Signs of Fall 2: Cicadas in Colorado!

Megatibicen dealbatus (plains harvest fly). Photo by B. Bourassa, Wikimedia Commons

(Click on the following link to listen to an audio version of this blog …Colorado Cicadas!

(I wrote about Colorado cicadas last year (August 26, 2021). Since they have been singing so loudly this summer. it seems like a great topic to to reprise!)

Deborah and I were out walking the other morning. I was concentrating on keeping my body upright and my vision out ahead of my steps (I had grown used to watching my feet when I walked because of the gimpiness of my old knee. My new titanium knee didn’t need that kind of attention, so I was trying to see what’s ahead rather than what was underfoot!).  Anyway, thinking about my stride and my leg swing took most of my attention, but, suddenly, I heard a very familiar “sound of summer” that I used to follow closely back in Western Pennsylvania. It was the loud, throbbing, buzz of dog-day cicadas. They were announcing that summer was coming to end!

Mid-summer is the period of the year that the ancient Romans called the “dog days” in honor of the rising of the dog star, Sirius, with the morning sun. They thought that the heat and often unbearable humidity of the late summer and start of the fall were due to the combined powers of these two stars bearing down on the Earth. It was said to be a time of madness when wine soured and both man and beast hovered on the edges of despair and rage.

Tough time, indeed! The rage and despair common to both students and teachers right now, though, has more to do with the resumption of classes than with the celestial alignments.  One positive aspect of these hot days, for me anyway, is the emergence of these annual cicadas. Their buzzing songs high up in the trees gives a pace and a pulse to these long days.

The dog day cicadas have life cycles that range from two to five years in length. A given area, though, will have cohorts that reach their adult stages in the late summer of any given year. So, as we go into almost any August, we will be greeted by the nearly continuous singing of the annual cicadas.

Cicada “shell.” Photo by Pixabay

These cicadas begin their lives as eggs deposited in clusters under the bark of small tree branches and twigs. In six to seven weeks the eggs hatch into tiny nymphs which drop to the ground and burrow into the soil. They will live in the soil, feeding primarily on the sap from tree roots (especially oaks, ashes, and maples) for the next two or more years. They grow and undergo molts and metamorphic changes until at last they are at last ready to molt into their adult forms. In mid to late summer they crawl up out of the soil and climb back up the trunks of the same trees that housed their eggs and whose roots have nourished them through their development. On the trunks and branches of these trees the cicadas carry out their last molt and are transformed into adults. The dry exoskeletons of their pre-adult stages can often be found empty but still clinging to the rough surface of the tree bark!

Male cicadas climb further up the tree and begin to sing. They have thin, exoskeleton membranes (called “tymbals”) on the sides of their abdomens that they can pull inwardly and then release to make a loud “click.” The males’ bodies are also quite hollow and act as amplifying, resonance chambers for the generated sounds. The purpose of the song is, of course, to attract females for mating. The mated females will then lay their cluster of eggs under the bark of a twig or branch of the tree and start the life cycle all over again. Interestingly, the females have very solid, “meaty” bodies. They require more metabolic energy and more elaborate internal organs for the production of their eggs. One consequence of these morphological gender differences is that females are the preferred food for most cicada predators (including birds, squirrels, raccoons, and even people (many cultures include annual cicadas as a popular, seasonal food!).

The cicadas are abundant in certain yards up and down our block and, possibly, are confined to certain types of trees! I need to make more careful observations about the tree species/cicada relationship! The soils under these trees must be rich with developing cicada nymphs (which are feeding on secretions from the tree roots although, apparently, doing little damage to the trees). Each year a significant number of them mature and emerge. It is thought that the cicadas reduce their overall losses to predation by concentrating their adult emergences into a very narrow time window. Their numbers overwhelm potential predators and then they suddenly disappear. This transient existence also keeps predators from specializing on the cicada adults.

Other cicada species (called the “periodic cicadas”) have taken this idea of transient, predator satiation even further by extending their soil dwelling, nymphal stages out to thirteen or even seventeen years! These periodic “locusts” are so rarely abundant and when out are in such incredible numbers that predatory species are not only overwhelmed (and satiated) but also are stymied from evolving any specialized feeding strategies. Three years ago, I wrote about the periodic cicada emergence back in Pennsylvania (see Signs of Spring 7, April 18, 2019). Periodic cicadas, though, are not found in Colorado!

Megatibicien dorsalis (giant grassland cicada). Photo by V. Fazio. Flickr.

There are twenty-nine species of cicadas found in Colorado. Three of these are true dog-day cicadas (Megatibicien species). Megatibicien dealbaths is the “plains harvest-fly.” Its natural range is in the riparian woodlands of southeast Colorado, but it is now found in forested urban habitats all across the Front Range. It is the most common dog-day cicada in Colorado. A second, dog-day species is M. dorsatus (the giant grassland cicada). The giant grassland cicada is found in the shrubby grasslands of eastern Colorado and in the open grasslands that extend all the way west to the Front Range. A third, and much less common, dog-day cicada is the western bush cicada (M. tremulus) often associated with sagebrush.

Platypedia putnami (Putnam’s cicada). Photo by xpda. Wikimedia Commons.

Three other species of cicada are quite common in Colorado. Putnam’s cicada (Platypedia putnami) is naturally found in the Gambel oak and mountain mahogany thickets in the foothills of the Rockies. It has expanded its range, though, into the urban forests of many Front Range towns and cities. Some trees (like maple, crabapple and honeylocust) can sustain significant damage from this cicada’s ovipositor wounds in their bark. Interestingly, male Putnam’s cicadas do not have tymbal organs. The male Putnam’s cicadas make their mating calls by striking their two wings together to make a soft, rustling, clicking sound rather than the familiar cicada buzz.

Cacama valvata is the “cactus dodger” cicada. It is found in southern Colorado in association with

Cacama valvata (cactus doger cicada). Photo by P. Alexander. Wikimedia Commons

tree cholla cactuses and other shrubs. The call of the cactus dodger has been described as “ear splittingly loud!” It is by far the loudest cicada in Colorado. And, finally, Okanagana bella is the “mountain cicada.” It looks like a larger version of Putnam’s cicada and is found in high elevations especially in forests that are a mix of aspen trees and pines.

So the dog days are upon us! The cicadas are buzzing! I bet I can find some goldenrod (“summer’s end”) and some fall asters blooming out in a nearby field, too! Maybe I’ll walk over and check out the Fall plants! It is nice to be back on my feet again!