Social insects represented by workers and a winged male of various species of Malagasy ants (family Formicidae) from A. Forel’s 1891 contribution to the Histoire physique, naturelle et politique de Madagascar.
The arboreal nest of the Malagasy acrobat ant (Crematogaster ranavalonae), built up of twigs and leaves and bound together in a carton composed of chewed plant material mixed with soil, which hardens into an impenetrable wall. From A. Forel, Histoire physique, naturelle et politique de Madagascar.
An exquisitely rendered lithograph of a nest of the Bornean termite Dicuspiditermes nemorosus, a species first discovered by George Haviland, who made a detailed account of their elaborate nests. From “Observations on Termites…,” The Journal of the Linnean Society of London. Zoology. 1898.
While some macrotermitine nests really are mound-shaped, others extend upward like blades, broad but thin. The blade-shaped nests are built such that their broad surface is oriented to the sun, catching the rays of first light to help warm the colony after a cold night. Looking across an African savannah, one can find the landscape studded with dozens of such colonies. The heights attained by these nests are impressive, and are large enough that elephants will use older mounds to scratch themselves. To put this achievement into perspective, consider the current tallest building in the world, the Burj Khalifa of Dubai. This impressive tower extends a staggering 2,722 feet (829.7 meters) into the sky, a little over one-half of a mile, with 163 individual stories above ground topped by a massive spire. The average height of a Western male is generally 5 feet 9 inches (1.75 meters), meaning that at our current best, humans have built a structure approximately 473 times our size. This is trivial compared to what insects can achieve. In the largest termite species, Africa’s Macrotermes bellicosus, the average worker—the caste that labors to build their colossal structures—is 0.14 inches (3.6 millimeters) in length, and some build nests that extend 27 feet (8.2 meters) into the air. The termite mound is therefore about 2,286 times the size of the workers. This is a conservative minimum value, as many workers are even smaller—and their towers do not include spires with unusable space. Were we to build today something of equivalent proportion, the building would have to be at least 13,147 feet high, or 2.49 miles, and consist of no less than 1,314 stories!
SQUATTERS AND FARMERS
The nests of social insects house entire industries of other insects, all eager to benefit from the protective enclosure and concentration of resources residing therein. These insect squatters, called inquilines, include mites, true bugs, and a spectacularly diverse fauna of specialized rove beetles. Inquilines use all kinds of means to gain access to nests and remain undetected once inside. Some, like termite bugs, are flat with textured backs meant to mimic the walls of termite tunnels, thereby camouflaging themselves by pressing tightly against the tunnel walls. Rove beetles not only at times mimic their hosts—such as those who resemble ants—but are also excellent chemists, secreting scents identical to those of the ants and termites with whom they live. They will even copy the behaviors of their hosts, all so they might move about the colony without raising alarm.
The remarkable architectural achievements of the mound-building termites of western Africa Macrotermes bellicosus were initially made known to European scholars though an eloquent letter from English naturalist Henry Smeathman to the famed explorer Sir Joseph Banks, who published the missive Some Account of the Termites Which Are Found in Africa and Other Hot Climates in 1781.
While we like to think ourselves clever for having developed crop species and domesticated livestock, social insects evolved agriculture and animal husbandry eons before we did so in the Neolithic. Ants, termites, and beetles have each evolved agricultural systems, cultivating crops of fungi from which they derive their nourishment. Unlike us, for millions of years these insects have practiced sustainable agriculture, while we struggle to adopt such methods in the cultivation of our crops. There are, however, some forms of insect agriculture that do cause damage to the environs while they go about their cultivation.
Ambrosia beetles live in galleries dug through living trees, and they inoculate the walls of their tunnels with a fungus that infests the surrounding wood. As the fungus grows, the beetles feed upon it. Newly dispersing beetles then take samplings of the fungi with them when they found new galleries. The infamous mountain pine beetle (Dendroctonus ponderosae)presently devastating forests in Canada and the western United States, is an ambrosia beetle that introduces a blue stain fungus, Grosmannia clavigera, to pine trees. The fungus not only serves as a source of food for the beetle but also inhibits the natural defenses of the trees, such that they do not exude resin. The burrowing beetle larvae ultimately circumnavigate the tree, cutting off its internal water flow, and together the beetles and fungi leave their host dead.
