Having been treated to the phenomenon of the periodic cicadas, we became more aware of our so-called annual cicada—for which a far smaller number emerge each year, starting in early July. These critters stay underground sucking on tree roots for only 2-5 years. Every summer a portion of them surface, live for about a month, mate, and die. The female digs holes in the bark of twigs (with her ovipositor) and deposits eggs. Nymphs hatch from the eggs, fall to the ground, and tunnel downwards—waiting patiently for a few years (not 17!), before coming up again.
When it’s time for their coming out party, the nymph peeks out at night (probably can’t take the bright sun after so long in the dark), crawls up a tree, and latches on with its spiky feet. Its shell (exoskeleton) splits open down the back and the adult cicada slowly squeezes out over the next couple of hours. We were treated to this amazing display a few days ago (see accompanying photos). Like watching the minute hand on a clock—you can’t really see it moving, but do notice a change in position over several minutes—the adult slowly extruded itself from the nymph’s shell. The most amazing thing was watching its wings unfold from tiny green nubbins to long, graceful, diaphanous appendages.
When the adult first squeezes out, it is soft and pale. Every so often its body gently shudders or its wings slightly twitch, but otherwise it’s motionless. I kept wondering if it was able to register the presence of these two monstrous beings peering fixatedly down at it and exclaiming, “Oh, look at that!” As it began to dry out, it darkened and its new exoskeleton began to harden. As we watched the insect slowly expand, we marveled at how it once was able to fit inside that cramped shell. It was kind of like the crowd of clowns I once saw emerge from the circus’s tiny Volkswagen.
Over the next few weeks the males will blare out with that penetrating, whining song. They tend to stay hidden in the trees, so we seldom see them. That’s why, as a child, I was easily fooled into thinking that it was vibrating wires making the racket. (Well, maybe I was a little gullible.) Their call is a high-pitched and rapidly pulsating song that begins softly but builds to an irritating whine that lasts for a minute or so. Often several males will join in a synchronous chorus and you can hear their swelling sound waft through the forest like a slow-moving breeze. On the hottest days their song is continuous, all the bloody day long, as if they were complaining about the heat.
Cicadas, although they appear menacing, are harmless if picked up. They can’t bite or sting. They possess a feeding tube that they poke into a tree branch and suck up some moisture (hence they are more related to aphids than leaf-chewing crickets and katydids).
If the male’s singing is successful, he’ll mate, the lady will lay her eggs, the tiny babies will drop to the ground, burrow down to a nutritious tree root, and begin counting the days to freedom again—either 730, 1095, 1460, or 1725 days (2, 3, 4, or 5 years). Amazing little mathematicians! At least they don’t have to count off 6205 days, like the periodical cicadas do! I think hidden within that tymbal must be a tiny abacus, with which they keep count.
Thursday, July 22, 2010
Tuesday, July 20, 2010
Friday, July 16, 2010
Blaring Whiners—Part 1
We are entering the heart of summer—those hot and humid days when the sweat flows freely and frequently, and noisy insects dominate the acoustical environment. All night long the crickets and katydids chirp away—providing a constant droning chorus of sound by rubbing various body parts (wings and legs) together. Their songs are trills, squawks, buzzes, and sometimes even pleasant bell-like tones.
The daytime sound field, however, is dominated by cicadas—incredibly loud noisemakers who are biologically unrelated to crickets and katydids. Their sound-producing mechanism is also dissimilar: located on the bellies of male cicadas are tymbals (even the name tymbal sounds garish), which are drum-like organs that vibrate by the contraction of his tummy muscles. The sound is amplified by resonators and membranes built into his gut, to produce a penetrating noise that would be envied by any heavy-metal guitar player who loves the shrillness of electronic distortion.
When I was a kid I would hear this piercing whine on hot summer days. It was so loud that I’d stop playing and look around, wondering what in the world that could be. An older kid told me that it was coming from the hot wires strung between telephone poles. I believed that tale for many years.
Three years after we moved out here to the country, we had an invasion of periodical cicadas. In our neck of the woods this incursion is expressed by the Linnaeus periodical cicada—often popularly and improperly dubbed 17-year locusts, because countless hordes emerge every 17 years and fill the air with their drone for a few weeks. About two inches long and sporting bulging bright red eyes, the periodical cicadas are a rather grotesque sight, and the woods echo with their hum. A few days after the invasion began, our dogs caught on to the fact that these bugs were a tasty source of protein and we’d laugh to see them dash across the yard and leap into the air to catch and consume one.
