Here is a handsome example of a Brood X cicada, after emerging from its hole underground (second photo) of seventeen years. These “periodical cicadas” are the insects that spend the longest amount of time developing from egg to adult. And their history is fascinating.
The European settlers who came to North America were reminded of locusts – á la the Biblical pestilence – when they observed the droves of cicadas that abruptly emerged from the ground. But cicadas don’t fly far, and normally don’t eat plant tissues. Rather, they live underground for years consuming the sap of plant roots until they emerge in vast numbers (as many as 1.4 million per acre), shed their nymph forms to become adults, and chirp their mating song before they reproduce and die a couple weeks after.
The 17- and 13- year-cycle cicadas branched off from their genetic ancestors 1.5 million years ago during the Pleistocene epoch, a period of cooling temperatures. One scientific theory as to why these cicadas may have developed this way is that these insects could have taken advantage of a more steady-temperature phase underground as juveniles. The great numbers that come up from the earth all at once might have been nature’s way of risk management, because predators might have been overwhelmed by their numbers — at least enough to ensure a sizeable success rate of reproduction of the brood as a whole.
The seventeen-year cycle can sometimes be offset with unusual climate patterns, throwing off by about four years their usual time frame. And although scientists think that the cicadas can tell the season by the changes in plant sap, they still do not know how these insects remember the number of years gone by or know when it is time to surface for mating.
Source(s): _Scientific American_, “Brood X Cicadas Are Emerging at Last,” May 10, 2021, Kate Wong and Cherie Sinnen.
