Innumerable Insects

by Michael S. Engel

  A ZEALOT FOR CHANGE

  For millennia it was assumed that larvae, pupae, and adult insects were all unrelated, representing entirely different individuals. It was also believed that many insects were the result of spontaneous generation, sometimes materializing from the putrefied flesh of other animals. Such a notion was anathema to the Dutch physiologist Jan Swammerdam, who would exorcise these ideas from entomology but whose own religious fanaticism eventually led him to cast aside his science.

  Swammerdam was born in Amsterdam in 1637. He matriculated at the University of Leiden in 1661, trained to be a doctor, and graduated in 1667, after a brief leave to work in Paris. While in Paris he befriended the royal librarian of Louis XIV, Melchisédech Thévenot (ca. 1620–1692), who would later send Swammerdam a copy of De Bombyce (1669), a book on the dissection of the silk moth by Italian anatomist Marcello Malpighi (1628–1694). Swammerdam was already fascinated by the minute lives of insects, and his interests were further fueled by Malpighi’s work—much to the consternation of Swammerdam’s father, who wished his son to pursue the priesthood or practice medicine.

  Swammerdam became singularly devoted to natural history. Rearing insects in his home and even nourishing blood-feeding species with his own blood, Swammerdam studied the habits and life cycles of mosquitos, moths, ants, and others, all under microscopic examination and with honed microdissection techniques. He constructed his own instruments and perfected a precision for working with the tiniest of insect organs. Swammerdam is credited with numerous discoveries, not all entomological, from nerve induction of muscular contraction to the lymphatic valves that today bear his name. Above all of these, he is most remembered for dispelling the idea that any insects generated spontaneously, and for demonstrating without question that larva, pupa, and adult are all different stages in the life of a single individual. He was also the one to empirically prove the gender of the queen bee by dissecting her abdomen to reveal ovaries, and he was the one to discover the drone’s male organs. Swammerdam prepared all of his own illustrations, using the latest method of the age, engravings in copper.

  Swammerdam depicted in a print by Johann Peter Berghaus after Rembrandt van Rijn, ca. 1840.

  The title page to a 1685 edition of Swammerdam’s Historia Insectorum Generalis (1669), a work wherein he dispelled ancient misconceptions regarding metamorphosis.

  Swammerdam’s fervor for study was intense, galvanized by his awe at God’s creation. His faith, however, turned to zeal, and in 1673 he walked away from science. By 1675, he had fallen under the spell of the hysterical and persuasive French-Flemish mystic spiritualist Antoinette Bourignon (1616–1680), who led a small group of rogues around Europe, distributing pamphlets of her revelations. Not surprisingly, Swammerdam found his spiritual emptiness was not sated, and in 1677 he rather quickly left the sect, returning to Amsterdam distraught and ill. His father had passed away, and Swammerdam became embattled with his sister over the inheritance. He died in 1680, only in his early forties.

  Before being overtaken by religious zeal, however, Swammerdam published his initial entomological observations in 1669 as Historia Insectorum Generalis (A General History of Insects). His most extensive and fundamental contribution, however, was compiled from loose manuscripts and translated into Latin by Herman Boerhaave (1668–1738). This collection appeared in 1737, fifty-seven years after Swammerdam’s death, as the Biblia Naturae (Nature Bible). The pious Swammerdam’s “bible” of nature truly glorified the multiplicity of creation through empirical science and the fact that one organism could undergo considerable change during its life, much as Swammerdam did himself.

  The various stages of development in an ant (family Formicidae) as worked out by Swammerdam and meticulously figured in copper engravings, from Historia Insectorum Generalis.

  The dobsonflies, along with the related fishflies and alderflies, have aquatic larvae, with the sizable ones familiarly known to fishermen as hellgrammites. These are often large, robust insects, with one monstrous species discovered in 2014 wielding an 8-inch (20-centimeter) wingspan. The derivation of the name Megaloptera is therefore quite apt, as the Greek words mégas and pterón mean “large wing.” A dobsonfly spends most of its life as a larva, living in the water for several years before emerging to build a pupal chamber in the soil and later hatching as a short-lived adult. Male dobsonflies appear ferocious, with long tusklike jaws, but are largely harmless as these ornamentations are used to display for females during courtship and to grasp their mates, but not for hunting. Megaloptera can be found throughout the world.

