A nest of the Bornean termite Dicuspiditermes nemorosus (see also page 136). From George D. Haviland, “Observations on Termites…,” The Journal of the Linnean Society of London. Zoology, 1898.
“No man is an island.”
—John Donne
Devotions upon Emergent Occasions, Meditation XVII, 1624
Humans are social animals—at least most of us are—and it is only natural that we should have a particular affinity for those other species that exhibit similar societal instincts. We see in such animals ourselves and parallels of our own evolution. Social interactions come in a wide gradation of forms, from degrees of parental investment to large communities teeming with thousands, if not millions, of individuals. Outside of humans, almost all instances of truly complex animal societies are found among arthropods, and the majority of these are spread across the insects.
A society, of course, consists of individuals working together. The simplest social expression may be that of extended care on the part of a mother tending her brood. The insect world teems with protective mothers, ranging from earwigs to leaf beetles, and many of their behaviors are not all that different from those of birds tending their eggs or feeding their chicks. Gregarious associations, such as large aggregations of springtails or even the coordinated swarms of locusts, also represent a simple form of social behavior. In some species, insects of the same generation will come together within a common structure, such as a branching burrow underground or a thicket of spun silk in trees. Within these collective nests, the community garners the advantages of group protection, but otherwise each mother raises her own offspring independently of the others. These types of communal societies are found among tent caterpillars, some bees and wasps, and beetles.
The ultimate expression of sociality is one in which overlapping generations of females come together within a shared nest and collaborate in the care of a brood, even though the offspring come from only one or a few of the total females involved. This form of social behavior is called eusocial, a term coined in 1966 by American bee biologist Suzanne Batra (b. 1937) that literally means “truly social” (the prefix eu means “true” and is derived from the ancient Greek for “well” or “good”). Within a eusocial society some females forego their own reproduction in order to help rear the offspring of another related female or subset of females. These nonreproducing females are known as workers, while those that lay eggs are the queens, and these are distinct castes within the society. In the most primitive eusocial societies, the workers are capable of laying their own eggs but do not do so, opting not to mate and instead work solely in aid of the queen, who is either a sister or their mother. Should the queen be injured or die, any one of the workers might then succeed her as a new queen. The caste distinction is therefore one of behavior, and there is a flexibility to the societal structure. Bumble bee societies are based on this model.
A diversity of Hymenoptera (ants, bees, and wasps) and their nests—from subterranean ants (family Formicidae) in their gallery; to ground-nesting, solitary bees (family Andrenidae) and the cuckoos that prey upon them (family Apidae); to the papered colonies of yellowjackets and the earthen pots of potter wasps (family Vespidae). From Jules Rothschild, ed., Musée entomologique illustré: histoire naturelle iconographique des insectes (1876).
The nest of the buff-tailed bumble bee (Bombus terrestris) consists of a series of simple pots loosely clustered together, some of which are used to store food, while others are the chambers in which larvae develop. From William Jardine, ed., Bees. Comprehending the Uses and Economical Management of the Honey-Bee of Britain and Other Countries . . . (ca. 1846).
Some eusocial societies, however, have caste systems that are more rigidly set in place, with there being considerable anatomical differences between the sterile workers and the queen caste. In this these societies it is not possible for a worker to replace the latter. In fact, some of the most ubiquitous and ecologically dominant of all insects are such highly eusocial species, specifically the triumvirate of termites, ants, and certain species of bees, including honey bees. While all ants and termites are highly eusocial, among bees, social behavior is the exception rather than the rule. Most of the twenty thousand species of bees are solitary, and those that form characteristic eusocial societies represent perhaps no more than 5 percent of this diversity. The eusocial societies of these three insect lineages form a virtual hegemony over our world. They are, however, not the only eusocial groups; there are some eusocial aphids and thrips, and there is even a primitive eusocial species of ambrosia beetle that lives in galleries (tunnels) in the heartwood of eucalyptus trees in southeastern Australia. Outside of the insects, eusociality is rare. It is found in some spiders and snapping shrimps, but in only two other animals; the naked mole rat of the Horn of Africa and southern Africa’s Damara mole rat are the only eusocial vertebrates. Some argue that subsets of human society meet the criteria for eusocial behavior, so we might include ourselves in this distinguished company.
For most of human history, the majority of people lived under the rule of a leader who was typically male—a chieftain, a king, or an emperor—one whose will, whether it was just, wise, or even deranged, would determine the fates of all others. Communities of social insects were miniaturized versions of our own civilization in the minds of early naturalists, and it is reasonable that they assumed the toiling laborers of insects were male and that the monarch over these workers must be a king.
