A non-plague of non-locusts

egg-laying cicada

The locusts are, it must be said, a bit of a plague on the locusts. The males call “Pha-roah! Pha-roah!” in a slow southern drawl while the females plunge their scimitar-shaped ovipositors into the thorny twigs, sometimes so deep that they break. All along the top edge of the field, the black locusts are acquiring a pruned and chastened look, as if they were the victims of some very localized storm.

cicada damage

Of course, 17-year “locusts” are really cicadas (see Brood XIV). According to some sources, when early European settlers first encountered periodical cicadas in eastern North America, the only parallel they could think of for such an extreme insect outbreak was the plague of locusts in the Bible, so “locusts” they became — despite the fact that, as members of the order Homoptera, they could scarcely be more distantly related to true locusts, which are grasshoppers, Orthoptera. According to the Locust entry in the Wikipedia, however, the conflation goes much further back, to “the Vulgar Latin locusta, which was originally used to refer to various types of crustaceans and insects.” The English essayist Thomas Browne was bemoaning the confusion between locusts and old-world cicadas as early as the 17th century. And obviously the popular description of the call of Magicicada septendecim as “Pharoah” shows the unabated influence of Exodus 10:4-15.

However, it would be a great exaggeration to say of these “locusts” that “they covered the face of the whole earth, so that the land was darkened; and they did eat every herb of the land, and all the fruit of the trees which the hail had left: and there remained not any green thing in the trees, or in the herbs of the field, through all the land.” Here’s what the folks at Cicada Mania say:

Question: Will the cicadas kill my trees, shrubs and flowers?
Answer: Possibly. Cicadas don’t kill flowers and shouldn’t damage shrubs, but they can do damage to young, wimpy trees like ornamentals. If you have wimpy little trees, you can net them to keep the cicadas off. Tree species that aren’t native to North America won’t fare as well as native species. Trees that lose a lot of branches typically revive after a year or two, but they will be ugly in the mean time. Cicadas actually are a benefit to trees, as they destroy the weaker branches. Please don’t use pesticides — you’ll destroy the good bugs as well as the “nuisance” bugs, and ultimately do your garden and the environment a huge disfavor.

Of course, as larvae, cicadas do subsist on tree sap, but given that cicadas and deciduous trees have evolved together, I doubt that they do much to weaken the trees. Though the science is inconclusive, it’s likely that their extensive tunneling benefits the trees by aerating the soil, and possibly by creating macropores for new roots and fungal mycelia. An AP article quotes a Dr. Frank Hale from the University of Tennessee:

The holes from which they emerge aerate the soil around the tree roots, Hale said. The millions of decaying cicada bodies supply nitrogen and other nutrients, which rain washes down the holes to the tree roots.

However, a Penn State Ag School publication for orchardists assumes the worst, and considering the unique stresses on heavily pruned and sprayed trees in monocultural plantations, it may well be on-target with its recommendation to prevent egg-laying at all costs. It also emphasizes netting if feasible, and mentions the harmful effects of pesticides on beneficial insects.

cicada in scrub oak

Do the various Magicicada species vary in their arboreal preferences? I’ve mentioned black locusts as a favorite for swarming and egg-laying activity (see my video at the Plummer’s Hollow blog), but I suspect that’s largely because of their location in the field-forest ecotone. The cicadas here do show an affinity for forest edges and openings, regardless of where they originally emerged. I don’t know if the fact that locust trees are nitrogen-fixing legumes makes them any more attractive as adoptive mothers to cicada larvae. We have noticed relatively few cicadas in the black walnuts that surround the main house, which might seem logical given the toxicity of walnut roots to many other plants, but it seems that if we had the rarer third species, Magicicada septendecula, that might not be the case:

Within the same brood, the three species are always perfectly synchronized, but they are separated microspatially by having different habitats within the same woodland. Magicicada septendecula prefers ovipositing in hickories and walnuts, and emerges in higher proportions under those trees than under comparable oaks. Both M. septendecim [the “Pharoah” species] and M. septendecula occur together in upland woods, but septendecim exhibits much less host specificity than septendecula. The latter species is much rarer than septendecim; it can usually be heard chorusing in local patches within a woods occupied by septendecim. Magicicada cassini is a species of floodplain woods, and characteristically can be seen to replace septendecim and septendecula as one moves down a wooded slope leading to a stream. Over much of the eastern United States, however, the original forest has been extensively disturbed. Periodical cicadas survive and reproduce surprisingly well in cutover, scrubby second growth. Tree species characteristic of floodplains, like American elm, are often a component of upland second growth, and, especially in such situations, cassini, septendecim, and septendecula become intermixed though they remain reproductively isolated. The present lack of microspatial separation in many situations, then, is an artifact of human disturbance.
—Henry S. Dybas and Monte Lloyd, “The Habitats of 17-Year Periodical Cicadas (Homoptera: Cicadidae: Magicicada Spp.),” Ecological Monographs, Vol. 44, No. 3 (Summer, 1974)

That might explain why the M. cassini cicadas are so much louder and more numerous around Canoe Creek State Park, much of which is floodplain or early-succession second growth. At our annual Audubon Society picnic last week, they were nearly deafening. In fact, a friend just told me that the dog-day cicadas are usually very numerous there, too — and regardless of the species, they make excellent fish bait, he said. Hardly the stuff of plagues.

