City Creek Nature Notes – Salt Lake City

May 18, 2017

May 16th

Filed under: Ants, Millipede, Pill bug, Snag tree, Stink Bug, Stream — canopus56 @ 9:30 pm

Insect Home

4:30 p.m. It is overcast again and temperatures have dropped into the high fifties due to a rare front moving in from the northwest. About twenty song birds continue to clump at the Guardhouse Gate, near picnic site 4, and in Pleasant Valley. Although the flood retention pond is down by two feet, the stream continues to flow near its maximum. At picnic site 8, I stop to take a comparative photograph of the stream. In the winter (December 20th), the surface of the stream froze to a milky white stone. Now at this same location, it is a rushing, undulating mass of force and chaos. But in its chaotic motion, there is regularity. The stream rises and falls in standing waves about eight feet apart. Where the stream is confined and flows greatest, these waves begin to break back upstream. More velocity results in a tumbling jumble of splashing white water.

Walking back to the road from the stream side, I notice a decayed, fallen log about eight inches in diameter. It’s pitted surface, marked by boring insects, is a kaleidoscope of colors: tan, dark brown, dark red, Frank Lloyd Wright’s favored Cherokee red-orange, blacks, greys and tints of blue-lichens. I kick the log to break it apart, and as it splits, insects scurry and run for cover deeper within its rotting depths. The log is inhabited by three insects that I regularly pass on the road. First are the Carpenter ants. Second are common pill bugs. Finally, there is a small, brown 1 millimeter diameter unidentified millipede. Underneath the log, there is two or three inches of fine sawdust. Further down canyon, I pull apart a larger 14 inch diameter rotted log. Inside a stink bug is startled and runs into a crevice. The few of these insects that I see on the road are migrants from parent colonies in fallen logs that line the road.

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In an article of first impression, Comiti and Lenzi of the University of Padova studied the physics of standing waves in mountain streams (Comiti and Lenzi 2016). Standing waves have long been known to form in larger rivers, such as the ten foot high waves of the “Silver Dragon” in Qiantang River, China, and those waves have been well studied. Standing waves do not occur because the stream bed is carved into similar undulations, and the surface water simply rises and falls in response to that lower, hidden surface. The dunes beneath the stream’s surface are an effect, and not the cause of the bed’s undulations. Standing waves form when part of the surface of the river moving upstream and not downstream. The interference of the two motions generates an oscillation that takes of the form of a stationary wave. Comiti and Lenzi built artificial mountain streams and studied how the standing waves scour the stream bed into slowly upstream moving anti-dunes.

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On May 16th, 2003, the Deseret News features photograph of joggers in City Creek Canyon. On May 16th, 1936, City Commissioner George D. Kesyer warned residents to keep their children away from City Creek Canyon stream during spring run-off (Salt Lake Telegram).


September 20, 2016

July 31st

Filed under: Butterfly, Insects, Pill bug — canopus56 @ 10:38 pm

Pill Bug Explosion

5 p.m. Midsummer is the most productive time for insects in the canyon. Many insects pursue an R reproductive strategy. They produce as many offspring as possible in bursts of mating in the hope that a small number of offspring might survive. In the canyon, an example is the butterfly explosion that occurs in April of each year. I have seen densities of upwards of 1000 butterflies per mile in the canyon during their brief two or three day explosion. Today, it is the turn of the lowly common pill bug (Armadillidium vulgare). But this bug is not an insect; it is a land dwelling crustacean. As I jog up the road, typically I am looking down at my feet. I count 3 pill bugs for each 25 steps in a 5-foot wide swath of road. Each step is about 2 feet long and jogging up to milepost 2 is about 10000 feet. Extrapolating this density to a 150 foot wide strip on either side of the road gives an estimate of 36,000 pill bugs. Pill bugs eat decomposing vegetation. This shows how even the smallest innocuous animal affects the ecology of the canyon. A few days later there are no pill bugs on the road.

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