In 1586, Spanish apiculturist and author Luis Méndez de Torres first speculated that in bee colonies, the insect king was in fact a queen. Two decades later, the father of modern beekeeping, English vicar Charles Butler (1560–1647) published his seminal work on the honey bee, entitled The Feminine Monarchie (1609) (see pages 163-165). Jan Swammerdam (see pages 82-83) would confirm the female gender of the bee monarch through his microscopic study of apian dissections in the 1670s, demonstrating that the “king” bee had ovaries and therefore must be female. The workers, too, proved to be female, showing that bee societies are dominated and run by females, while males serve only to fertilize the queen. Despite finally giving the queen proper credit for her gender, a prior notion that she never mated still persisted. Swammerdam insisted that the male impregnated the queen by some means of seminal spirit, which he called the aura seminalis, but was incapable of actually copulating. It took the keen observations of the Swiss naturalist François Huber (1750–1831) to put this pernicious rumor to bed in his book Nouvelles observations sur les abeilles (New Observations on Bees) (1792). Huber’s “observations” are particularly remarkable when one considers that he was totally blind. Through careful experiments outlined by Huber and executed for him by his wife, Marie-Aimée Lullin (1751–1822), and his manservent, François Burnens, Huber confirmed that a single queen reigns over the hive, that she lays all of the eggs, and that she most certainly indeed does mate with a male. Huber’s book would become the standard reference on honey bee natural history and beekeeping for a generation, and the glass-paneled observation hive he devised revolutionized apiculture.
The three castes of two highly eusocial wasps: the European hornet (Vespa crabro) and the European paper wasp (Polistes gallicus). From Amédée Louis Michel Lepeletier, comte de Saint Fargeau, Histoire naturelle des insects (1836–1846).
The title page to François Huber’s Nouvelles observations sur les abeilles (1792), whereby he presented an account of his studies on the natural history of the honey bee (Apis mellifera) although he was completely blind.
The two most iconic groups of social insects—ants (family Formicidae) and the European honey bee (Apis mellifera)—and their three castes: queens, sterile female workers, and males (dubbed “drones” among honey bees). From Lepeletier, Histoire naturelle des insects.
The males of eusocial bees are known as drones. Butler correctly realized that the drones were male, but he assumed they mated with the workers. The drones of honey bees are unique among bees in that they die after copulatio
n; the male organ and viscera are ripped off as the drone disengages from the queen. Fortunately the males of other bee species do not suffer such fates. In termite colonies, the reproductive male (there is only one) at least gets the royal title of king, although his only functions in termite society are to act as consort to the queen and release pheromones that help control the other castes in the colony (the queen does this as well). In particular, if a queen dies, then the king emits pheromones that induce the development of replacement queens. Male ants are not so fortunate as to receive a specialized name, perhaps because they do not live long after completing their singular duty to their monarch.
Insectan caste systems are not always binary, consisting of only workers and queens. Some insect societies have a third caste, the soldier caste, which serves the function of protecting the colony. Soldier castes can be found in aphids, thrips, some ants, and termites (see pages 70 and page 74). Soldiers are specialized females that, like the workers, do not reproduce but are anatomically modified for defense. Soldiers have evolved any number of medieval means by which to engage and defeat invaders. At their simplest, many have massive heads and muscles supporting elongate snapping jaws, but others are far more creative. The soldiers of nasute termites (from the subfamily Nasutitermitinae), for example, have heads that are modified into something resembling a squeeze bottle, complete with a forward-directed spout known as a nasus (from the Latin for “nose,” and by extension, a nozzle or spout). Such soldiers spray an aerosol chemical from the spout, either as a repellant or as a glue that ensnares the attackers, which are usually ants. Soldiers are often so highly specialized as to no longer be capable of feeding themselves, relying instead on workers to nourish them.
The first animals to evolve complex societies were the termites, having done so by the late Jurassic, or at least 145 million years ago, a time in which Stegosaurus, Apatosaurus, and Allosaurus roamed over Colorado and Wyoming, pterodactyls soared overhead, and birdlike Archaeopteryx lived in Germany. The societies of ants and bees similarly appeared alongside dinosaurs, out-surviving the latter with the exception of dinosaurs’ feathered descendants, birds. By the time our species appeared approximately 300,000 years ago, the civilizations and cities of termites, ants, and bees had surrounded the globe and survived cataclysms of global intensity. Despite the success and hardiness of these societies, it is sobering to watch how vulnerable they have been to the effects of human-induced climate change and habitat destruction. For example, bumble bees, which are some of our most vital pollinators, are disappearing from many places where they were once abundant.
INSECT ARCHITECTURE
A prerequisite for being social is, of course, a common structure within which to live. However, not all animal architecture is associated with social behavior. In the insect world, the most basic constructions are simple roosts in which a mother rears her offspring. By example, female earwigs will occupy small spaces, ranging from simple burrows in soil to crevices under bark or stones, within which she will tend to her younglings. Solitary wasps and bees dig burrows in which they place collected provisions and lay their eggs, and caddisfly larvae build cases for retreat. Protective cases among solitary insects are familiar—and frustrating—to many homeowners with yards; particularly those of us who have had to pull bags woven from plant materials and silk by bagworms—the caterpillars of moths in the family Psychidae—from our ornamentals. Nonetheless, the constructions of the eusocial insect species are particularly magnificent and have inspired imaginations since antiquity.
