Category Archives: insects
Last August, the butterfly bush in my front garden attracted the first-ever giant swallowtail (Papilio cresphontes) to Plummer’s Hollow. Two days ago I spotted our second — a little earlier in the month and in much better condition — at the very same bush. It stayed for less than five minutes. I slowed the video to half speed; this was a very fast-moving creature, which perhaps explains how it manages to disperse so far from its larval habitat of citrus trees.
The cicada chorus starts around 6:00 in the morning now, and goes until late afternoon, letting up only in the case of rain. Sunnier areas such as forest openings and edges are definitely more attractive to the courting cicadas.
Further online research has revealed that Brood XIV, like most other 17-year cicada broods, includes three different species, of which we have at least two. In the above video, which I shot this morning at the Far Field and the top of First Field, the first-featured species is Magicicada cassini — the one with the more metallic call. My camera unfortunately wasn’t really up to the task of capturing them in flight; they were extremely active in the small locust trees. A box turtle behind the spruce grove at the top of First Field seemed slightly freaked out, but that’s probably my own projection. In reality, she was probably thinking slow turtle thoughts about where to find her next meal.
The final portion of the video shows Magicicada septendecim, which makes the weirder and more musical of the two calls we’ve been hearing. I was surprised by the low volume of its call at close range, but probably it was just getting warmed up. Notice how the abdomen moves as it “sings.” Here’s a description of what’s involved from the University of Michigan Museum of Zoology’s Periodical Cicada Page, the source of most of my information in this post:
As in nearly all cicada species, male periodical cicadas produce “songs” using a pair of tymbals, or ridged membranes, found on the first abdominal segment. The abdomen of a male cicada is hollow and may act as a resonating chamber; the songs of individuals are loud, and large choruses can be virtually deafening. Females of most cicada species do not have sound-producing organs. Both sexes hear the sounds of the males as well as other sounds using membranous hearing organs called “tympana” found on the underside of the abdomen.
Over the course of an emergence, males congregate in “choruses” or singing aggregations, usually in high, sunlit branches. Females visit these aggregations and mate there, so choruses contain large numbers of both sexes.
As a follow-up to the previous post, my mother emailed a cicada expert at the University of Connecticut named Dave Marshall for more information about the mud turrets she collected. He replied,
No one knows for sure why the cicadas build the turrets when they do. Most of the time they do not, and yet sometimes a whole area will have them built way up several inches. Theories ranges from differences in soil moisture/recent rainfall (nymphs somehow reducing the risk of drowning) to artifacts of differential exposure to light. People were writing about this 100 years ago in USDA pubs, and we have hardly learned any more since then!
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.
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.
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 mdash; 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.
Cross-posted to Via Negativa. 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.
Let their habitation be desolate; and let none dwell in their tents.
Psalm 69:25 (KJV)
Eastern tent caterpillars (Malacosoma americanum) are a common sight this time of year, especially in their last instar, after they abandon their tents. They stray onto the porches and wander over the furniture, looking for protected places in which to pupate. On a visit this past Monday, my three-year-old niece Elanor decided that they were cute — not typically my own reaction — and began petting them, prompting the caterpillars to arch their heads back like housecats. Yesterday afternoon, I watched one crawling up the neck and across the face of a box turtle, which merely shut one eye while the caterpillar took its measure.
The tents began appearing at the end of April in unusual numbers, especially on black cherry trees, which are the favorite food source for tent caterpillars and occur in unnatural abundance across Pennsylvania due to 150 years of clearcut logging practices and the reversion of old fields and pastures. Black cherry is a common first-succession tree species in many forest types, and thanks in part to its relative unpalatability to white-tailed deer, it can form almost pure stands in many areas that would have formerly hosted oak-hickory, beech-hemlock, or mixed deciduous forests. Here in Plummer’s Hollow, many of our southeast-facing slopes are dominated by black cherry stands, and I figured they’d be completely defoliated by this time.
Instead, Sapsucker Ridge is white with blossoms, filling the air with an ambrosial scent. One finds only a few black cherries as badly defoliated as the one in the second photo; the tree above is more typical. Though dotted with tents, only scattered branches have actually been stripped of their leaves.
