One evening in 1966 near Lake Placid, Florida, one of North America’s most beautiful moths flew into the web of a great orb-weaving spider. Trapped moths usually struggle desperately to escape, but this magenta-hued beauty, its wings boldly spotted with black-in-white bull’s eyes, lay unperturbed as the spider crept ever nearer. When it reached the moth, instead of delivering a killing bite, the spider hesitated for a moment, and then gently cut by turn each of the silken threads holding the insect, until it fluttered free.
We might be tempted to read into this story a Beauty and the Beast–like allegory. And in a way it is, for the moth’s beauty provides very real protection from the many beasts it encounters. Yet as Thomas Eisner, who witnessed this event, would discover, that beauty acts more by way of warning than heart-softening appeal, for it informs potential predators that beneath its skin-deep veneer flows poisonous blood.
Eisner is a professor of chemical ecology at Cornell University. One of the world’s eminent natural historians, he is also an award-winning filmmaker, the author of numerous landmark scientific publications, and a recipient of the US National Medal of Science. His latest book, For Love of Insects, tells the story of his research, along the way revealing how hard-won his acclaim is. His single observation of the spider and the beautiful moth, for example, led to thirty years of painstaking research on the chemical defenses of the ornate moth (Utetheisa ornatrix), revealing a life of extraordinary intricacy and complexity.
The moth’s chemical protection is acquired from its sole source of food, the rattlepod bush (Crotalaria spp.). Plants of the rattlepod genus produce alkaloids in order to defend their leaves and seeds from herbivores. The toxin can kill most animals, but the larva of the ornate moth is immune—indeed it prefers to feed on the plant’s most poisonous tissues, such as its seeds. The alkaloids thus acquired are stored in the insect’s blood, and after the caterpillar has transformed itself into a glorious moth, the toxins are deployed in frothy blood that is extruded from near its wingbases.
Understanding how the moth stores and uses its toxin for defense was only the beginning of Eisner’s discoveries. Through a series of ingenious experiments that involved rearing some caterpillars on alkaloid-free food, he discovered that the toxin is essential to the moth’s sex life. Males reared on a toxin-free diet seemed normal in every respect, yet they received a brusque brushoff from females whenever they attempted copulation. High-speed photography revealed that, when intent on copulation, male moths extend two large brush-like structures from a cavity called the cloaca, which are used to stroke the female for a few milliseconds prior to copulation. High-resolution microscopy showed that the brushes consist of soft, hollow scales that are filled with a derivative of the alkaloid toxin. Only those males that tar their mates with a toxic brush, so to speak, get to have sex. This peculiar behavior led Eisner and his colleagues into a detailed investigation of insect sex life, the findings of which are, to the naive reader, often as startling and outlandish as anything invented in science fiction.
The ornate moth is, by Eisner’s account, the sexual marathon champion of the insect world. Couples engage in the sexual act for up to nine hours at a time, which, for a creature that survives in its adult form for only a few weeks, is a lengthy coitus indeed. Such extended couplings seem to be necessary so that the male can transfer his voluminous ejaculate to his mate. This comprises an astonishing 10 percent of his total body weight; should human beings be given to producing an equivalent volume, sex would be a messy business indeed, for around eight liters of fluid would be involved. Sperm forms only a small fraction of the fluid, by far the greatest part consisting of nutrient and the toxin that is so avidly consumed by the caterpillar. Within minutes of receiving the alkaloid contained in the seminal fluid, the females have transferred it into their blood, rendering themselves immune to most attacks. Then, when the time comes to lay eggs, the female withdraws some of the stored toxin and secretes it within the eggshells, thus defending her offspring from attack as well.
With sex offering such immense benefits, female ornate moths have healthy libidos. They will mate with as many chemically defended males as possible—twenty-three is the record so far. Yet even if she has multiple partners, all of a female’s eggs are fertilized by a single male. He is not the first one she mates with, or the last, but the largest. Just how the female selects his sperm remains a mystery, but Eisner’s colleague Craig LaMunyon has demonstrated that the mechanism may be under conscious, probably muscular, control. He discovered this by anesthetizing female moths after copulation, a procedure which rendered them unable to discriminate between the sperm of various males, and ensuring that their eggs had many fathers.
Insect lives are all about the basics—food, sex, and death—yet the ways they have evolved to cope with life’s challenges are often so ingenious and intricate that our human lives can look uncomplicated in comparison. Because chemistry plays such a large role in their existence, much of that complexity is invisible, becoming evident to us only through detailed and intricate experimentation.