In a manner more similar to human farmers, fungus-growing termites and ants cultivate actual gardens, grown within specialized chambers deep within their nests. While fungus-growing ants are restricted to the New World, farming termites are only found in the Old World, so the two groups do not ever overlap. Fungus-growing termites usually cultivate their crops on beds of dead plant tissue or animal feces. The fungus produces nodules that are then collected and consumed by the termites. New queens who found new colonies must locate a starting sample of the fungus in the surrounding environment. This is easily done by collecting spores that are emitted from mushrooms sprouting from the sides of older termite mounds.
LIFE AND DEATH IN ARABIA FELIX
While Carl Linnaeus’s name is synonymous with biological classification, his contributions went well beyond his writings. He was also a gifted professor, giving popular lectures at Uppsala University and organizing botanical excursions that attracted many. Some of Linnaeus’s most promising students undertook voyages of exploration in order to bring botanical and other biological specimens back to Uppsala, so that a fuller picture of God’s grand design might be understood. These adventurous students became known as Linnaeus’s “apostles,” and as journeys to exotic locales in the eighteenth century were often fraught with peril, it is perhaps unsurprising that not all survived their ordeals. One of these intrepid young men was Peter Forsskål (1732–1763), a free-thinking Swede who had earlier written the tract Tankar om borgerliga friheten (Thoughts on Civil Liberty) (1759), which included, among other things, heretical notions such as freedom of speech; it was a virtual blueprint of the United States’ Bill of Rights, which would appear several decades later.
In 1760, Forsskål was assigned to join an expedition, launched by the Danish king Frederick V (r. 1746–1766), to Arabia Felix, the southwestern portion of the Arabian Peninsula that today encompasses southern Saudi Arabia and Yemen. Arabia Felix included the fabled kingdom of Sheba, and one goal of the expedition was to bring back ancient copies of biblical scriptures that were presumed to be there for the taking. Aside from Forsskål, the group consisted of the Danish philologist Frederik C. von Haven (1728–1763), German artist Georg W. Bauernfeind (1728–1763), Danish physician Christian C. Kramer (1732–1763), Lars Berggren as man-servant, and Carsten Niebuhr (1733–1815), a German of humble background relative to his compatriots but who was a skilled mathematician and cartographer.
A map of Arabia Felix by Carsten Niebuhr, the frontispiece to Peter Forsskål’s posthumously published work Flora Aegyptiaco-Arabica (1775). Forsskål, the devoted student of Linnaeus, did not survive the ordeals of his expedition, and it was left to Carsten Niebuhr to publish his friend’s copious manuscript notes in several volumes.
The team left from Copenhagen in January 1761, venturing first to Constantinople and Alexandria, then Cairo, and ultimately arriving in Arabia in 1762. The greatest danger they had endured en route was one another—tensions were high among the multinational crewmembers, and at times the atmosphere even became rife with fears of suspected plots of subterfuge. The danger from marauding tribes and deceitful scoundrels as well as the hardship of travel in a hot and arid land eventual
ly melded most of them together as dear friends. By Cairo, all but von Haven had adopted Arab dress and methods of living, knowing that becoming one with their environment and building compassionate friendships with their hosts was critical to the survival of all.
Throughout their journey, Forsskål made collections of plants and animals, preparing copious notes to be shared with Linnaeus upon his return. They were also to serve as the foundation for a grand treatment of the Arabian and Egyptian biotas. Unfortunately, the expedition was plagued by many misfortunes. The group finally reached Yemen on December 29, 1762, but sadly, five months later, von Haven succumbed to malaria. He was followed in death by the hopeful Forsskål in July 1763, who also had contracted the disease. Niebuhr and the others buried him outside of a small montane town near Sana’a where he had passed. The remaining explorers made their way back to the coast, each falling ill. They eventually found passage on an English vessel bound for India, but while traversing the Indian Ocean, both Bauernfeind and Berggren perished of the disease, their bodies committed to the depths. In Bombay, Kramer died, and so by February 1764, Niebuhr was the only one who remained.
