. By doing so, they've helped scientists learn more about the big canyon's aquatic food web.

Grand Canyon Flies
Credit Rose Houk/KNAU

Under the guidance of the U.S Geological Survey, guides set out traps on warm evenings to attract insects. The traps are simple: a Tupperware tray filled with ethanol, and a black light that serves as a lure. The guides then bottled up the bugs that ended up in the ethanol bath.

Aquatic ecologist Ted Kennedy of the Geological Survey tallied the bugs the guides collected during the last 2 years - thousands in all. Most were blackflies and midges. That's no surprise - these 2 species form much of the prey base for the river ecosystem. Both native fish and non native rainbow trout rely on them.

But, what Kennedy hopes to learn from the project is more about the timing of the insects' life cycles - when do they emerge into adulthood from the larval stage? That timing may be linked to daily and seasonal water releases from Glen Canyon Dam upstream. That's what Kennedy really wants to figure out.

More than 20 river guides have helped with the study so far. Because they're in the canyon every day from spring to fall, they've supplied a huge amount of data. Next year, other canyon visitors re invited to participate in this citizen science project, too. To learn how,