Last call for cicadas?

    Alas, we near the end of our discussion about cicadas just as the insects themselves are winding down their mating season. Readers wrote in with questions about how they make noise, whether they’re all periodic, how to track their cycles, and where to find further resources. We have answers.

    Alas, we near the end of our discussion about cicadas just as the insects themselves are winding down their mating season.

    Within the next few weeks the sound of the males’ nuptial songs will subside. The females will cut slits into twigs, depositing hundreds of eggs each into the tree canopy. Sometime this fall the eggs will hatch, and the nymphs will rain down inconspicuously to the ground where they will burrow for anywhere between two and seventeen years.

    Several readers were kind enough to post comments about cicadas, so I’ll finish my cicada miniseries by responding to them. Remember: I’m not an entomologist. I just sometimes play one on this blog.

    Q: How do they make the noise?

    A: A lot of loud insects make noise by rubbing one body part against another, like a musician playing the violin. Not the cicada. Instead, picture it as an accordion player. The male has a mostly hollow abdomen, and part of its exoskeleton has a membrane made up of ribbed muscles called tymbals. When the tymbals contract, the buckling action causes a clicking sound. As they relax, they produce another click. By doing this rapidly they can create the familiar buzzing or whirring sound we’re hearing.

    The buzz of cicadas often seem to start with one song, then grow to a crescendo before quieting down again after a few minutes. This is probably because since the songs are mating calls, each male is in competition to draw females towards itself and away from other males. To anthropomorphize here, imagine the male cicadas screaming “Look at me!” “No, look at me!” “Ignore them- look over here!” until they get tired and stop until the next one starts up again.

    Q: Are all cicadas periodic?

    A: Sort of. It seems that all cicadas live underground for multiple years, usually between two and eight. But these cicadas aren’t synchronized, so every year there will be some that emerge. The true periodic cicadas are completely synchronized. Some broods emerge every thirteen years and others emerge every seventeen years. These seem like random amounts of time, but because both of these numbers are prime it ensures that the two types of periodic cicadas will only emerge at the same time once every 221 years. This is probably good for two reasons. It minimizes the opportunities of the two types to interbreed (which in theory could mess up their synchronicity.) It also prevents the total habitat destruction that could take place when so many cicadas emerge at once to suck the sap out of young trees. Because when the periodic cicadas emerge, they do so in great numbers, like thirteen or seventeen times what you would expect in a regular year.

    A lot of studies have been done to try to trick periodic cicadas to emerge on off years, for example fertilizing the trees that the nymphs feed on. It doesn’t work. They still stay in the ground for the preordained amount of time, and emerge en masse with the rest of their brood (although in the study the ones that had been under fertilized trees emerged as larger insects.)

    Q: Is there some way to track their cycles?

    A: There is a project that’s tracking the 2011 emergence of the periodic cicada, named Brood XIX, including its presence in Southeastern Pennsylvania. Check it out here.

    Q: Are there any other cicada resources?

    If you want to learn more about periodic cicadas, this document on their ecology, behavior, and evolution is pretty interesting and not overly technical.

    But the best, most inspiring website I found related to cicadas is Cicada Mania, sponsored by the Entomological Society of America. Here you can order a t-shirt or trucker hat commemorating the emergence of Brood XIX (I chose the shirt.) There are also instructions for simple cicada experiments and lots of photos and videos. They have even created a tool that will help you figure out if a periodic cicada emergence is likely to interfere with your outdoor wedding, which is the sweetest thing I’ve ever heard of.

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