The title page to Peter Forsskål’s posthumously published work on the animals discovered during his travels through Egypt and Arabia, Descriptiones Animalium, Avium, Amphibiorum, Piscium, Insectorum, Vermium (1775).
Niebuhr slowly made his way back to Europe, traveling by ship to Oman and then to Persia, along the way visiting the ruins of ancient Persepolis—one of the first Europeans to see the city and, in fact, the first to prepare detailed accounts of its monuments and cuneiform writing. By way of today’s Iraq, Syria, and Turkey, Niebuhr finally reached Constantinople once again in January 1767, and by November of that year he arrived safely in Copenhagen, where the whole expedition had begun six years earlier. He wrote an account of the expedition, and so as to not see the labors of his dear friend Forsskål perish, he published what remained of Forsskål’s monographs on the flora and fauna of the Red Sea environs of Egypt and Arabia.
The title page to the atlas volume of Descriptiones, containing the various images of the plants and animals discovered during Forsskål’s exploration of Egypt and Arabia.
Forsskål discussed twenty-five insect species, including one he called Gryllus gregarius, and that we today know as the voracious desert locust (Schistocerca gregaria), the scourge of biblical plagues. He also described and depicted a soldier and worker of the subterranean termite Reticulitermes lucifugus (called Termes arda by Forsskål) as well as one of their constructed tunnels; the species is notorious for its damage to human structures throughout the Middle East and Europe. These are among the earliest images of the castes of termites. Forsskål’s account also included one mosquito, Culex molestus (today known as Culex pipiens form molestus), so called because of the incessant botheration it makes of itself. While it is not a species that transmits malaria, it is chilling to think of how its brethren helped bring to ruin the journey of Linnaeus’s pupil and his companions.
Forsskål’s work included the first figures of the social castes of termites, showing workers and soldiers of the subterranean termite Reticulitermes lucifugus, as well as portions of their nest constructions. This illustration also included other arthropods he discovered, such as the spider Argiope sector and the thread-winged lacewing Halter halterata.
The most adept insect farmers, however, are ants. Fungus-growing ants have perfected gardening and have been at this activity for at least the last fifty million years. Unlike the termites, ants harvest clippings of leaves upon which to grow their fungus, and queens founding new colonies carry with them a culture of the fungi used to develop a new garden. Like human farmers, the insects face challenges with maintaining a suitable climate and avoiding crop pests, the latter being other fungi or bacteria that may devastate their gardens. To avoid introducing any unexpected “pests” into their gardens, the ants groom themselves and clean their gardens constantly, and some cultivate specific bacteria and yeasts that act as antibiotics, functioning like “weed killers,” to keep the gardens healthy.
Other groups of ants have also evolved to tend plant-sucking aphids or treehoppers, collecting “honeydew” from them. Aphids suck sugary fluids from their plant hosts, consuming massive volumes from the plant in order to gain sufficient nutrition. This heavy flow through their bodies produces considerable fluid wastes; they excrete droplets of this honeydew, which is rich in sugars, much like nectar, and it is therefore desirable to the ants. The ants have evolved to become ranchers, looking over a herd of aphids like tiny cattle. Some ants will even “milk” the aphids like dairy cows, stimulating the aphid to secrete drops of honeydew on command through a stroke of the ant’s antennae. The aphids are protected by the ants, and the ants feed on the honeydew, representing an ideal mutualism. Like human ranchers, should a “field” become used up, the ants will carry their herd to a new location where “grazing” is more suitable. The ants even collect the aphids’ eggs and bring them within their nests during winter months, protecting them from the harsh cold. They then carry the aphid nymphs out to feed once spring arrives.
