Dog Day Cicada
What you hear screaming in the trees in the summer
We are a bit too far north for the well-known “periodic cicadas”, the ones that come out in masses every 17 or 13 years to raise a ruckus. The ones that we have are the “dog day” cicadas, that come out every summer when it gets hot to yell in the treetops.
Technically, this one wasn’t on our property, but the ones that were in our yard were at the top of the cedar tree and I couldn’t reach them. This one was found dead on a trail only about a mile from the house[1], though, so I’ll take it. From head to wingtip it is about 2 inches long, which again was way too big to be photographed with the macro lens.
I’m pretty sure this is in the genus Tibicen. There is an identification key at Michigan State University, and the ones we have around here mostly sound like Tibicen canicularis, but this one has a smoothly-colored underside, while the picture on the above ID page shows a broad dark stripe running down the underside.
At any rate, this is one of those insects where the adult form is a minute fraction of the life cycle. The nymphs spend years underground living off of sap that they suck from tree roots, until they get big enough to dig out and metamorphose into the winged adults. They then live for maybe a week or two while the males make a tremendous racket to draw the females to them[2].
I’d always wondered how the males avoid getting eaten right away. Here they are, this huge, juicy morsel, advertising “Here I am!” at high volume for hours at a time, how could they not be eaten? If the Wikipedia page is to be believed, it is possible that they are just so loud that the birds can’t stand it, and so they mostly get left alone. They are reported to get up to 106 decibels, which is not strong enough to cause immediate physical damage to the ear, but is certainly enough to be pretty annoying close-up.
They make the noise by vibrating tymbals on the sides of their abdomens, just behind the rearmost legs. Unfortunately, this is one of the species where they are covered, so you can’t really see them here. Both the males and females have them, but the females don’t use them for making noise. Instead, they use them as ears [3]. This kind of brings up the question of whether the tymbals are ears that evolved into noise-producing organs, or they are noise-producing organs that evolved the ability to hear sounds. I’m thinking the first is more likely, since it does the males no good to make noise if the females can’t hear them, although it is possible that the females originally had some other type of sound sensor.
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[1] The trail that we were hiking on was a good 5 miles from the house by road, but that’s only because of the bridge. We are on one side of the Portage shipping canal, and the trail was behind the county fairgrounds, on the other side of the canal. You can see our house from the trail, if you can find a spot where trees aren’t in the way. The cicada was just lying beside the trail in the sand, dead as a doornail and completely undamaged. Although, if Sam had got hold of him at the time, I doubt he would have stayed undamaged for long.
[2] I had thought that the adults didn’t have functioning mouthparts, but after posting this originally, I was told that, in fact, they can and do eat as adults. My mistake. It just goes to show that even things that I think I’ve “known” since I was a kid should be double-checked. At any rate, the ability to eat probably doesn’t do them a lot of good. Tree sap is not very nutritious, and flying around or screaming at 106 decibels takes a lot of energy. That’s evidently a big part of the reason why they take so long to mature: they need the time to concentrate the nutrients enough to build up their fat reserves to use when they grow up.
[3] There are some cases where human ears can make noises, too (see this Straight Dope article, for example.) Some people evidently have muscle spasms in their ears that make their eardrums vibrate, making a noise that other people can sometimes hear from a short distance away. It is one of the forms of “objective tinnitus”, when a person hears a noise that is actually being produced in or near the ear. This is distinct from the much more common “subjective tinnitus”, where you hear a sound that isn’t actually there.
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Just wondering, but do you have trouble with your dog going nuts and trying to eat the empty cicada shells when the young ones molt? Apparently, to my friend’s Old English sheepdog, they’re a great delicacy. Or maybe she just loves eating crunchy things.
We actually are too far north for the 17-year cicadas that come out in “plagues” elsewhere. The “dog day” cicadas kind of emerge in bits and dribbles one or two at a time, so we don’t see them “in the flesh” all that often. I doubt that our dogs have found any of the shells to eat. Although, considering what other things they eat, they’d probably enjoy them given half a chance.
I was looking for pictures before it grew the wings and got big. I think I found a baby one. It’s very slow and clumsy,keeps falling over the “face” looks and exactly like the little one sitting(crawling)on my coffee-table.Please let me know the twins and I are wondering if that is what we are looking at!?