Gifts of love such as the ornate moth’s seminal toxin are not uncommon in the insect world. A more widespread and obvious strategy for acquiring toxins, however, involves pred- ators that derive it from their prey, and that strategy sometimes entangles humans in the weird world of insect chemistry. An astonishing case came to light in 1893, when a certain Dr. Meynier, attached to a French military force serving in northern Algeria in 1869, wrote about having found his chasseurs d’Afrique suffering from an embarrassing complaint. The men were doubled up with stomach pains, thirst, and painful urination, but their most surprising discomfort was érections douloureuses et prolongées. Given this last symptom the afflicted soldiers were perhaps somewhat impatient and perplexed when Dr. Meynier asked them what they had been eating. Their answer, however, gave the doctor the clue he needed, for the men had been at the local river catching frogs to make that Gallic delight cuisses de grenouille (frogs’ thighs). Close examination of the frogs’ stomachs revealed that they had been eating blister beetles (family Meloidae)—the source of the famed aphrodisiac Spanish fly. Rather disappointingly, and despite the érections prolongées suffered by the soldiers, Eisner informs us that the aphrodisiac qualities of cantharidin (the principal ingredient of Spanish fly) are, in the case of humans at least, greatly exaggerated.
There are insects, however, known as cantharidiphiles, which while they cannot synthesize cantharidin, find it to be a true aphrodisiac. These creatures are irresistibly attracted to the chemical, and will travel vast distances for a few grains. Some must kill to obtain it, while others lick the corpses of blister beetles (the only known primary source of the chemical) to satiate their craving. A few even sell their bodies on the insect sex market for it. One of the larger cantharidiphiles to be found in the US is a handsome red-and-black creature known as the fire-colored beetle (Neopyrochroa flabellata). Eisner characterizes the species as “utterly shameless and [they] usually ‘go at it’ the moment a pair is introduced into a petri dish.” Looking at their behavior in greater detail, however, Eisner discovered that their mating is not as straightforward as it seems. When male and female meet, the first thing the female does is to grasp her partner’s head and insert both of her biting jaws, or mandibles, into a cleft that runs across his forehead. The cleft looks as if it might have been wrought by a blow from a miniature axe, and deep within it a glistening fluid can be seen. This substance contains cantharidin, and if the female is not satisfied after imbibing at the groove, mating will not take place.
The amount of cantharidin she obtains this way is minute—just 1.5 percent of the male’s store—and Eisner’s team was at first uncertain why a female would sell sex for such a paltry return. The cantharidin in the groove, they learned, was just a foretaste of what was to follow, for if there is cantharidin in his groove, a male will deliver a goodly dose in his ejaculate. In effect, the “taste” of the aphrodisiac in the groove acts as the male’s bona fides. Obtaining a store of cantharidin is vital to the virgin female fire-colored beetle, for she possesses none herself, yet it is essential to protect her eggs from predators.
Much of Eisner’s fieldwork has taken place at the 1,500-acre Archbold Biological Station near Lake Placid, Florida. This wonderland of biodiversity is the gift to biologists of one of America’s great explorers and philanthropists. During the 1930s Richard Archbold sponsored and participated in a series of expeditions to New Guinea, which were conducted under the auspices of the American Museum of Natural History. They included some of the most extended and significant biological expeditions of the twentieth century, and the results of the expeditions continue to be published. Archbold acted as pilot, flying his frail aircraft into true terra incognita. In 1938 he took his twin-engined “flying boat” Guba over the Baliem Valley in West New Guinea (now part of Indonesia). He later trekked into the region, becoming the first outsider to encounter the remarkable Dani people and their “Shangri La” valley. This was a landmark discovery, for never again would such a large population be brought into contact with the outside world. I was intrigued to read of the wonderful work Archbold supported at Lake Placid, and of his foresight in acquiring such a large swathe of a biologically valuable and threatened region.
Eisner’s work has also taken him to the deserts of Arizona, to Australia, and to bogs and woodlands near his home in Ithaca. Wherever he travels, however, he seems to be eternally on the lookout for a clue that will lead him to another chemical discovery. Complex investigations into the life histories of creatures that most of us would unthinkingly crush underfoot have been a lifelong obsession for Eisner. Born into a German-Jewish family in Berlin in 1929, he and his parents were forced to flee Nazism, first for destinations in Europe and then, as the threat grew, to Uruguay. For Love of Insects is partly biographical, offering intriguing insights into the kind of person who would devote his life to such work. In explaining his own enthusiasm for insects, Eisner reveals himself to be a devotee of his colleague Edward O. Wilson’s biophilia hypothesis—the idea that humans are naturally drawn to living things and are born with an inherent love of them. What is needed to “trigger” the biophi- lic response, Eisner speculates, is the opportunity to interact with nature during childhood. He suggests that this fac- tor explains why there are relatively few Jewish biologists, for the ghettoes of Europe and great cities like New York offer few opportunities for children to explore natural ecosystems. In Eisner’s case Uruguay, where he lived between the ages of eight and eighteen, offered him a chance to observe nature firsthand. It provided a sort of natural bonanza, for the country is exceptionally rich in biodiversity.
