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Mountain cicadas, Okanagana bella, are also found locally, and it is the only cicada common in the mountains

"What is that sound?" people asked. It was emanating from shrubbery and trees in town and from aspen and ponderosa pine along trails in Boulder's greenbelt. Many people suspected that it was cicadas, but the sounds were not right. These sounds were a soft and slow tapping, like the sound of typing on a manual typewriter, instead of the raucous, protracted blaring usually associated with cicadas. Cicadas were indeed the source of the noise, but not the cicadas that most people are familiar with or have heard about.

The word "cicada" usually brings to mind the seven species of periodic cicadas native to the east coast and the eastern edge of the Great Plains. Their life cycles or generations are very long, either 13 or 17 years spent sucking sap from the roots of deciduous trees, then a climactic emergence that resembles an eruption. Densities of 1.5 million per acre have been reported for 17-year cicadas. Once above ground, males gather in a tree to form choruses to call and females come to the chorus tree to mate. The periodic cicadas can be very loud--sounds have been measured in excess of 100 decibels, which is the pain threshold for human ears, and some choruses have been heard from a distance of 1.5 miles. But none of the periodic cicadas are found west of the Great Plains.

Twenty-nine species of cicadas occur in Colorado, and their life cycles, which are also their generations, range from two to five years. Only two species are common locally, and adults of both species appear each spring, so they are referred to as annual cicadas.

Putnam's cicada, Platypedia putnami, is the most common in town and in lower foothills sites such as Gregory Canyon and Flagstaff Mountain. Its soft, tapping song is typical for species in the genus Platypedia, which are sometimes referred to as wing banger cicadas. They produce their call by clapping their wings against their abdomens or the branch that they are perched on. Males call or sing to attract females and females signal acceptance by returning his call with their wings.

A Putnam's cicada calls from a cottonwood twig cut numerous times to insert eggs below the bark. Photo by Jeff Mitton.

Mountain cicadas, Okanagana bella, are also found locally, and it is the only cicada common in the mountains, from the lower edge of the ponderosa pine forest to 10,000 feet. Its song is a shrill buzz that lasts from ten seconds to two minutes. These calls are loud if one is within a few feet of a calling male, but not nearly as loud as the periodic cicadas. The shrill calls are produced by tymbals, a pair of organs in the abdomen, each composed of a ribbed membrane that, when deformed 50 times per second by abdominal muscles, makes numerous clicks, the sound we hear as a shrill buzz. 

Mountain and Putnam's cicadas are most easily distinguished by their calls, but other characters will distinguish them. Mountain cicadas are larger, and their head and thorax are proportionately larger, bulging above the level of the abdomen. Both species have reddish-orange piping, but the mountain cicadas have much more conspicuous and brighter piping circling the abdomen.

One area on Flagstaff has so many cicadas that I found two or three on the same branch, which made me wonder if cicadas have chemical defenses protecting them from predators. The answer is that everything considers them edible--their list of predators is very long and it includes humans. Recipes for preparing cicadas are readily available online: spicy popcorn cicadas, tempura cicada, cicada chips, soft shelled cicadas, cicada cocktail and many more. Birds, rodents, snakes and lizards all eat cicadas. While all of these predators will take cicadas when they are conveniently available, a group of wasps relies on and specializes on cicadas. 

Two species of cicada killer wasps occur in Colorado, the eastern cicada killer, Sphecius speciosus, and the western cicada killer, S. grandis. They are large, up to two inches long, and strikingly colored, with a background of shiny black, a reddish-brown band on the thorax, ornate yellow lines on the abdomen and amber wings. Females are much larger than males and females have stingers, males do not. Females search for a cicada, paralyze it with a sting, grasp it upside down beneath her body and fly back to her burrow. Each egg chamber in her nest will have one egg with 1 to 3 cicadas, waiting motionless, to provide nourishment for the growth and development of the larva.

It would be engaging to watch cicada killer wasps hunting and provisioning their nests. The cicada killers have not been seen in Boulder or in our greenbelt, but they are along the South Platte River, just 20 miles away. With climate warming, they will be here soon.

A dense population of Putnam's cicadas. Photo by Jeff Mitton.