A non-plague of non-locusts

holloway overhung with ancient trees n Cornwall

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.

The shortest night

holloway overhung with ancient trees n Cornwall

top-heading garlic

The morning after the summer solstice, which arrived just before 8:00 p.m. here, the garlic tops have each coiled another half-turn. Irises that were once blue dangle curled brown locks and raise flags of surrender, milky as a blind man’s eyes. It’s chilly. I grab my hooded sweatshirt off the doorknob and stand staring for a moment at my reflection in the bald brass.

cicada wings1

A 100-foot section of the mowed path leading from the garage into the woods is bejeweled with cicada wings, hundreds upon hundreds of them, covered with dew and glinting in the morning sun. What brought them there?

They had to have been brought: it’s not an area where either the emergence or the courtship of the 17-year cicadas have been particularly intense, or indeed noticeable. There are no overhanging branches from which birds might have discarded the wings as they ate — in fact, the wings peter out as soon as small trees begin to line the trail.

I suspect raccoons. What else could it be? I can picture them gathering there in the light of the just-past-full moon, squatting companionably as they pull the wings off their squirming victims and chew, chew, chew.

Brood XIV

holloway overhung with ancient trees n Cornwall

17-year cicada

Walking into the house after dark, I snap on the light and notice a thumb-sized lump under my shirt, right above my navel. It’s moving, though I don’t feel anything. I lift the shirt and there, clinging to the other side of the green cotton, is a periodical cicada. I pull it off, carry it outside and give it a toss. A dry rattle as it flutters off into the night. Maybe those strange red eyes can see in the dark.

For seventeen years — an eternity for most insects — they’ve been living completely in the dark, the cicadas of Brood XIV. Silent, wingless, and pale as ghosts they have burrowed from root to root, sucking on the milk of trees. Then in late April they began to experience subtle changes in their bodies, growing new muscles, and feeling a sudden strong urge to burrow upwards. Rather than push the dirt behind them like a mole or pass it through their bodies like a worm, their powerful forelegs pushed and compacted the newly thawed earth into half-inch cylinders as they climbed.

They dug to within an inch or less of the surface, making visible mounds in the mud and leaf duff in wetter areas. Skunks and other predators dug some of them up, and for weeks we were puzzled by what turned out to be dried sections of their bore-holes scattered all over our trails. My mother took to collecting these strange artifacts in a shoebox in her study; we couldn’t remember ever seeing anything like it. If we weren’t such rationalists, we might’ve thought the Little People were taking a crash course in pottery.

periodical cicada tubes

The nymphs sat in their burrows and waited for the onset of warm nights, a wait that might have lasted only a couple weeks some years, but this year — THE year, as far as they were concerned — it was closer to six. Four days ago I saw my first red-eyed cicada on a dead raspberry cane and realized that the emergence had begun.

Yesterday — the morning after I carried a cicada in under my shirt — I waded slowly through the thick air of our first heat wave since last April, up to the crest of the ridge above my house and southwest along the trail. It sounded as if our closest neighbor in the valley were operating some kind of machinery, I thought, but couldn’t quite figure out what — an eerie metallic buzz. Then I realized: it’s them. They’re here! I picked my way down to where the slope turned steep, but still the sound was below me, coming from an open area that had been logged about a decade before. The sunny, southeast exposure must have led the cicadas there to emerge earlier than those elsewhere on the mountain.

It occurred to me that there might be some activity on the powerline right-of way. I always associate powerlines with cicadas, in part because their calls have such an electronic quality. But in fact because the powerline opening is several degrees warmer than the surrounding woods, the night before last had indeed been a scene of mass ecdysis there, the nymphs emerging from their burrows, crawling a foot or two up into the vegetation, and climbing right out of the center of their wingless thoraces. By dawn, all would’ve darkened from white to bluish gray with red-veined wings. When I arrived on the scene at mid-morning, nearly every lowbush blueberry and scrub oak shrub was dotted with adult cicadas, and some of them were beginning to take short, clumsy flights, like remote-controlled toy airplanes piloted by inexperienced hands.

I found one two-foot-tall scrub oak as heavily ornamented as a Christmas tree. When I squatted with my camera for a closer look, I noticed the translucent brown larval shells, or exuviae, clinging to the undersides of the leaves. I couldn’t help thinking that whatever whacked-out evangelical preacher first dreamed up that Rapture business must’ve witnessed a 17-year cicada emergence.

cicada exuviae

By this afternoon, I was beginning to hear them from the treetops right outside my door. I walked back up to the powerline to see if I could find any singing at close enough range to film, but they’d all moved on — up into the treetops, I suppose. I also noticed, however, an alarming number of half-inch-diameter holes stippling the ground almost everywhere in the woods — there must be few species of native trees they don’t patronize. The ecological consequences of their aeration of the forest soil must be immense.

Things are going to get pretty loud here in the coming days, I think. As the aforelinked webpage puts it, “Soon after emerging, males begin their constant ‘singing’ while females remain silent. The sound made by adult males is sometimes haunting and eerie.”

After around ten days of cacophony and orgiastic mayhem, the females will begin laying their eggs and the next cycle of this longest-lived of North American insects will begin. Rather than sow their seeds in the earth, as one might expect, they instead plant them in the treetops, long ovipositors slicing like harrow blades into the twigs of trees and shrubs from nearly 80 different species. Each female lays some two dozen eggs per slit, and repeats the process until all her 400-600 eggs are gone. Where two weeks before, the adult cicadas emerged from slits in the backs of their former selves, now they insert their future offspring into slits cut into what will become their nurse-trees.

The true opposite of ecdysis, I suppose, is death, and a month from now the ground should be littered with cicada carcasses. By the time the white, ant-sized cicadas hatch in late August and drop to the ground, most traces of their parents should be gone.

Needless to say, birds, squirrels, and virtually every other macrofaunal inhabitant of the forest will have a heyday, feasting on this almost literal fat of the land. Early European settlers in eastern North America marvelled at the teeming wildlife, almost all of which have by now been sadly diminished, if not persecuted to extinction, with the exception of a few superabundant pest species such as tent caterpillars and white-tailed deer. The mass emergence of the 17-year cicadas is one of the last great spectacles of its kind.

Ending expanded 6/8/08; cross-posted to the Plummer’s Hollow blog. For more on periodical cicadas — much, much more — see the Cicada Mania blog. For an MP3 of the singing, go here. And since I was just talking about nature documentaries yesterday, I’d be remiss if I didn’t mention the fine film “Return of the 17 Year Cicadas” on YouTube.