An amazing fact about these periodic cicadas is that in their nymph stage they remain buried underground, sucking on tree roots for 17 years. Then they all emerge within a week of each other. How do they count up all those years so accurately? Aren’t there a few who miscalculate and emerge at 16 or 18 years? Can you imagine their confusion, if they did? “Where is everybody?” It’s just another of nature’s wonders.
The daytime sound field, however, is dominated by cicadas—incredibly loud noisemakers who are biologically unrelated to crickets and katydids. Their sound-producing mechanism is also dissimilar: located on the bellies of male cicadas are tymbals (even the name tymbal sounds garish), which are drum-like organs that vibrate by the contraction of his tummy muscles. The sound is amplified by resonators and membranes built into his gut, to produce a penetrating noise that would be envied by any heavy-metal guitar player who loves the shrillness of electronic distortion.
When I was a kid I would hear this piercing whine on hot summer days. It was so loud that I’d stop playing and look around, wondering what in the world that could be. An older kid told me that it was coming from the hot wires strung between telephone poles. I believed that tale for many years.
Three years after we moved out here to the country, we had an invasion of periodical cicadas. In our neck of the woods this incursion is expressed by the Linnaeus periodical cicada—often popularly and improperly dubbed 17-year locusts, because countless hordes emerge every 17 years and fill the air with their drone for a few weeks. About two inches long and sporting bulging bright red eyes, the periodical cicadas are a rather grotesque sight, and the woods echo with their hum. A few days after the invasion began, our dogs caught on to the fact that these bugs were a tasty source of protein and we’d laugh to see them dash across the yard and leap into the air to catch and consume one.
An amazing fact about these periodic cicadas is that in their nymph stage they remain buried underground, sucking on tree roots for 17 years. Then they all emerge within a week of each other. How do they count up all those years so accurately? Aren’t there a few who miscalculate and emerge at 16 or 18 years? Can you imagine their confusion, if they did? “Where is everybody?” It’s just another of nature’s wonders.
Wednesday, July 14, 2010
Sunday, July 11, 2010
Native Versus Non-native
We frequently hear the terms “native” or “indigenous,” referring to a people or a plant or an animal that are native to a place—i.e., were born or originated there. These terms are often used in conjunction with the contrasting or opposing terms “non-native” or “invasive.” In the deep past the migration of species was so slow that all living things were pretty much considered native, but now we humans are in constant and rapid movement throughout the world, taking countless flora and fauna with us, so that native species are continually encountering non-native competition—sometimes with tragic effects.
A native species is one that originated in a given location. It came into being (the root of the word native is the Latin word natus, born) in its indigenous place; it evolved there. In the evolutionary process, species last only if they find a niche and come into balance with many other species; i.e., settle into a complementary existence. Over time an equilibrium is reached, and if the environment remains stable for a while, the various native species maintain that cooperative network, wherein each of them fulfills a useful role.
A non-native species—once indigenous to its own locale—is one that migrates to a foreign place. It then finds itself in strange territory, looking for a niche to occupy. In doing so, usually one of three outcomes will happen: (1) it can’t fit in or compete and dies out, (2) it finds a niche and settles in (sometimes adapting and changing itself and its new home in the process), or (3) it enjoys a considerable advantage in its new locale (finding little competition there) and it runs amok. The third case is the one that often gets labeled “invasive species,” because it moves in, upsets the delicate balance, and takes over. Some examples of invasive species in the US are kudzu vine, gypsy moths, Dutch elm disease, house wrens, avian influenza, water hyacinth, zebra mussels, etc., etc.
This process of native and non-native species competing with each other is as old as life itself. Species have always migrated into new territory and found themselves competing against native critters. The difference lately is that the migration rate can now be at the speed of an airplane. Think of the recent worldwide spread of swine flu.
Thus indigenous species are constantly and suddenly being exposed to strange invaders, often at a very bad time for many of them: when their native environment is already under stress and being degraded. Even in the quite recent past species had the leisure of many thousands of years to adapt to the changes in their environment or the encroachment of competitive species. Now they are being assaulted far more often and being forced to deal with these changes in days and months, rather than eons.