A closer look reveals that most of these tents are filled with dead caterpillars. The few still alive twitch spasmodically. What happened? I’d guess that the unusually cold, wet weather over the past few weeks is at fault. Nighttime temperature routinely dropped into the low 40s this month, and sometimes even into the high 30s; daytime temperatures rarely exceeded the mid-50s; and rain was almost constant for the first three weeks of the month. Not only would the cold have shut down their temperature-sensitive digestive systems for prolonged periods, but the rain would have kept them confined to their silken tents, and the two together would’ve made them much more susceptible to starvation and disease. According to the Wikipedia article on tent caterpillars,
The tent is constructed at a site that intercepts the early morning sun. The position of the tent is critical because the caterpillars must bask in the sun to elevate their temperatures above the cool ambient temperatures that occur in the early spring. Studies have shown that when the body temperature of a caterpillar is less than about 15 °C [59 °F], digestion cannot occur. The tent consists of discrete layers of silk separated by gaps and the temperature in these compartments varies markedly. Caterpillars can adjust their body temperatures by moving from one compartment to another. On cool mornings they typically rest in a tight aggregate just under a sunlit surface of the tent. … Later on in the spring, temperatures may become excessive at mid day and the caterpillars may retreat to the shaded outside surface of the tent to cool down.
Entymologist Vincent G. Dethier’s wonderful and evocative classic, The World of the Tent-Makers: A Natural History of the Eastern Tent Caterpillar (University of Massachusetts Press, 1980) describes in Chaper 13 (appropriately enough) the battery of predators and diseases that keep this native insect in check. He details the spread of a deadly virus from colony to colony, then adds:
As if that were not enough the unusually wet late spring had been kind to molds, mildews, smuts, blasts, and bacteria. A particularly virulent spore-forming species of bacterium struck many of the colonies. … The enormous population of tent caterpillars had been cropped by weather, starvation, ants, bugs, parasites, fungi, viruses, bacteria, and misadventure in general. It had been a particularly trying year. Summer had hardly begun and the die had already been cast for the year to come. There would be fewer moths, fewer egg masses, and fewer colonies of the next generation.
So a spring that spells bad news for many farmers is good news for the wood products industry, which relies heavily on black cherry in Pennsylvania. Unlike fall webworms, which come too late in the season to have much of an impact on the trees they defoliate, tent caterpillars can greatly stress the trees they defoliate during their periodic outbreaks.
As global climate change plays hob with our weather patterns, it will be interesting to watch the effects on insect outbreaks, and over the long term, on forest succession. For example, if black cherries continue to predominate as many foresters would like, more-frequent icestorms would have a much greater impact than they would if less brittle species such as red oaks and tulip poplars took their place. Warm winters are said to promote the spread of pest insects, but what about warm winters followed by cold springs? I’d heard that the state was due for some pretty large gypsy moth outbreaks this summer as well, but here in Plummer’s Hollow, at least, their caterpillars are few and far between.
Cross-posted to Via Negativa.
The monarch butterfly migration is well underway, with higher numbers than we’ve seen in many, many years. With close to fifty acres of goldenrod and asters in our First and Far Fields, we get a lot of monarchs coming in to nectar and spend the night. And with nighttime temperatures falling into the 40s and 50s (5-15 C), the monarchs tend to seek each other out in late afternoon so they can spend the night in small clumps in the trees. The next morning, the fields are aflutter with hundreds of monarchs, especially bordering Sapsucker Ridge where the sun strikes first.
Anecdotal evidence suggests a robust monarch migration throughout the east. My Uncle Hal drove up from Beckley, West Virginia the other day, and said he was dodging monarchs all the way. And a post to the Pennsylvania Birding listserve on Thursday reported a staggering 7,000 monarchs in one morning at a hawk watch in Northampton County. The poster, Michael Schall, says, “It was non-stop on the clicker trying to get a decent count with my total of nearly 7000 by the time I had to leave at 1300pm conservative at best. Most were counted between 0900 and 1030 as numbers were light when I left for work.” This jibes with our impression of the greatest movement occuring in the morning.
To see what our main field looks like when the goldenrod is in bloom, click on the newly illustrated “Where and What is Plummer’s Hollow?” page and scroll down to the bottom.
Yesterday afternoon around 5:30, a very tattered giant swallowtail (Papilio cresphontes) appeared on the butterfly bush in my front garden. This was a new record for the mountain. We watched it nectaring for about ten minutes before it flew away.
The larvae feed on members of the citrus family, so this butterfly’s tattered appearance is understandable. I found the following on eNature:
Known as the “Orange Dog” by citrus growers, the Giant Swallowtail is sometimes considered a citrus pest and is subjected to massive spraying. It is capable of flying long distances and often strays into northern and midwestern districts.