Today is the deadline to submit links to the next Festival of the Trees. Details are here.

11 Replies to “A non-plague of non-locusts”

  1. It still doesn’t explain (to me at least) why they are in Bellefonte and not State College. Or moreover, why they are only in certain parts of Bellefonte. The tree species, I suppose, is what you are referring to here. They destroyed some of the branches on our Macintosh, but they mostly occupy a large oak tree in the backyard. (I’m not entirely sure it’s an oak. I’ll take a look tomorrow.) But they’re also in my butterfly bush and our grape vines. What gives?!

    Update: I am no longer afraid of them. I’ve turned in my fear for pure fascination. Now I pick them up at every opportunity. Interesting fact: If I pick one up by the wings and it makes its noise-maker defense sound, another will fly at me, as if to rescue the captured cicada. These guys are amazing.

  2. Nice cicada post and photos, Dave! I’ve witnessed several cicada eruptions; the insects can cause appalling damage to young trees, but most of them will recover during the 13-or-17-year interregnum.

  3. G.M.: They were logging in “my” holler (I rent a house in a 300 acre hollow in central KY) during the cicada bloom. When the loggers started up their chainsaws and skidder in the early morning in the log yard (an empty field), the cicadas came flocking in, looking for those really big fellas, I guess. In the case of your captive cicada, I suspect the one flying in was more interested in breeding than rescue. During the height of the breeding I saw two locked together on the ground, while a huge beetle was consuming the abdomen of one of them. Circle of life… rb

  4. Gina Marie – Macrospacial differences in brood occurence may be due to happenstance – we’re basically on the border between different broods here – or on broader land use patterns. In areas where trees are few and starlings are many, for example, it may be difficult for enough cicadas to survive to reproduce, leading to local extirpations. Who knows?

    Glad you got over your aversion to them!

    Larry – Glad you liked the post. Yeah, I guess you must be close to some 13-year broods in Hannibal. We don’t have any here. But in the warmer areas where shorter-cycle Magicicadas are found, the trees grow more quickly, so again, as you say, damage is minimized over time.

    arby – Great stories about the chainsaws and the mating! I sure wish you had a blog. Your comment about fruit trees on an earlier post was one of the things that sparked this post.

    Lee’s River – Yes, except that they don’t actually stridulate, as Gina’s video demonstrates. The Wikipedia article, though lacking in other respects, is good on this:

    Male cicadas have loud noisemakers called “timbals” on the sides of the abdominal base. Their “singing” is not the stridulation (where two structures are rubbed against one another) of many other familiar sound-producing insects like crickets: the timbals are regions of the exoskeleton that are modified to form a complex membrane with thin, membranous portions and thickened “ribs”. Contracting the internal timbal muscles produces a clicking sound as the timbals buckle inwards. As these muscles relax, the timbals return to their original position producing another click. The interior of the male abdomen is substantially hollow to amplify the resonance of the sound. A cicada rapidly vibrates these membranes, and enlarged chambers derived from the tracheae make its body serve as a resonance chamber, greatly amplifying the sound. They modulate their noise by wiggling their abdomens toward and away from the tree that they are on. Additionally, each species has its own distinctive song.

  5. That’s a great post. Here in southwestern Ohio, things are dying down (and off, thank goodness!).
    Thank you SO MUCH for bringing up the pesticide and native tree issue. Too many people just grab a bottle of chemical gunk and don’t think about the consequences.
    In 2004, we saw zero cicadas here on our property, but this year….well, they reached “biblical” proportions. None in the black walnuts, but all over our downy hawthorn, our Bradford Pear (which I have been doing voodoo dances around trying to kill it). Our neighborhood is young, but we are on the edge of it, next to a mature woodland, so LUCKY US.
    : )

  6. Hi Susan – Glad you found the post useful. That’s interesting that your black walnuts are cicada-free, too, even at such high levels of cicada population density. And thanks for reminding me to check our own Bradford pear, which stands out in the middle of the field – though I think I’m probably a bit late now! It could use a good pruning, though. (Can you tell I’m a neglectful gardener?)

  7. I have only seen the irruptive cicadas once, years ago in Princeton, NJ. We never had them in the midwest where I grew up and I don’t have them on the mountain. They must be very selective. We do have a few of the seasonal summer cicadas.

  8. bevson – “Irruptive,” eh? No one would ever guess you’re a birder. :)

    They’re certainly not everywhere, even in their historical range. Just because something is incredibly common doesn’t mean it isn’t vulnerable, as the examples of the now-extinct Rocky Mountain locust and passenger pigeon should serve to remind us.

    CGP – Glad you found my cicada blogging to be of interest. I was worrying it might seem a tad excessive!

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