Innumerable Insects

by Michael S. Engel

  Flowers come in all shapes, colors, and sizes; they beautify our deserts, prairies, forests, and even tundras. We grow flowering plants for food, medicine, clothing, and simply for enjoyment. Horticultural societies abound for fanciers of nearly all flower varieties, from roses and violets to peonies and begonias. For all this variety, pleasure, profit, and sustenance, we owe thanks to the simple act of pollination. Pollination is the process by which pollen—the grains of which encapsulate the male gametes of the plant—is transferred to a flower’s stigma, the female reproductive organ. Some plants rely upon the wind or gravity to achieve pollination. Many flowering plant species, however, employ an animal vector to transport the pollen from one plant to the other. The action of this animal vector is usually inadvertent from the animal’s perspective. An insect, for example, may visit one plant, and get pollen stuck to its body as it navigates about within the flower. Then, upon the insect’s arrival at the next plant, some of the transported pollen is incidentally transferred to its intended destination. Although some flowers are capable of pollinating themselves, having both male and female parts on the same plant, they may still rely upon an animal to move the pollen to the stigma.

  The impressive birdwing butterfly Ornithoptera priamus—named by Carl Linnaeus after the mythological Greek king Priam of Troy from the Trojan War—is an impressive pollinator across Papuasia and northeastern Australia, with wingspans up to 8.6 inches (21.8 centimeters) across. From Edward Donovan, Natural History of the Insects of India (1838).

  A diversity of pollinating carder bees (family Megachilidae), males of which can be quite territorial. Carder bee nests are lined by a “froth” of plant hairs that females scrape from leaves. From Christian Gottfried Ehrenberg, Symbolae Physicae (1828–1845).

  How critical is animal pollination? Of the approximately 300,000 species of flowering plants, about 90 percent of them utilize animal vectors. Of the 200,000 species of animals that serve as pollinators, about 1,000 of these are birds, and bats, and other mammals. The remaining 199,000 species of pollinators are insects. Pollinators are responsible for 35 percent of global food production, with 75 percent of our most important food crops relying entirely on such pollination. Every third bite of food you take is owed to the action of some pollinator. An oft-quoted (and apocryphal) prediction attributed to Albert Einstein (1879–1955) claims that the human race would have but four years to live after the disappearance of bees. While Einstein likely never said anything of the sort, there is considerable merit in the sentiment. In fact, the origin of this saying stems from Maurice Maeterlinck (1862–1949), an acclaimed Belgian playwright and controversial “entomologist” who somewhat notoriously plagiarized a famous work on termites in 1926. Maeterlinck did write several philosophical essays on entomological subjects, one of which, Le Vie des Abeilles (The Life of the Bees) (1901), emphasized the ecological important of bees. In the essay, he lauded “the venerable ancestor to whom we probably owe most of our flowers and fruits (for it is actually estimated that more than a hundred thousand varieties of plants would disappear if the bees did not visit them), and possibly even our civilisation, for in these mysteries all things intertwine.” Such a statement is not hyperbolic, and without pollinators our world would indeed wither and die.

  NECTAR, FRAGRANCE, AND WARMTH

  Insects are not altruistic. They do not engage in this service for the benefit of the flower, although the success of the plant will mean the continued availability of the resources the insects seek, and thus perpetuate their own survival as well as that of the host plant. Insects principally visit flowers for some food reward, typically nectar, a sugary fluid secreted by many flowers in order to attract potential pollinators. We, too, consume nectar, but in its more processed form as honey. Honey bees collect nectar and pollen from flowers, mix it with their own enzymes, and concentrate it through evaporation, transforming it into the sweet substance we crave so eagerly as to support a multibillion dollar global industry. The Food and Agriculture Organization of the United Nations reported that in 2013 the United States alone imported about $500 million worth of honey, and this is the result of merely one product from one insect species. Considering more broadly the impact of honey bee pollination as it relates to our insatiable diet of fruits and vegetables, this singular species contributes $15 billion dollars to the American economy, according to the United States Department of Agriculture. All of this from the action of one insect pollinator—and we have not even mentioned the full host of other insect pollinators: butterflies, moths, flies, beetles, wasps, and even tiny, unseen thrips. If insects disappeared, then nearly all pollination would cease and our world would wither. Keep this in mind the next time you wonder whether or not insects are vital to our health and security.