The most familiar eusocial construction is the hexagonal comb of a honey bee. There are seven species of honey bees, all of which construct waxen combs of six-sided cells. Within these cells the bees store honey and rear their larvae. For most honey bee species the combs are built within the confines of some cavity, such as a hollow in a tree. The combs hang vertically, and the workers walk about the outer surface, forming a constantly moving curtain of living insects that help to protect and regulate the combs. The bees are remarkably adept at maintaining a constant temperature within the hive, making certain that conditions remain ideal for the developing brood as well as for the preservation of the communities’ stores. Bees can warm the hive by contracting the muscles that move their wings, but while holding their wings in place. This movement generates a great deal of heat as the energy is not released by flight. Bees can also fan their wings to move air and cool the enclosure during particularly hot days.
There is perhaps no architectural feature more recognizable than the waxen hexagonal combs of honey bees (species of the genus Apis). The combs of the domesticated European honey bee (Apis mellifera) can be easily manipulated within wooden frames, making modern-day beekeeping a profitable enterprise. From Lepeletier, Histoire naturelle des insects.
Bumble bees are also eusocial, albeit of the more primitive form, whereby workers are capable of succeeding their queen should the need arise. Bumble bee nests are also found within cavities, and the bees tend to use the abandoned burrows of rodents or birds, nestled amid or under vegetation. The bees construct waxen pots that are grouped into irregular, horizontal clumps. Some pots are used for developing larvae, while others store pollen. Other primitively eusocial bees dig multibranched burrows within the soil, such as the social species of sweat bees. Yet other lineages of primitively eusocial bees, such as allodapine bees, relatives of the more familiar carpenter bees, will excavate burrow within hollow stems.
Like their cousins the bees, stinging wasps such as paper wasps, hornets, and yellow jackets also build elaborate nests, replete with rows of cells. Some nests are dug into cavities within the ground, but the more conspicuous nests dangle from eaves, wrap around branches, or are delicately suspended by slender stalks. While some nests are open, exposing the papery combs—usually with many females covering them and at guard—others are securely encased by papery or hard mud overlays. Wasp colonies can become massive, and one interconnected series of paper wasp combs suspended from the roof of a cave in Brazil was discovered to consist of millions of individual wasps. Those species with smaller colony sizes, or even wasps who are solitary, also build delicate nests, some using leaves as anchors or curling them to form parts of the architecture itself.
Diverse stinging wasps (families Vespidae, Tiphiidae, and Pompilidae) from Madagascar are depicted in Henri de Saussure’s volume Histoire physique, naturelle et politique de Madagascar, Orthoptères (1895). The illustration includes the delicate comb of the social paper wasp (Ropalidia bicincta), which is suspended by a fine petiole (leaf stalk) from the undersurface of leaves.
A woodcut from Ulisse Aldrovandi’s De Animalibus Insectis Libri Septem (1638 [1602]), depicting the paper nest of the common European wasp, or yellowjacket, (Vespula vulgaris).
ANTS AND TERMITES
Like bees, ants and termites are also excellent architects, and in many ways their constructions make honeycombs seem trivial in comparison. While many bee nests are distinctive for their uniform structure, those of ants and termites stand out for their irregularity. Most ant and termite nests are built within different substrates, such as wood or soil. They typically consist of chambers connected by networks of tunnels and have one or more openings to the outside world. Many of these nests are underground and usually go unnoticed by humans, although the galleries that are dug can be intricate.
Thick layers of paper envelopes (made from masticated wood fibers) encapsulate intricate layers of combs within the social nests of the common European wasp. The largest of these nests can house upward of four thousand workers, tending a brood of over fivem thousand larvae during a cycle. From Lepeletier, Histoire naturelle des insects.
The soil excavated by the ants building subterranean nests is brought to the surface and dumped, resulting in small mounds, much like chat piles from human mining activities. These colonies can dig quite deep, with those of some ant species extending to depths of 12 feet (3.66 meters) or more. While it may seem simple to dig tunnels and chambers,
these nests are well planned. At their most complex, they include ventilation mechanisms for circulating air and drainage tunnels for funneling water and wastes away from those chambers serving as nurseries, granaries, or gardens. As with bees hives, the temperatures within can be controlled with great precision. The mounds created by wood ants are particularly familiar sights in forests in North America and Europe. These can be massive, with the largest approaching nearly four hundred thousand workers and forming small mountains exceeding the height of an average man. There are usually small earthen craters at the cores, but otherwise the mounds are built up from twigs or needles from trees. Other ants build their nests in trees, constructing them of twigs, leaves, and other plant materials that they weave together into suitable cities for their colony.
Perhaps the most impressive and easily observed nests are those of macrotermitine termites, a lineage found only in the Old World, whose often colossal nests can define and transform vast landscapes in Africa. At their core, the principal galleries are subterranean or at the surrounding soil level, with a broad cellar from which extends small channels up to and opening on the sides of the mound. These termites cultivate fungi within specialized garden chambers that are situated above the subterranean network of galleries. The mound itself is built of clay moistened by the termites’ saliva, which cements the structure. Cemented is an apt term, as the mounds are extremely sturdy and not easily breached. It often takes a heavy pickax wielded by a particularly strong person in order to make a significant dent. The mounds are porous and have series of chimneys that extend throughout to help regulate airflow as well as control the temperature and humidity within.
Innumerable Insects Page 13