  Snakeflies, as their name implies, superficially resemble tiny serpents because of their long necks and slender heads, which are often positioned as though they are slightly recoiled. However, the first part of their ordinal name, Raphidioptera, refers to the opposite end of the body. Female snakeflies have long, needle-like ovipositors, and it is this feature that lends them their name—from the Greek raphidos, meaning “needle.” Although distributed globally over sixty-five million years ago, today snakeflies are restricted to temperate forests of the Northern Hemisphere where they are daylight predators, usually feeding on small arthropods. The long ovipositor is used to deposit eggs underneath bark, where many larval snakeflies develop. Immature snakeflies are peculiar among holometabolous insects for two reasons. First, in order to complete their development, the late-stage larva or pupa must undergo a period of near-freezing temperatures, a trait that partly explains their confinement to colder northern localities or higher elevations. Secondly, whereas pupae are generally quiescent, snakefly pupae are active and quite mobile, hunting for small prey just as do the adults.

  Last are the lacewings, which also include antlions and owlflies. Their diaphanous wings are intricately laced by fine veins, much more so than dobsonflies or snakeflies. The beginning of their ordinal name, Neuroptera, derives from the Greek neuron, “nerve,” referencing this very fact. Adult lacewings are usually nocturnal animals that often feed on pollen or nectar, although some consume small arthropods or don’t eat at all—not living long enough as adults to require food. While the adults appear delicate and graceful, the larvae are vicious predators. All larval Neuroptera have modified jaws in which the mandibles and maxillae are united to form vampiric tubes that are used to drain the bodily fluids of their prey. The larvae of green lacewings are effective killers of aphids and often cloak themselves in elaborate camouflage by covering their bodies with pieces of lichen, plant debris, or even the corpses of their victims (see pages 170-171). They are so effective that one of their common names is “aphid wolf,” and they are sometimes employed as biological control agents. Larval antlions burrow backward into loose soil or sand, sitting at the bottom of small pits with their stout jaws spread wide, waiting for ants or other arthropods to stumble to the bottom and meet a rather crushing demise. Perhaps most peculiar of all are the lacewings known as spongillaflies, whose larvae have evolved as predators of freshwater sponges, a form of prey that the predator need not fear will escape.

  Antlions (family Myrmeleontidae, order Neuroptera) and fishflies (family Corydalidae, order Megaloptera) include some of the largest species of their respective orders: top to bottom, Palpares libelluloides, Euptilon ornatum, Chauliodes pectinicornis, and Vella americana. From Dru Drury, Illustrations of Exotic Entomology (1837).

  The wings of lacewings (order Neuroptera) and their relatives are more richly innervated than most other holometabolous insects. Here are shown owlflies, antlions, mantis lacewings, and thread-winged lacewings, as well as a single fishfly (order Megaloptera, upper left). From John O. Westwood, The Cabinet of Oriental Entomology (1848).

  Adults of antlions (family Myrmeleontidae, upper box) and owlflies (family Ascalaphidae, lower right) of the order Neuroptera, and scorpionflies (family Panorpidae, bottom left box) of the order Mecoptera. From Olivier, Encyclopédie méthodique. Histoire naturelle. Insectes.

  COLEOPTERA

  The beetles, order Coleoptera, are so
wholly unlike lacewings, dobsonflies, and snakeflies in general appearance that it is usually a shock to learn that they are all closely related. Beetles are the behemoths of insect diversity, with over 360,000 described species and a steady stream of new species flowing in every year—even from the seemingly over-studied faunae of North America and Europe. There seems to be no end in sight to the growth of coleopteran diversity, and nearly one-fifth of all the known species on our planet are beetles. From this, one can properly appreciate J. B. S. Haldane’s reported reference to God’s seemingly inordinate fondness for Coleoptera.