A diversity of ants (family Formicidae)—queen, workers, and males. Ants are among the most familiar of social insects, living in highly integrated societies throughout the world. From Georges Cuvier, Le règne animal distribué d’après son organisation (1836–1849).
Detail of a dwarf honey bee (Apis florea) comb, with (left to right) drone, queen, and worker above and a sole worker on the comb itself. At bottom right, a worker of the giant honey bee (Apis dorsata). From Charles Horne and Frederick Smith, “Notes on the Habits of Some Hymenopterous Insects…,” Transactions of the Zoological Society of London, 1870.
“The limits of my language mean the limits of my world.”
—Ludwig Wittgenstein
Tractatus Logico-Philosophicus, 1922
“Bzzz.”
—Honey bee
The American poet A. R. Ammons (1926–2001) wrote, “Two things are dead giveaways in nature: one is moving, making a motion, and the other is making a sound. Because these two are so risky, wild nature is mostly still and quiet.” But life—and “wild nature”—are about risk. Whether we notice it or not, all around us species constantly take risks by both moving and making sounds. A crescendo of communication surrounds us, and while it is true that there are times when we might be stunned by the “deafening” silence of a forest like Ammons describes, there are many occasions on which we may feel deluged by the noise of abundant life—from the songs of birds to the symphonies of crickets. Nature is often neither still nor quiet. Yet, our noisy human world has left too many of us tone-deaf, so much so that when we find ourselves in the great outdoors we may fail to take notice of the variety of calls that envelope us. Each sound and each movement that alerts a predator is indeed risky, but wild nature must risk all in order to truly thrive. Only by doing so can animals—including insects—complete their lives: find food, locate and choose a mate, and keep their species thriving.
Our lives revolve around communication. We talk to our loved ones, to our coworkers, sometimes to ourselves, and even to our pets. Right now you are reading a silent form of communication involving an agreed-upon set of abstract scrawls to represent the sounds of words that would otherwise be spoken. Our other senses are also involved in communication: smells tell us of delicious meals, warn us of dangers, and fill us with memories; touch can similarly provide us with a flood of information. Our natural and cultural habit of gathering and sharing information is one of the defining traits of our civilizations and species.
Every insect species communicates in one form or another, and any nice summer’s evening attests to this profusion, with its background chorus of chirping crickets and roaring cicadas, and the gentle flashes of fireflies. The concert of sights and sounds goes well beyond these familiar signals—beetles stridulate, roaches hiss, stoneflies drum, moths send ultrasonic bursts, treehoppers buzz twigs, and any number of others d
ance. In fact, insects communicate via every modality imaginable—including some that we were scarcely aware of until recent decades. The most basic signal-receiver systems are those between male and female, parent and offspring, and prey and predator. Males and females must find each other within a varied and changing environment, often filled with hazards. Females signal to their broods when danger is near, and countless species warn potential attackers of their noxiousness through bright and distinctive palettes of color. Whether we “hear” it or not, there is a virtual cacophony of communication underway at all times in the insect world.
Crickets, grasshoppers, and katydids are among the most familiar “singing” insects. At top, the Asian sandy cricket (Schizodactylus monstrosus); in the center, the ant-loving cricket (Myrmecophilus acervorum), which lives in ants’ nests and more superficially resembles a roach nymph; and at bottom, the great green bush katydid (Tettigonia viridissima). From Georges Cuvier, Le règne animal distribué d’après son organisation (1836–1849).
The migratory locust (Locusta migratoria), the most widespread of locusts, has the potential to form massive swarms with tens of millions of individuals per square mile. From John Curtis, British Entomology (1823–1840).
The large Asian sandy cricket (Schizodactylus monstrosus, top) has characteristically curled wing tips and flattened lobes that extend from the legs. They are a delicacy to some native peoples. The tobacco cricket (Brachytrupes membranaceus, below), native to Africa, feeds on young tobacco plants. From Dru Drury, Illustrations of Exotic Entomology (1837).
Innumerable Insects Page 14