We seem to have a new abundant crop of cicadas this past week as seen in the pictures above. I counted a dozen on the tire of one of our vehicles. It is fascinating to understand how they all know to come out of the ground at the same time.
Here is what I found out:
“The year of cicada emergence is cued by what I and others believe to be an internal molecular clock,” she said. “The clock is most likely calibrated by environmental cues that signify the passage of a year, such as the trees leafing out, changing the composition of the xylem fluid on which they feed. The molecular clock keeps track of the passage of years. The accumulation of 13 or 17 years triggers the emergence of fifth instar nymphs. The day of emergence is triggered by accumulated ground temperature. This was demonstrated by James Heath in a study published in 1968.”
My colleagues and I hypothesize a molecular clock in periodic cicadas that somehow keeps track of the years,” he said. “That is what we’re looking for now. We suspect it is tied to yearly cycles of the trees they are feeding upon.”
In 2007 in Cincinnati, it was warm in January but there was a hard freeze in February, and then a normal spring, which caused maple trees to produce two leaf sets that year. Hundreds of cicadas feeding on those trees emerged a year early, after the trees produced 17 leaf sets in 16 years.
During years when they are set to emerge, the time of year is determined by soil temperature.
“Emergence is temperature driven,” said Dr. Kritsky. “During the last emergence in our area, I planted temperature probes in the ground all over campus to track the emergence. The cicadas emerged over a period of two weeks after the soil temperature reached 65 °F (18 °C).”
P.S.
Roasted cicadas anyone? They are gluten free!
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