The Cicadapocalypse – Part 3

The cicadas seem to be winding down here, so I'm posting about them one more time. In Part 2, I discussed how periodical cicadas know when 13 (or 17) years have passed. Now, let's consider how—after the allotted number of years—they know how to emerge within just a few days of all their fellow cicadas. Seriously... one day the forest is silent, the next day the cicadas are emerging and singing to the whole world (well, singing to attract a mate anyway). How do they all get the memo at the same time?

In my previous post, I stated that they emerge when the soil temperature reaches about 64ºF. True, but this can only be part of the story. Think about it... different areas of the soil reach 64º at significantly different times. Any area shaded by trees will be much slower to reach 64º. Deeper soil will also be much slower (cicada nymphs hang out underground for 13 or 17 years, but some of them are only a few inches deep, others are up to 18 inches deep). So, soil temperature alone does not explain how the cicadas emerge within a few days of each other.

Based on numerous observations of real cicadas, mathematicians and biologists at Cambridge created a complex mathematical model of a huge underground cicada brood. This allowed them to tweak different variables, one at a time, to try to discover what would allow the cicadas to emerge together, as real cicadas do.

After tweaking numerous variables, the scientists concluded the only thing that allowed the cicadas to emerge at the same time was if the insects were capable of communicating with each other underground. In the computer model, they gave the buried cicadas the ability to eavesdrop on the other buried cicadas near them. If the nearby cicadas (in slightly warmer soil) began making noise as they started climbing out of the soil, then the cicadas in slightly cooler soil were more likely to think, "Okay, I guess it's time to party!" (that's what I imagine cicadas are thinking after waiting 13 years underground for their time to emerge and finally mate).

Anyway, this computer model could only produce simultaneous emergences (like we see in the real world) if the scientists gave their simulated cicadas the ability to communicate underground.

Okay, well... we do not KNOW if real cicadas can communicate underground. Observing this will be difficult, but I'm sure biologists will come up with a way to do it. And I won't be surprised if the computer model turns out to be correct and underground cicadas really do have a way of talking to each other (maybe with clicking sounds?).

The mysteries of nature are endless, are they not?

Photo Credit:
13-year cicada - Stan C. Smith