I have a 1 1/2-inch long automatic bio-thermometer that sits in the Magnolia tree right outside my office. When it gets to be about 78 degrees or so a high pitched buzz emanates from the tree trunk. My “thermometer” is a woodland cicada. These amazing insects spend the first several years of their life totally in the dark, underground sucking on tree roots.

In the eastern US there are cicadas that spend up to 13 or, in the case of one species, even 17 years underground! The entire population emerges simultaneously, sheds their larvae skins, pumps blood into their new adult wings and then flies around looking for love. These massive insect invasions totally freak out suburbanites. But my sympathies lie with the critters, after all who built all those houses in the forest? For thousands of years the cicadas cycled out of the earth in tremendous numbers that overwhelm their predators (primarily birds). The males fly into trees and begin singing by vibrating two special membranes. Huge aggregations gather in deafening choruses. The females are silent but are attracted to the vibrating males. After the females lay eggs into twigs, all the adults die. The eggs hatch into larvae the size of a small ant, drop to the ground and dig down for the next 17 years!

So how do these animals keep track of time while underground? No sun, no moon, no day, no night, the temperatures are moderated. A scientist at UC Davis has recently discovered that cicadas can actually count blooming cycles. When a tree flowers there is a burst of sugars and proteins that flow throughout the plant and the cicadas feeding on the juices record this event. Amazing!

Our native woodland cicada however is non-periodical; that is every single summer there are adults present. Our species stay underground for one to three years and emerge when they are ready. The ones in the East are nothing but Tree-Sucking Clock-Watchers but the West Coast species march to their own individual molting drummer, none of this group emergence stuff. This is Michael Ellis with a Perspective.

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August 6, 2009