Innumerable Insects

by Michael S. Engel

  PLECOPTERA

  Unlike the mayflies, dragonflies, and damselflies, almost all other flying insects have wings that can be folded backward to lie flat over the abdomen when not in use, a condition called neopterous. This modification serves to protect the wings when not in use and aids in the cooption of the wings for purposes other than flight. The first of those orders with such wings are the stoneflies, who, like the mayflies, dragonflies, and damselflies, live in freshwater as naiads during their juvenile stages and are excellent indicators of water quality, perishing quickly with the introduction of pollutants. Their scientific ordinal name, Plecoptera (from the Greek plék, meaning “plait”) refers to the pleating of their broad hind wings—a feature actually shared by several other groups—which are folded when at rest. Males and females communicate by drumming their abdomens on a surface, locating each other via Morse code–like signals that are unique to each species. The adults of the nearly thirty-five hundred species feed little, spending their time on locating a mate and courtship. Many stonefly mothers lay their eggs while flying, dropping eggs en masse as they fly low over the surface of the water, much like a bomber, while others skim the surface of the water and use the action to “wash” the eggs from her abdomen.

  Stonefly naiads generally feed on algae and aquatic plants, although some groups have become omnivorous scavengers or even carnivores, and nearly all can be found pressed against the undersurface of stones in the water, hence the common name, where they avoid predators. The long-bodied naiads are active swimmers and have a series of unique muscles in the abdomen that allow them to undulate the body side to side while swimming, much like a fish. They are the only such aquatic insects able to produce such movements.

  Diverse winged insects: three castes of the termite Reticulitermes lucifugus (worker at upper left, winged queen at top center, soldier at upper right); the webspinner Embia mauritanica between the worker and solider termites; the stoneflies Brachyptera risi and Perla marginata at middle; and the book louse, Psocus bipunctatus, at bottom. From Cuvier, Le règne animal distribué d’après son organisation.

  EMBIODEA AND ZORAPTERA

  There are two likely related orders of insects that include minute, rarely seen species living in small, gregarious colonies. The first order comprises the webspinners. While the name webspinner might bring to mind spiders and orb webs hanging near porch lights, here it refers to the taxonomic order Embiodea, a name that signifies the insects’ liveliness: from the Greek embios, “lively,” and eîdos, “appearance” or “form.” These tiny insects live in silken galleries spread out over tree trunks or rocks, the silk spun from large glands in their forelegs. The webspinners, which are typically between 7 to 20 millimeters in size, live in colonies of usually fewer than thirty individuals all residing within the silken confines of their galleries. Females watch over their eggs within the gallery and take care of the young nymphs. Typically, females may shed their wings after establishing a new gallery, but when the wings are present they are unusual among flying insects. The veins are diaphanous and form sinuses between the membranes that make up the wing, but they are flexible and collapse easily, a necessary detail so that they do not become entangled when moving backward through the silken tunnels. Even though such a flimsy structure would seem ineffective for flight, webspinners are quite lively flyers when in the air. This is achieved by pumping blood into the sinuses of the wing, the pressure stiffening it to support flight.

  Similarly gregarious, although living under bark of rotting logs rather than nestled amid silk, are the tiny Zoraptera. These insects, which are usually less than 3 millimeters in length, were discovered only about a century ago, in 1913, and are so infrequently met with that they lack a common name—although some have tried to promote the idea of calling them angel insects. They usually look like chestnut-brown termites but are wholly unrelated. The logs in which they live must be soft, such that the bark easily crumbles in one’s hand. Zoraptera live in small groups of usually less than one hundred individuals. Within a colony, females lay a few eggs at a time, watching over and constantly grooming them to remove pathogens like bacteria or fungi.