I am not entirely convinced by Eisner’s reasoning in this regard, for even as a very young child in Europe he was clearly fascinated by wildlife. He vividly recalls seeing, at age seven, a butterfly collection kept by a Dutch uncle. Indeed so focused was he on insects that despite what was clearly a stressful early childhood, his account of his family’s forced travels reads as little more than a series of opportunities to collect and observe invertebrates. This suggests to me that Eisner’s interest in insects was largely inherent, and thankfully complemented by a highly original and ingenious mind in which deductive reasoning, patience, and a love of gadgetry have combined to allow him to undertake complex investigations. He also has a remarkable sensory capacity, being, as he puts it, “nasal” from the start:
My parents recalled that when I was little I could tell from the scent that lingered in the coat closet in the morning that my grandmother had visited the night before. But now, as a teenager, I was coming to realize that I could really learn things from my nose…. I learned to sniff insects carefully.
Thomas Eisner’s father, Hans, also had exquisitely sensitive nostrils, which he employed in his leisure moments by creating perfumes, skin lotions, and colognes for his family and friends. In 1958 Hans retired to Ithaca where he joined his son’s lab and employed his chemical talents on insect experimentation. Indeed the number of collaborations Thomas Eisner has formed with a wide variety of people—including photographers as well as biochemists—is both astonishing and a testimony to his social skills.
Eisner’s first experiments in chemical entomology were undertaken at a very tender age, while he was still in Uruguay. They concerned the bicho peludo, or hairy beast, a caterpillar that is covered in hairy spines that can inflict instantaneous pain and severe systemic reactions. Eisner recalls:
I used to raise bichos peludos and noticed that they lacked spines on the belly surface, so I concluded that I risked nothing if I could somehow get them to crawl onto my hand without touching the spines. I mastered the technique and would often induce panic among my buddies by approaching them menacingly with arms raised and a bicho peludo on each hand. I managed to scare even the neighborhood bully in this fashion. Evidently, if I made myself obnoxious enough, I too could emit warnings that were heeded by others. I remember experimenting with the spines. I cut them with scissors and noted that they were hollow and filled with fluid. I placed droplets of the liquid on my skin and quite foolishly also on my tongue, only to find to my surprise that this caused no pain. Needless to say, I conducted these experiments in utter secrecy.
After being rejected from a series of colleges (including his own, Cornell—he keeps the rejection slip proudly framed on his office wall), Eisner finally entered Harvard University where, in 1951, he met Edward O. Wilson, whose “ascendancy into the ranks of the truly great in science was then already foreseeable.” In 1952 the pair drove 12,000 miles across the US in a “geriatric Chevrolet,” studying insects and cementing a relationship that has endured to this day. In a handsome foreword to the book, Wilson writes of Eisner as “the modern Fabre,” after France’s pioneer observer of insect life, which is high praise indeed in entomological circles.
Despite its highly enjoyable reminiscences, For Love of Insects is first and foremost a scientific work. It is filled with schematic illustrations of chemical compounds and technical drawings that act as vital visual aids in understanding the phenomena under discussion. But it also includes glorious close-up photographs of insects. Some, such as one of the pupa of a moth shown on page 400 (see illustration on page 24), are as beautiful as they are revealing. It is clear to anyone who has read Eisner’s book that the delicate golden net surrounding the helpless pupa must be stocked with defensive chemicals, for the physical deterrence it offers is flimsy indeed.
For Love of Insects is also packed with strange-but-true facts. Readers may be both surprised and discomfited to learn that ant lions (which build their pit-traps under eaves and in other dry places) have no anus and so cannot defecate until they are transformed into beautiful lacewings. And who would have guessed that the bombardier beetle expels its chemical defenses while boiling hot, in pulsed spurts at the rate of 500–1,000 per second? Further cause for astonishment is provided by the caterpillar of the spicebush swallowtail butterfly. It possesses the most lifelike false “eyes” on its neck, which seem to follow the observer wherever he goes. The effect is achieved by the teardrop-shaped “pupils” of the false eyes, a discovery that, as René Auberjonois’s The Italian Lady illustrates, was made by artists long before scientists ever understood the ruse.
Eisner’s book will not appeal to everyone, for it assumes considerable prior knowledge of chemistry, entomology, and biology in general. A reader seeking common names among the thickets of Latin binomens will search in vain, as will those in pursuit of sustained storytelling. Instead, the reader will encounter a catalog of scientific investigations, leavened here and there with insightful autobiography. The work’s chief value clearly lies in its documentation of a pioneering science, for Eisner’s team has fundamentally reshaped the field of chemical entomology. In many ways For Love of Insects is a beginning rather than an end—“an account of a nascent field of biology,” Wilson calls it.
This book is filled with unsolved mysteries and clues for the young researcher, with leads discovered but not followed up for sheer lack of time. Even basic matters remain unknown. Are blister beetles, for example, really the sole source of cantharidin? Many insect species depend upon it—too many perhaps for blister beetles alone to supply—yet thus far no other sources have been identified. Future discoveries promise to be both prolific and spectacular, and judging from the recent growth of investment in biotechnology, they will be of ever-greater importance to the world.
March 11, 2004