  The larva of a common European antlion (family Myrmeleontidae) dig characteristic funnel-like pits in soil to trap passing prey. From Rösel von Rosenhof, De natuurlyke historie der insecten.

  Iconic large beetles, clockwise from top left: the harlequin beetle (Acrocinus longimanus); and at right, the sabertooth longhorn beetle (Macrodontia cervicornis). From Rösel von Rosenhof, De natuurlyke historie der insecten.

  Named for the Greek Titan who supported the heavens upon his shoulders, the massive Atlas scarab beetle (Chalcosoma atlas) from Southeast Asia can be over 5 inches (12.7 centimeters) in length. The males use their prominent horns in jousting matches between competitors seeking mates. From Edward Donovan, Natural History of the Insects of India (1838).

  In Greek, coleos means “sheath,” which refers to the hardened and protective covering on the body of the beetle. This characteristic “shell” is actually composed of the front pair of wings, which are specialized forewings called elytra. The hind wings alone are used for flight, and when not in use, these broad wings are folded in a characteristic manner, tucked safely under the elytra and on top of the abdomen, with both abdomen and hind wings covered and protected by the hardened forewings.

  The goliath beetle (Goliathus goliatus) of eastern equatorial Africa is one of the larger species in its genus, with lengths up to 4.3 inches (11 centimeters). From Drury, Illustrations of Exotic Entomology.

  A profusion of tropical American longhorn beetles (family Cerambycidae). From Biologia Centrali-Americana. Insecta. Coleoptera. (1880–1911).

  Beetles come in every shape and size, from the aptly named Goliath beetles of Africa, which can grow to over 4 inches (10 centimeters), illustrated on page 87, to Scydosella musawasensis, the nearly invisible featherwing beetle of Nicaragua, which at just over one-hundredth of an inch (.25 millimeters) in length holds the current record as the smallest of all beetles. We give special names to certain groups of beetles—fireflies, ladybugs, June bugs, and weevils are nothing more than particular forms of this wide-reaching lineage. For any mode of life one can envision, there is certainly a beetle that fits the description: parasites, predators, pollinators, fungal feeders, plant pests, aquatic forms, and even species that prefer to muck about in slime and dung. Virtually everywhere you look, a beetle is to be found. The biggest groups are specialized herbivores, having diversified along with flowering plants, although beetles as a whole are much more ancient, with fossil species recognizable as early beetles dating back 280 million years ago. With their never-ending variety, they have been a favorite of collectors for hundreds of years, and many budding entomologists start as beetle aficionados, Darwin among them.

  The hardened forewings (called elytra) of beetles, often marked with patterns and colors—as well as the inordinate numbers of beetle species—have made them popular with amateur and professional entomologists alike. The elytra of large species, such as the Megaloxantha bicolor (at center), can vary from green to blue to red and have even been used to make jewelry. From Félix-Edouard Guérin-Méneville, Iconographie du règne animal de G. Cuvier (1829–1844).

  Seed beetles (subfamily Bruchinae) are a diverse group among the leaf beetles (family Chrysomelidae). The larvae chew their way into the seeds of various plants; these granivores can be critical pests of crops. From Biologia Centrali-Americana. Insecta. Coleoptera.

  STREPSIPTERA

  The twisted-wings (yes, that is a name), order Strepsiptera, are a group of approximately six hundred species that are exclusively parasitic, and they perhaps hold the distinction of being the most wholly bizarre of all insects. So peculiar are the twisted-wings that identifying their nearest relatives has boggled the minds of entomologists, although it appears as though they are likely relatives of the beetles. In appearance and biology, twisted-wings are unforgettable animals, and it is only their minute proportions and scarcity that prevent them from being more properly scrutinized. Adult males are certainly distinctive, with large, bulbous eyes that resemble blackberries. The forewings are reduced to small, slender stalks that do not function for flight, but rather appear to provide sensory input that aids in orientation. Conversely, the hind wings, which alone power twisted-wing flight, are broad and scarcely retain any of the veins that usually traverse the surface of insect wings. Their name is derived from these flimsy wings, as in Greek, streptós means “twisted.” The male antennae are greatly branched, and the mandibles are vestigial, assuming sensory rather than gustatory roles.

