Do cicadas spend seven years underground before emerging?
Dear Straight Dope:
I just found the first cicada larvae emerged from the ground a couple of days ago here in New Mexico (the first one I've seen this year), and now I hear them buzzing in the trees. I'm wondering if the stories I've always heard about them are true. Do they really spend seven years underground as larvae, just to emerge and get one season to fly and buzz and mate? Kind of a bummer. Anyway, I'm wondering if this is true of all cicadas, or just the ones found in the east?
It sounds like someone gave you a bum steer, if they said 7 years, because the most infamous cicadas are the "periodical cicadas" (the genus Magicicada), those with a 17-year or 13-year life cycle. That's not to say there aren't some with a 7-year life cycle (there are dozens of cicadas in the US with life cycles from 2-9 years or so, varying with species and with environmental conditions), but they're wimps compared to the Magicicada species. There are six Magicicada, three that are mostly northeastern (with 17-year cycles), and three that are mostly southeastern (with 13-year cycles), and what you have there in New Mexico is another type altogether, probably an Okanagana species.
Regardless of species, all cicadas feed as nymphs buried underground on tree roots (meaning their diet is almost pure water, which is one big reason they develop so slowly), and then have a very brief non-feeding adult stage that survives at most a few weeks, only to reproduce (inserting eggs into twigs; the nymphs drop to the ground after they hatch) and die. The males sing their songs to attract females, by clattering a pair of plates over the openings to a resonant air chamber in the abdomen. Each species sings a different song, which is useful considering that you normally will find 2-3 species that overlap in a given area.
At any rate, it may be a bummer to spend 13 or 17 years sucking on a tree root, only to die after a week or two of freedom at the end, but other organisms like century plants and many salmon have that same sort of reproductive strategy (called "semelparity") and it works--you saturate your potential predators so that they can't possibly eat every one of you before you've had a chance to pass on the ol' genome and start the whole thing all over again.
Good answer! But you didn't say how long New Mexico Okanagana cicadas stay underground (by the way, I like the Magicicada name much better)? When we found that first larvae, I took my daughter outside and had her listen to how silent it was outside in the early evening. We took the grub inside and watched it transform into a cicada over the next few hours. The next evening, the air was buzzing outside with adult cicadas! I told her that the one we found would lay eggs and the babies wouldn't emerge from the ground until she was fifteen. So how old will she really be?
Uh, she's seven now.
SDSTAFF Doug replies:
I haven't heard of any research on the life cycle of Okanagana--and there are two or three other genera that could be in your area, also probably unknown. Tell your daughter the truth about how science works--there are lots of things about the natural world, especially regarding insects, that no one knows because no one thinks it's important enough to pay someone to figure it out. It's amazing how much of the field of entomology is stuff learned just because someone pursued their own curiosity at their own time and expense, rather than being paid to do it.
Well, I do, Doug. And I am going to find out.
SDSTAFF Dex interjects:
Jill, you think it's important enough to pay someone to find out?
No, dammit. I saw a cicada egg fall to the ground, I saw where the larvae burrowed into the lawn, and I ain't moving till it comes out. So I'll see you all in either 2002 or 2016. Somebody's gotta do it.