  Perhaps what most distinguishes Zoraptera are that they come in two different forms, which occur during different phases of a colony’s life. Most of the time they are blind and wingless, feeding on fungi, nematodes, and sometimes mites. The wingless forms were the first Zoraptera discovered by the Italian entomologist Filippo Silvestri (1873–1949), whose university office looked out toward nearby Mount Vesuvius. Believing them to be utterly incapable of flight, he gave them a name that means “purely without wings” (in Greek, zoros, “pure,” with the prefix a-, called the alpha privative and expressing negation). It was not long, however, before the error of this name was revealed. These insects do have wings, but only when it is time to disperse. As the logs in which they live decay away to nothing or the colony becomes overcrowded, some of the eggs laid produce individuals that have large eyes and paddle-shaped wings with faint marks where once were veins. Fully capable of flight, these individuals disperse to find new logs, and upon establishing a new home, resume laying eggs that hatch into the flightless and sightless.

  NOTOPTERA

  Another recently discovered group, first classified as an order in 1915, are the wingless ice crawlers of the Northern Hemisphere and the heel walkers, or rock crawlers, of sub-Saharan Africa, both relicts of animals that were once widespread and previously winged, and that today are represented by about fifty species. Together they are known as the Notoptera, a name referring to the back of their thorax (n ton, Greek for “back”); the man who named them, Guy C. Crampton (1881–1951), originally believed that the absence of wings was due to their having been superseded by a small extension of the back. The ice crawler—which looks a bit like a cross between a cricket and a wingless roach—darts about snow packs scavenging or capturing small arthropods that are moving sluggishly due to the cold. Although they avoid warmer temperatures, ice crawlers are not impervious to the cold and will die if the temperature falls much below freezing. By contrast, their southern sisters in Africa, the heel walkers, thrive in warm, dry climates, where they are nocturnal in rocky or grassy habitats. Heel walkers hold the tips of their feet up as they move, hence their unique name. Resembling a squat mantis combined with a stick insect, the heel walkers were only described in 2000, although specimens had sat in research collections for nearly one hundred years before that.

  DERMAPTERA

  A more familiar group of flyers, the earwigs have been plagued with a bad reputation for centuries and still evoke fear and revulsion. Their common name originates from the Old English arwicga (“ear insect”— are, “ear,” and wicga, “insect”) inspired by the myth that they burrow through the human ear into the brain to lay their eggs, bringing on pain and insanity. In reality, these insects do nothing of the sort, and while it is true they prefer to live in dark, warm, and often damp crevices, they are typically found under bark or stones, or amid the litter of leaves on a forest floor. On an extremely rare occasion, an earwig has been known to crawl within the opening of a human ear or nostril, but only for warmth during a cold night, and such exceedingly rare occurrences can just as likely occur with a beetle or other insect. Quite contrary to their nasty reputation, some earwigs are used to control the population of agricultural pests, particularly on kiwifruit and some citrus crops. The approximately two thousand species are principally found in tropical and warm temperate regions where they are largely nocturnal omnivores, although some may be strictly herbivorous or even carnivorous.

  Perhaps what makes earwigs most recognizable are their characteristic forceps at the tip of the abdomen, used for capturing prey, holding their mates, and folding their distinctive fanlike hind wings. Their scientific ordinal name, Dermaptera, however, refers to the form of their reduced forewings—small, hardened plates that often have a texture resembling leather—dérma means “hide,” as in a leathery animal pelt. These forewing
plates do not function for flight and instead are covers for the hind wings when not in use, although some earwigs are entirely wingless. Earwigs are doting mothers, and while they do not live in social colonies with other individuals, they exhibit great care for their own eggs and young nymphs. In fact, we know from the fossil record that this trait of extensive brood care is ancient among earwigs, with clusters of nymphs from the ancient roosts of extinct species dating back over one hundred million years. After a couple of molts, the nymphs are ready to fend for themselves and by this time must do so, as otherwise the once-caring mother may suddenly turn on them!