  Nectar is not the sole reason an insect may visit a flower. Some insects visit to collect floral oils and fragrances, while others consume the pollen itself. One particularly interesting insect-floral association is demonstrated by the orchid and its bees. Orchid bees as a group encompasses approximately 250 species of fairly robust and often brightly metallic colored bees found throughout tropical South America and Central America. Male orchid bees visit orchids (which have no nectar) to collect fragrant compounds secreted by the flowers. As the male bee goes about his task, the orchid attaches a purse of pollen to his back; the pollen is distributed to other flowers as the bee goes from orchid to orchid. The male bee packs the fragrant compounds into a specialized gland within his hind legs, and then he synthesizes the compounds into a pheromone to attract females. The orchids are pollinated and the male orchid bee gets the sweet perfume he requires in order to find a mate.

  While most bees are pollinators, such as the large carpenter bees (genus Xylocopa) depicted here (top and center rows), hundreds of bees are cuckoos, such as the male and female of Epeolus variegatus (bottom row), which invade and lay eggs in the nests of pollen-collecting bees. From Amédée Louis Michel Lepeletier, comte de Saint Fargeau, Histoire naturelle des insects (1836–1846).

  Many bees are generalists, visiting a wide variety of different flowers for pollen and nectar, while others are narrowly specialized to visit particular genera or species of flowers. Carpenter bees (top) are generalists; while orchid bees (center) visit orchids to collect fragrant oils used in attracting a mate; and oil-collecting bees (bottom) have particular combs on their fore- and midlegs to scrape plant oils from their floral hosts, which they then mix with pollen to feed their larvae. From Rothschild, ed., Musée entomologique illustré.

  Much farther north, some arctic flowers that bloom during the region’s short, cool summers concentrate the rays of the sun to heat their organs, and pollinators such as flower flies, dagger flies, and even mosquitos (yes, mosquitos can be pollinators!) visit these flowers in order to take advantage of the warmth. Flowers can also serve as a secure place in which to roost for the night, and there are many insects that can be found sleeping within the protective folds of petals. The benefits of flowers to insects are therefore manifold.

  The pollinators most familiar to us are bees, butterflies, and moths. Among these, butterflies perhaps have historically grabbed the most attention—their large, colorful wings and bobbing flight as they flit from flower to flower have long made them the favorites of naturalists. It is no surprise that sublime paintings of butterflies on their host plants have dominated the pages of historical works, such as the sumptuous monographs of Edward Donovan (see pages 188-189) or many other naturalists. Among the bees, however, we tend to overlook the majority of these preeminent pollinators. While we love to sing the praises of honey bees and bumble bees, they are merely a small fraction of more than twenty thousand species of bees throughout the world, most of which are solitary. These include digger bees, sweat bees, carpenter bees, fire bees, nocturnal bees, and countless others that have not been so fortunate as to receive a common label. In North America alone there are nearly 4,400 species of bees, of which the common honey bee is just one, and it is not native;
it was brought by English colonists to the nascent Virginia Colony in 1622. The thousands of native North American bee pollinators are just as important as the imported honey bee, and some species are even more effective than honey bees, owing to their evolution with the native flora. For example, solitary orchard bees and leafcutter bees can dramatically increase yields, with entire industries now centered around such species.

  Butterfly pollinators are famous for their showy colors, which can be dramatically different depending upon the side of the insect viewed. Here, amid some of Edward Donovan’s Indian butterflies from his Natural History of the Insects of India, this is exemplified by the wings of the orange albatross butterfly (Appias nero), whose wings are bright yellow on their underside (left) and reddish orange when viewed from above (top).