  The enigmatic twisted-wing parasites (order Strepsiptera) have fully winged males while females, who never leave their host, are scarcely recognizable as insects. Clockwise from upper left: Xenos vesparum, Stylops dalii, Elenchus tenuicornis, and Halictophagus curtisii. From Cuvier, Le règne animal…

  The female twisted-wing is another matter entirely. In almost all twisted-wings, the adult females are neotenic, a term referring to the fact that although they are adults, in outward appearance they remain as if larvae. Thus, nearly all females lack eyes, antennae, wings, legs, and even some seemingly necessary organs, such as a rectum. As a parasite, the female lives within the body of her host, such as a bee or a cricket, and does not emerge except to extrude a small portion of her simplified head through membranous joints in her host’s exoskeleton, this being her only connection with the outside world. In another bizarre “twist,” an exposed opening on her head serves as both the site with which the adult male will mate, and the canal through which she will later give birth to live young, rather than lay eggs as most other insects do. As pitchmen are so fond of saying, “But wait, there’s more!” A winged male will locate a parasitized host in which the adult female’s head is partially extruded; he will mate with her extruded head, and then depart. The fertilized eggs in time spill into the female’s body cavity and will develop inside of her, eventually becoming first-stage larvae. These first-stage larvae are highly active and emerge through the canal in the mother’s head, dispersing into the environment to look for new hosts. Once a new host is found, the twisted-wing larva uses digestive enzymes to effectively “bore” its way into the host’s body where it then molts to a greatly simplified, legless, and largely quiet larval form, gradually extracting nutrients from its victim. Eventually, developing males extrude from the host to form a pupa and then later an adult, while females repeat the cycle undertaken by their mothers.

  When first discovered and described, the twisted-wing parasite Halictophagus curtisii was presumed to victimize sweat bees of the genus Halictus, with this assumed biology reflected in the scientific name, which literally means “eating Halictus.” However, it was later discovered that they instead parasitize planthoppers and thorn bugs and relatives of these groups, leaving the generic name quite a misnomer. From John Curtis, British Entomology (1823–1840).

  HYMENOPTERA

  Ants, bees, and wasps are all members of the Hymenoptera (hymenos meaning “membrane” in Greek), which comprise one of the four “mega” orders of insects. Hymenoptera number over 155,000 species and are one of those groups that remain grossly underestimated in terms of their total diversity—it could double in size once a full accounting is completed. Few realize it, but ants and bees are merely modified wasps, and so one might simply say that this is the order of wasps. The big theme in wasp evolution is that of parasitism, with parasites comprising over 75 percent of the species. The most primitive wasps, however, feed exclusively on plants as la
rvae, sometimes forming large aggregations and becoming injurious forest pests. Plant-feeding species such as wood wasps and sawflies—so named because of the sawlike ovipositors they use to place eggs within stems or other plant tissues—account for only eight thousand species. These do not have the archetypical “wasp waist”; instead the abdomen is tightly adjoined to the thorax.

  The order Hymenoptera includes the ants, wasps, and bees. Many hymenopterids are capable of stinging, such as the majority of species (from varied families) depicted here, although ironically, the one at center with the long ovipositor is actually a parasitoid wasp (Bathyaulax kersteni) and does not sting. From Carl Eduard Adolph Gerstaecker, Baron Carl Claus von der Decken’s Reisen in Ost-Afrika in den Jahren 1859 bis 1865 (1873).

  Cuckoo wasps (family Chrysididae) such as these often display brilliant metallic colors and, much like pill bugs, can roll themselves into a tight defensive ball when attacked. From Amédée Louis Michel Lepeletier, comte de Saint Fargeau, Histoire naturelle des insects (1836–1846).

  Cuckoo wasps number over three thousand species worldwide and, like the birds they were named after, many are “cuckoos” that lay their eggs in the nests of other wasps—although some are specialized parasites of stick insects or sawflies. From Donovan, Natural History of the Insects of India.