  Two groups of earwigs have departed from this general pattern of life, each becoming parasitic on mammals, but as the result of quite independent evolutionary events. While the groups of parasitic earwigs specialize on different hosts, both became wingless, lost their forceps, and became blind with only vestigial eyes. They both give birth to live young rather than lay eggs. Each is rather flattened and suited for moving about undetected amid their host’s fur. They often do not live entirely on the host and will retreat to the mammal’s roost when not feeding. Those occurring in Africa live in the nests of rats native to the region, where they scrape dead skin and fungus from the host, and constitute the family Hemimeridae. The others, forming the family Arixeniidae, are found in Southeast Asia where they function similarly as parasites on bats. Like their many nonparasitic relatives they most certainly do not burrow into ears, nor do they drive rats and bats insane.

  Despite the myth that earwigs burrow into the ear canal and induce madness, species such as the common European earwig (Forficula auricularia) are quite benign and the females are actually doting mothers to their young. From John Curtis, British Entomology (1823–1840).

  An original plate pattern (used by a colorist to hand-paint the plates in each book) from E. F. Staveley’s British Insects (1871). It depicts varied winged insects: at top, the common European earwig (Forficula auricularia); at middle (left to right), the house cricket (Acheta domesticus), katydid (Tettigonia viridissima), and large marsh grasshopper (Stethophyma grossum); at bottom (left to right), the dusky roach (Ectobius lapponicus) and a minute thrips (perhaps a species of Phlaeothrips).

  ORTHOPTERA AND PHASMATODEA

  The grasshoppers, crickets, and katydids are the opera stars of the Insecta. Along with their many relatives, including locusts, the twenty thousand known species comprise the order Orthoptera (orthós, Greek for “straight” or “proper,” refers to their elongate, generally straight forewings). Although famed for their sounds, the calls of Orthoptera are not vocalizations at all; instead they are the product of the wings rubbing together or the legs rubbing against the wings. Of course, if one is singing, then there must be an audience and a means by which to hear. The “ears” of the insects, called tympana, are formed of small chambers outwardly bordered by a thin membrane, acting much like our own eardrums. However, the tympana are not positioned on the sides of the head but instead are on the forelegs. The fattened hind legs, used to give Orthoptera their forceful leaps, are another distinction. Nearly all species are insatiable herbivores and familiar sights among the leaves of our gardens and crops. Most are solitary, although some can become gregarious, and at their most nightmarish can darken the skies with swarms of locusts—the very stuff of biblical plagues. Not all are easily seen, and many of us have been up at night trying to pinpoint a pesky cricket whose nightly song is preventing slumber. But the real way in which species avoid detection is through coloration that often resembles their environment, such as many of the katydids whose wings are so leaflike in appearance as to make them virtually invisible amid foliage.

  The real champions of disguise, however, are the stick and leaf insects, together belonging to the order Phasmatodea, so named for their ability to disappear from view. Their name literally means “form of a phantom”—in Greek, phásma, “phantom,” and eîdos, “appearance” or “form”—and for this reason they are sometimes called ghost insects. All stick and leaf insects are herbivores and live out their lives on foliage, in shrubs, or on the trunks of those trees that they mimic. There are over three thousand species, and most of these are active at night, moving relatively little during the day and blending into their surroundings. Many stick insects are wingless, as they have little need of flight. What is remarkable is that wings have been lost and regained among stick insects many times throughout their evolution, disappearing and reappearing like someone repeatedly turning on and off a light. This is achieved by a simple switching on and off of the genetic mechanism signaling for the development of wings, and while wingless stick insects may not exhibit wings, they fully retain the genetic code to produce wings.

  Sundry grasshoppers (order Orthoptera) and two earwigs (order Dermaptera). From Carl Eduard Adolph Gerstaecker, Baron Carl Claus von der Decken’s Reisen in Ost-Afrika in den Jahren 1859 bis 1865 (1873).

  Gaudy katydids—Parasanaa donovani, Sanaa imperialis, Scambophyllum sanguinolentum, and Calopsyra octomaculata—leap lively in Westwood’s Cabinet of Oriental Entomology.

