I traveled to Iowa this week (more on that next week) and just happened to arrive during the emergence of one of the world’s most intriguing insects – the periodical cicada (Magicicada sp). Made up of seven different species, periodical cicadas are found only in eastern North America and are named for their long life cycles of either 13 or 17 years.
All cicadas (that I know of) spend most of their lives underground as larvae before emerging for a brief, noisy life aboveground. What makes periodical cicadas unique is not so much the length of time spent as larvae – though it’s longer than other cicada species – but rather the synchronization of their emergence. The common dog-day cicada, for example spends multiple years underground as a larva, but we see adults every year because their emergence is staggered across years. In contrast, periodical cicadas synchronize their emergence so the entire population in a particular area is on the same schedule. That timing of emergence, however, does vary by region across North America, so while seventeen-year cicadas are out in Iowa, Illinois, and Missouri this year, they emerged last year in an area covering states including Maryland, New York, and Virginia. People living in eastern Nebraska will get a chance to see them in 2015.
Emerging as adults in hordes probably helps ensure the survival of individual periodical cicadas (and their species) because predators can’t eat nearly enough to put a dent in the population. If periodical cicadas showed up in huge numbers every year or two, there would surely be predators with life cycles timed to take advantage of the abundant food source. However, the extreme length and synchronization of the cicada life cycle has apparently kept any predator species from being able to take advantage (evolutionarily) of the phenomenon. Fortunately for us, cicadas are harmless to people, and even the damage they do to trees by feeding and laying eggs in stems is almost always temporary.
There is much more fascinating information about periodical cicadas, but others have already covered it far more completely than I can. If you’re interested, I strongly encourage you to visit the magicicada.org to learn more.