Monday, August 8, 2016

Colorado Cicadas by Rebecca Anderson

Dog Day Cicada (Tibicen dorsatus), photo courtesy CSU Extension

I've seen some news articles lately about 2016 being the year of the cicada in parts of the eastern United States.  Brood V of the 17-year cicada, made up of the species Magicicada cassini, M. septendecim and M. septendecula will emerge when the soil temperature reaches 64 degrees Fahrenheit and grace a six-state region with their song.  The emergence is expected to occur in May.  The last time this particular group of cicadas emerged was in 1999. 

Reading about this made me remember cicada emergence events from my childhood and I was thinking that I hadn't heard the magnificent insect symphony since moving to Colorado. This led to a little research where I learned that Colorado has a different cicada population compared to the eastern part of our nation. 

The periodical cicadas of the eastern United States have life cycles that require a 13 or 17 year  incubation before emergence. The mass emergence events result in noisy summers when the male cicadas "sing" to attract females. These large events led early European settlers to mistakenly refer to cicadas as locust because the noise seemed to be of a biblical scale. Unlike the swarming grasshoppers from the family Acrididae that are properly known as locust, cicadas are generally not destructive to plants. Some species will make small slits in the bark of twigs when laying eggs, but the population has to be numerous for this to be noticeable. A young tree may be more susceptible to damage, so in areas with large cicada populations it may be beneficial to cover the sapling with netting to exclude the cicada. The immature cicadas, called nymphs, develop in the soil, feeding on sap from roots of woody plants.  However, their feeding habits are minimal and do not result in damage to the plant.  When they leave the soil, the nymphs climb to a higher spot to molt. Their exoskeletons split down the back and a mature cicada emerges, leaving a dry cast of the nymph behind.  The fresh adult cicadas will rest on a branch until their wings dry, when they will fly away to find mates. 

The 26 species of Colorado cicadas, all of the order Hemiptera, have two to five year development cycles, and a few emerge every year. For this reason, we will hear some cicada "songs" each summer, but not the cacophony  experienced in the east. The male cicada produces his music with drum-like organs on the sides of his abdomen called tymbals. He contracts and releases muscles to make the tymbals vibrate. Then a large air sac in the abdomen acts like an echo chamber to greatly amplify the sound. Adult cicadas will live for four to six weeks, searching for the perfect mate.  Once the females have mated, they lay their eggs in bark crevices. When the eggs hatch, the nymphs fall to the ground and burrow into the soil to begin their two to five year maturation process. 

Cicada Killer Wasp (Specious speciosus), photo courtesy CSU Extension
Although cicadas are some of the largest insects encountered during the summer, they are not aggressive toward humans. They do not bite or sting. When they are startled, they will make a buzzing noise that seems hostile, but it is only a scare tactic. In fact, cicadas are a food source for several other insects and birds. The most visible is the cicada killer wasp (Sphecious speciosus), that looks like a giant yellow jacket. However this giant solitary wasp is not interested in stinging humans or animals. The adult wasp feeds on nectar from flowers and uses its stinger to paralyze cicadas to transport them back to the wasp’s underground nest to feed her young. 

To learn more about Colorado cicadas, check out CSU Extension's Fact Sheet on Cicadas. The website has information about emergence events of the periodical cicadas in the eastern United States.