#23: Cicadas

From <https://en.wikipedia.org/wiki/Cicada> © Bruce Marlin

Litinsects #23: Cicadas

When I was a kid, I once found this crazy looking thing attached to a tree in my yard and I kept it because I was so fascinated. It wasn’t until a decade later that I realized what that thing had actually been... the exoskeleton of a cicada.

Cicadas might be a pain because of the deafening noise they can make but they are really interesting and cool-looking insects.

• Cicada calls are produced by TYMBALS, which are complex structures on the abdomen with membranes and thickened ribs. The membranes vibrate extremely quickly and the cicada’s body acts as a resonance chamber to amplify calls

• The calls are so LOUD that males disable their own tympana (remember, insect ears?) so that they don’t damage them. At close enough range, they can actually damage human hearing!

• ANNUAL CICADAS appear every year. Most species spend years underground during their nymphal stages but there is no sort of coordinated emergence

• PERIODIC CICADAS, on the other hand, time their life cycle so that all members of a population reach adulthood at the same time. Their synchronized emergence occurs only once every 13 or 17 YEARS! This is a great strategy because (1) any predators feeding on them will become satiated before being able to make a big impact on the population size and (2) no predators can evolve to depend on cicadas as a food source because they would starve until the next emergence

Fun fact: The cycles of period cicadas are PRIME NUMBERS and there’s a pretty cool reason for that. Many predators have population cycles of a few years (meaning their population size peaks in some years but is lower in others). Low and even numbered cicada cycles would synch up with predator cycles much more often, resulting in more cicadas being eaten at every emergence. By timing their emergence as a prime number, the chances that it coincides with a predator’s peak population size OR with that of another species of periodic cicada are massively reduced. Nature is pretty smart that way!