  There are over three thousand species of stick and leaf insects worldwide, and while the wings of many have become vestigial or been completely lost, there are many who retain the ability to fly. They tightly fold their wings along their elongate bodies when not in use. From Westwood, Cabinet of Oriental Entomology.

  The massive Malayan jungle nymph (Heteropteryx dilatata) is among the heaviest of Phasmatodea at up to 2.3 ounces (65.2 grams), and also holds the record for the largest eggs among insects, at about one-half inch (12.7 millimeters) in length. This illustration appeared in John Parkinson’s account of the species in Transactions of the Linnean Society (1798).

  Stick insects include the world’s longest living insect, Phryganistria chinensis from southern China, whose slender body extends to over 24.5 inches (62.2 centimeters)—just over 2 feet (.6 meters)! Some species are hefty, and the broader and more leaflike females of Heteropteryx dilatata from Malaysia are beasts, weighing in at about 2.3 ounces (65.2 grams), or nearly four times the weight of your average hamster. One of the scarcest insects on Earth is also a stick insect. The Lord Howe Island stick insect, Dryococelus australis, is a large, spiny, and wingless species that was eradicated by rats arriving on a cargo ship that ran aground on the eponymous island in the Tasman Sea in 1918. Within two years the stick insects were gone; that is until a tiny population of no more than twenty-four individuals was found living on an isolated rocky peak no more than 980 feet (299 meters) wide and towering out of the Pacific, 12 miles (19 kilometers) south of Lord Howe Island.

  The remarkable mimics of the order Phasmatodea include species evolved to resemble leaves, such as the Southeast Asian walking-leaf (Phyllium siccifolium), top, as well as to camouflage themselves as twigs or sticks, like the European stick insect (Bacillus rossius, bottom). From Cuvier, Le règne animal distribué d’après son organisation.

  In many species of Phasmatodea the males are particularly rare and difficult to find, but this has nothing to do with their mimicry. Instead, the scarcity of males results from rampant parthenogenesis, whereby females do not require a mate to produce fertile eggs, effectively cloning themselves generation after generation. One might jokingly say that the males made themselves so well hidden that they became inconsequential!

  MANTODEA, BLATTARIA, AND ISOPTERA

  Three closely related groups are the mantises, roaches, and termites, or the orders Mantodea, Blattaria, and Isoptera. In fact, the last of these, the termites, are essentially specialized, social roaches.

  The praying mantises, who perhaps should more properly be called “preying” mantises, encompass about twenty-five hundred species of truly spectacular predators. They have large eyes situated on a highly mobile head that is thrust forward on an extended neck, giving them a wide range of view. Not surprisingly, they have excellent visual perception and will readily interact with you by following a finger. Mantises have large, grasping forelegs, usual
ly beset with spines, for grasping their prey. When the forelegs are folded, this gives mantises their characteristic “praying” appearance, to which their name, Mantodea, refers (the Greek mantis means “soothsayer”). Individuals are quick enough to snag a fly from the air, and if you’ve ever attempted to grab a fly in flight, then you know how difficult this can be. The largest of mantises can be up to almost 8 inches (20.3 centimeters) in length, and some giant species can take down frogs, small lizards, or fledgling birds. As predators, mantises often have coloration that allows them to lurk amid foliage undetected. At their most extreme, some mantises mimic flowers, assuming bizarre shapes in order to blend into their floral surroundings. Mantises are infamous for their sex lives, in which females typically consume the males after—or even during—mating. Mantises lay groups of eggs in hardened, protective cases, called oothecae, a trait shared with the roaches.

  While mantises and roaches are seemingly quite different, such as these Central American species of both, they are actually close relatives; both groups lay eggs in hardened cases called oothecae. From Biologia Centrali-Americana. Insecta. Orthoptera. (1893–1909).

  Predatory mantises (order Mantodea), with their raptorial forelegs, such as these lustrous species from Madagascar, have long been a favorite among naturalists. From Henri de Saussure, Histoire physique, naturelle et politique de Madagascar, Orthoptères (1895).