One of the most threatening invasive species on Earth is Homo sapiens. We are indigenous only to Africa, yet we have spread to every corner of the globe—overnight in nature’s time scheme. In every case we’ve bested any native species we’ve encountered, driving many of them to extinction. The Americas once were home to dozens of mega-fauna species (mammoths, ground sloths, giant bears, etc.), that disappeared soon after humans arrived on these continents, thousands of years ago. Passenger pigeons once blackened the skies above North America, until people shot them into oblivion, a century ago. Australia was home to several species of giant flightless birds, until people migrated there, 45 thousand years ago and found them easy pickings. The list could go on for pages.
We humans have relentlessly altered our environment, often by rooting out native plant species, as we create vast areas of cultivated products. Some would say that this most invasive species of all is running amok. In every case in the past, when an invasive species has exploded its population far beyond a sustainable level, nature has eventually forced things back into balance. The invaders’ numbers precipitously crash—think invasions of locusts. The gypsy moth relentlessly marched south from New England in the 19th century, rapaciously attacking and killing native oak trees, until it finally got checked by a native species of fungus in the Middle Atlantic states, just a few years ago. The crash of an out-of-balance non-native species seems inevitable. I wonder what Mother Nature has in store for Homo sapiens.
A native species is one that originated in a given location. It came into being (the root of the word native is the Latin word natus, born) in its indigenous place; it evolved there. In the evolutionary process, species last only if they find a niche and come into balance with many other species; i.e., settle into a complementary existence. Over time an equilibrium is reached, and if the environment remains stable for a while, the various native species maintain that cooperative network, wherein each of them fulfills a useful role.
A non-native species—once indigenous to its own locale—is one that migrates to a foreign place. It then finds itself in strange territory, looking for a niche to occupy. In doing so, usually one of three outcomes will happen: (1) it can’t fit in or compete and dies out, (2) it finds a niche and settles in (sometimes adapting and changing itself and its new home in the process), or (3) it enjoys a considerable advantage in its new locale (finding little competition there) and it runs amok. The third case is the one that often gets labeled “invasive species,” because it moves in, upsets the delicate balance, and takes over. Some examples of invasive species in the US are kudzu vine, gypsy moths, Dutch elm disease, house wrens, avian influenza, water hyacinth, zebra mussels, etc., etc.
This process of native and non-native species competing with each other is as old as life itself. Species have always migrated into new territory and found themselves competing against native critters. The difference lately is that the migration rate can now be at the speed of an airplane. Think of the recent worldwide spread of swine flu.
Thus indigenous species are constantly and suddenly being exposed to strange invaders, often at a very bad time for many of them: when their native environment is already under stress and being degraded. Even in the quite recent past species had the leisure of many thousands of years to adapt to the changes in their environment or the encroachment of competitive species. Now they are being assaulted far more often and being forced to deal with these changes in days and months, rather than eons.
One of the most threatening invasive species on Earth is Homo sapiens. We are indigenous only to Africa, yet we have spread to every corner of the globe—overnight in nature’s time scheme. In every case we’ve bested any native species we’ve encountered, driving many of them to extinction. The Americas once were home to dozens of mega-fauna species (mammoths, ground sloths, giant bears, etc.), that disappeared soon after humans arrived on these continents, thousands of years ago. Passenger pigeons once blackened the skies above North America, until people shot them into oblivion, a century ago. Australia was home to several species of giant flightless birds, until people migrated there, 45 thousand years ago and found them easy pickings. The list could go on for pages.
We humans have relentlessly altered our environment, often by rooting out native plant species, as we create vast areas of cultivated products. Some would say that this most invasive species of all is running amok. In every case in the past, when an invasive species has exploded its population far beyond a sustainable level, nature has eventually forced things back into balance. The invaders’ numbers precipitously crash—think invasions of locusts. The gypsy moth relentlessly marched south from New England in the 19th century, rapaciously attacking and killing native oak trees, until it finally got checked by a native species of fungus in the Middle Atlantic states, just a few years ago. The crash of an out-of-balance non-native species seems inevitable. I wonder what Mother Nature has in store for Homo sapiens.
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