The Brood

As I sit, I lis­ten to the buzz of a mil­lion rav­en­ous, lust­ful insects. My usu­ally peace­ful neigh­bor­hood has been invaded by a swarm of black, red, and orange crea­tures who have emerged from the earth like zom­bies and have pro­ceeded to lay claim to all before them. I speak, of course, of the periodical cicada.

This is Brood II, actu­ally and it’s kind of a sur­real expe­ri­ence. This is not the first time I’ve seem the cicada’s emerge in this area. The last time it hap­pened, how­ev­er, I was in high­school. (That was a dif­fer­ent brood.) Sim­ply sit­ting on my porch, I can’t actu­ally see any cicadas aside from the occa­sional orange speck in the dis­tance. The rea­son that the apart­ment com­plex I live in was built since the last time this brood emerged, sev­en­teen years ago. I can still hear them however; their mat­ing buzzes make for an omi­nous roar.

Across the park­ing lot, in the direc­tion I’m fac­ing is an old park ded­i­cated to a Civil War site. In the small woods sur­round­ing this park, the cicadas swarm in enor­mous num­bers. They cover some of the trees and swarm back and forth. At night, they seem to con­gre­gate around street lamps and are even busier than dur­ing the day. So far they’ve been nois­i­est in the morn­ing, and have been the first thing I’ve been hear­ing upon wak­ing for the past few days.

The first one I saw was exactly one week ago. This was him:

First Cicada

One of the more inter­est­ing things about the peri­od­i­cal cicada is its life cycle. The insect hatch under­ground and live there for thir­teen or sev­en­teen years, before emerg­ing in large num­bers for only a short time to mate and restart the cycle. This is part of a tac­tic called “preda­tor sati­a­tion,” which means that pop­u­la­tions of preda­tors which nor­mally have to live with­out cicadas can only eat so many until they are full, so the vast major­ity of cicadas are left alone.

The curi­ous thing is that the cicadas’ time under­ground, no mat­ter the species or the brood, is always a prime num­ber. This Brood spent sev­en­teen years under­ground and was last seen in 1996. Prime num­bers have a spe­cial prop­erty in math­e­mat­ics, in that they nat­u­rally avoid the syn­chro­niza­tion of cycles. For exam­ple, they are used in cryp­tog­ra­phy to gen­er­ate keys and pseudo­ran­dom num­bers. Two prime num­bers can be used to cre­ate a sequence of evenly dis­trib­ut­ed, but seem­ingly ran­dom num­bers by sim­ply adding one prime num­ber to the last gen­er­ated num­ber, mod­ulo of anoth­er, larger prime num­ber.

Another appli­ca­tion of primes is in mechan­ics where gears and cogs are typ­i­cally given prime num­bers of teeth so that any two gears will not get into a rhythm with cer­tain teeth meet­ing more than other teeth. This pro­motes much more even wear on the gears and makes them last longer. So for the cicadas, the sev­en­teen year under­ground peri­od, pre­vents their life­cy­cle from get­ting into sync with the life­cy­cle of a preda­tor. When they emerge, they emerge unmo­lested and en-mass:

The cicadas will only be around for a few more weeks, so I’m tak­ing pic­tures and videos while I can. I think I might take a sam­ple as well, but am not sure of the best way to do that.

    Last update: 02/06/2013

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