  Bees are preeminent pollinators, with over twenty thousand species found worldwide, and here represented by a diversity of Malagasy bees from Henri de Saussure’s volume on ants, bees, and wasps from Histoire physique, naturelle et politique de Madagascar (1890).

  While butterflies and bees are crucial to flower fertilization, critical pollinators are also to be found among flies, beetles, and thrips; for certain flower species, these insects are infinitely more vital. In fact, flies are perhaps second only to bees as vital pollinators, and quite spectacularly, the largest flowers in the world are pollinated by flies and beetles, not butterflies or bees. The two most massive flowers are both native to Sumatra and, when in bloom, smell of rotting flesh. The so-called corpse flower, or Rafflesia arnoldii, can measure 3.28 feet (1 meter) in diameter and weigh nearly 25 pounds (11.34 kilograms). The unrelated titan arum, Amorphophallus titanum, produces a phallus-shaped inflorescence, or cluster of flower structures, that can reach to 10 feet (3 meters) in height, which blooms for the first time after approximately a decade of growth. The stench of these flowers attracts the flies and beetles that are the principal pollinators for the plants.

  Although bees and butterflies get all the attention, true flies (order Diptera), such as this diversity of flower flies (family Syrphidae), include some of the most important pollinators. From Biologia Centrali-Americana. Insecta. Diptera. (1886–1903).

  Beetles, such as these colorful scarabs (family Scarabaeidae) from John O. Westwood’s The Cabinet of Oriental Entomology (1848), are often excellent pollinators of flowering plants.

  THE ARMCHAIR ENTOMOLOGIST

  Edward Donovan was the epitome of an eighteenth-century armchair naturalist, and aside from excursions to Wales or the English countryside, he remained well ensconced at home in London. Born in Ireland in 1768, he became an insatiable collector, purchasing specimens at auction that were being brought back from abroad. Donovan eventually built up a considerable private collection, which he opened to the public in 1807 as the London Museum and Institute of Natural History. Eager to share his knowledge on natural history, particularly exotic species, Donovan published and illustrated various books on botanicals, birds, fishes, and, most notably, insects. Donovan’s association with several learned societies of the day gave him access to even more material, including extensive reference libraries to consult, and he was supported for a time in his efforts by Sir Joseph Banks (1743–1820), the famed explorer, botanist, and patron of many naturalists for nearly half a century. Donovan published three particularly important books on insects: An Epitome of the Natural History of the Insects of China (1798) and similarly titled works on the insects of India (1800) and New Holland (Australia) (1805).

  Since Donovan relied on others for much of his knowledge of foreign insects, errors crept into his books, such as depictions of a butterfly species from the West Indies that he incorrectly attributed to India. Nonetheless, while most monographs concerned themselves with accounts of European insects, Donovan’s books were a refreshing departure. His devotion to his craft was total—he wrote, drafted, engraved, and ultimately colored all of them by hand. His artistic talents were considerable, and he often undertook commissions, particularly for floral paintings.

  Once threatened, the blue emperor swallowtail butterfly (Papilio ulysses) is now thriving across northeastern Australia and the islands of Southeast Asia owing to conservation efforts. While the underside of its large wings—wingspan approximately 4.1 inches (10.4 centimeters)—are brown, concealing the insect when at rest, the upper surface is a broad splash of vivid blue. From Donovan, Natural History of the Insects of India.

  The great Atlas moth (Attacus atlas), is one of the largest of all Lepidoptera (moths and butterflies), with a wingspan slightly over 9.8 inches (25 centimeters), and can be found commonly across the Malay Archipelago and elsewhere in the tropical forests of Southeast Asia. From Donovan, Natural History of the Insects of China (1838).

