Though they make a lot of noise in adulthood, mountain cicadas have a quiet period of growth. Photo by Jeff Mitton.
By Jeff Mitton
The western portion of Hall Ranch seems to have an excellent recipe for quiet serenity: an excellent view of the continental divide, meadows filled with flowers, and stands of ponderosa pines. But on this day, the hush of breeze in the meadow was drowned out by a shrill note that emanated from all points of the compass. Mountain cicadas were calling.
Twenty-seven species of cicada are native to Colorado, but only one is common in the mountains. The mountain cicada, Okanagana bella, is found from the lower edge of the ponderosa forest to about 10,000 feet. It is found in all of the western states and British Columbia and Alberta. In the last two weeks, I found mountain cicadas at Heil Ranch and on Flagstaff Mountain.
Another cicada is in ponderosa forests right now. Wing bangers, also Putnam's cicada, Platypedia putnami, are on ponderosa pines at Hall Ranch and in Fourmile Canyon. Mountain cicadas and wing bangers are both large cicadas, one to more than two inches long, and both are black with red piping, so how does one distinguish them? The mountain cicada has more red piping than wing bangers, particularly on the abdomen, but these species are most easily distinguished by their calls.
Mountain cicadas, like most species of cicadas, make sounds with a paired set of organs called tymbals at the base of the abdomen. Abdominal muscles contract the tymbals up to 50 times per second, flexing dried tymbal membranes to generate sound.
The shrill call of the male mountain cicada is a clicking buzz that lasts from 10 seconds to two minutes. Wing bangers lack functional tymbals, but make a clicking sound by banging their wings against their perch or against their abdomens. Only male mountain cicadas call, while both male and female wing bangers click.
While it is difficult to escape their noise, you must search to see cicadas. I have had success scanning small ponderosa pines at the periphery of stands. Cicadas are sometimes sedentary, sometimes moving slowly along smaller branches, but not at the branch tips or in the needles.
Some are wary; others are not. A calling mountain cicada, at eye level, was unperturbed by my approach to within three feet and continued its intermittent declaration of his masculinity.
Cicadas have bizarre life cycles. Females generally lay eggs in slits in tree branches or on plant stems. A tiny cream-colored egg hatches in 70 to 120 days, releasing a pronymph that drops to the ground and burrows more than a foot into the soil, seeking tree roots from which it will feed.
Cicadas feed on roots for years, but for most of the western cicadas, the number of years spent feeding underground is unknown. The periodic cicadas, famous for eruptions of dense populations in eastern deciduous forests every 13 or 17 years, do not occur here. Both mountain cicadas and wing bangers appear every year, but we do not know how many years the nymphs feed underground.
After a nymph digs up to the surface with its large front legs, it attaches to a piece of vegetation, the nymphal skin splits, and the adult wriggles out, leaving behind the cast nymphal skin, an exuvia or exuvium. Exuviae litter mountain meadows in early summer, providing an eerie census of the emerged.
When it wriggles free of the exuvia, the emerging adult is pink and green with soft, stubby wings. The wings expand to full length within and hour and the soft pink and green exoskeleton or skin dries and hardens, turning to red and black. The adult can fly a few hours after emerging from the ground.
After years of subterranean silence, the males are ready to make a racket and females are ready to choose among stridently sonorous males.
Jeff Mitton (mitton@colorado.edu) is a professor in the Department of Ecology and Evolutionary Biology at the University of Colorado.
July 2011