  Like many whose obsessions are left unchecked, however, Donovan eventually fell on hard times. His purchases of specimens became quite costly, and he quarreled with publishers whom he felt had dealt with him wrongly—he sold them 50 percent of the rights to his books, but they retained a far greater portion than this. Add to this an economic depression brought on by the government’s campaigns against Napoleon, and by 1817, Donovan had to close his museum. Heartbreakingly, in 1818, he was forced into the sale of his treasured collection at auction. Once a frequent buyer at auction, Donovon was now the seller. In 1833, he penned a plea to readers for help in suing his publishers, but no one came to his aid. Even in financial despair, Donovan kept publishing, eventually leaving his family destitute when he died in debt in 1837. After his death, John O. Westwood (see pages 50-53 ) revised Donovan’s books on Indian and Chinese insects. Owing to the use of thicker layers, albumin glazes, and metallic paints, the newly reproduced plates were more vibrant than Donovan’s originals. These volumes are among the most beautiful and artistic renderings of butterflies, moths, and other exotic insects of the period. It is sad to think that today, when Donovan’s books turn up at auction, they fetch many thousands of dollars—even single paintings by him can go for such prices—and yet his work failed to bring him sufficient support in life as to attend to his family’s needs and further his entomological passions.

  The fantastical Southeast Asian rice paper butterfly (Idea idea) originally described by Linnaeus. These large pollinators are difficult to miss with their stark black-and-white color and wingspans up to 5.2 inches (13.3 centimeters). From Donovan, Natural History of the Insects of India.

  Sometimes plants certainly get one over on insects. Producing nectar and other rewards for insects can come at some price to the flower, as these activities require water and sugars that could otherwise be used to make more seeds; many plants have evolved sneaky ways of getting around this problem. Some orchids have flowers that superficially resemble the patterns of female bees or wasps and remarkably produce chemical scents that mimic the odors of such females. For example, species of the orchid genus Chiloglottis produce pheromones similar to those of a group of stinging wasps in the family Tiphiidae. Male tiphiids approach the flowers, whose shape and patterns similarly mimic female wasps, and attempt to mate. The landing of the male on the orchid flower triggers the plant to glue a packet of pollen to the wasp’s back or head, and the pollen is then picked up by the next flower the male attempts to mate with. In this way the flowers are pollinated while the male wasps are duped.

  True flies include some of the more spectacular of specialized pollinators, such as Moegistorhynchus longirostris at center, a fly whose proboscis is the longest relative to its body size among insects. This tangle-veined fly is an important pollinator that has coevolved alongside long-tubed flowers in western South Africa. From Félix-Edouard Guérin-Méneville, Iconographie du règne animal de G. Cuvier (1829–1844).

  The head and extended tongue of the four-spotted moth (Tyta luctuosa) with various pollinia of the pyramidal orchid (Anacamptis pyramidalis) attached. From Charles Darwin, The Various Contrivances by Which Orchids Are Fertilised by Insects (1895 [1862]).

  SPECIALIZATION

  Some insects are
generalist pollinators, visiting a wide range of flower species as they seek nectar and pollen, the honey bee being a paramount example of such indifference. Others are specialized to feed on only a subset of certain flowers, either within a particular genus or even family of plants. More specialized yet are those insects that can survive only through visits to a single plant species, and often the plant is similarly reliant on this one insect for its own persistence. The specialization between flower and insect can be great. A famous example is Morgan’s sphinx moth, Xanthopan morganii, and its eastern African and Malagasy orchid, Angraecum sesquipedale. Charles Darwin spent time researching insect pollination for his 1862 book, Fertilisation of Orchids. He received flowers of A. sesquipedale from a horticulturist and was surprised to note that the peculiar nectary (the gland that secretes nectar) of the flower was nearly 1 foot (30 centimeters) in length. Darwin concluded that there must exist a specialized moth with a greatly elongate proboscis capable of reaching into the nectary. Darwin’s collaborator in publishing a sound mechanism for evolutionary processes, the explorer Alfred Russel Wallace (see page 178), later wrote in 1867 that specimens of X. morganii had elongate mouthparts and were perhaps the visitors of these flowers, refining Darwin’s prediction that in Madagascar there must be a form of this moth species capable of reaching so deep into the nectary. Indeed, such a form was discovered in 1903, and it was described as the subspecies X. morganii praedicta, corroborating the hypotheses put forward by Darwin and Wallace about forty years prior.