Butterfly People

by William R. Leach

  But why did the black form have the upper hand (or wing)? Weismann thought sexual selection was the answer—that yellow males, for some reason, preferred black females. Edwards, however, had observed many yellow males impregnating both yellow and black females “on the wing”; moreover, he noted, “the males may be seen coquetting with the yellows as freely as with the blacks.” He proposed, instead, that the black female was succeeding (or would succeed over time) because it had an “astonishing energy” and because its blackness mimicked the blackness of other swallowtails, especially of the pipevine swallowtail, a mostly southern species with a bad taste and smell that repelled birds. The yellows, on the other hand, “are captured by birds and other enemies during the day” because of “their gay colors,” which “render them an easy prey.”16 Edwards illustrated these arguments with three marvelous plates by Mary Peart and Lydia Bowen, more than he ever devoted to any other American butterfly. The first plate showed the tiger’s life history (caterpillar, egg, pupa), plus that of the females, black and yellow. The second plate pictured the black female and the “two sexes of the yellow form together,” the first such representation published, and the final plate depicted a yellow male in the company of three intermediate females, one half black, half yellow, the other two with suffused mixtures of yellow and melanism, each, perhaps, a creation of the belt of dimorphism.

  Edwards always looked to the early stages to establish specific or generic identity, the preoccupation with wing color seeming to give precedence to the imago. “I can’t help thinking,” he explained to Scudder, “that the first three stages are the ones in which [generic] affinities are to be sought, rather than in the fourth.” But he decried other naturalists’ reliance for identification of species or genera on butterfly wing venation, on arrangement of veins on the wings, or on, God forbid, the genitals. “I have very little respect for wing classification,” he wrote Scudder, who, like Grote, considered wings and genitals worthy of reflection; in 1888, he declared, “One caterpillar is worth fifty genitalia for the purposes of distinguishing obscure species.”17

  Like Darwin and Weismann (and before them Buffon and Humboldt), Americans practiced a broad ecology in which “climate and environment,” as Edwards put it, must be taken into account to understand “the descendants of a common parent-form.” Grote called it “the phylogeny of species,” writing, “The crucial test of our modern idea of species lies in the demonstration of the fact that, in the whole life history, the cycle of reproduction is now distinct. To the establishing of this fact repeated observations are often necessary. The whole condition under which the form is produced must be understood.” We must deal with “geological conditions” that “have played a part in the evolution of species,” he noted. “For students of butterflies and moths the criterion of species must lie in knowledge of the whole life of the insect.”18 Butterflies did not come out of nowhere fully dressed for business, Grote believed, but “adapted by change of habit to altered circumstances,” in the face of countless indignities, and in response to volatile weather and temperatures, earthquakes, and shifting land masses.19 Those insects that met these challenges endured, Scudder wrote, their “advantageous variations perpetuated and intensified by the survival of the fittest, through the law of inheritance.”20

  Edwards saw vast geologic variability in temperatures, cold to hot, writ small in the lives of polymorphic and dimorphic butterflies, the butterflies telescoping evolution, bearing ancient history in their bodies, revealing how modern species emerged. He believed that butterflies were, in Scudder’s words, extremely “sensitive to the least influence from the outside.” A sudden drop in the temperature might strike down entire populations with devastating effect; a simple sustained frost felled many billions. “Winter, indeed,” observed Scudder, “is the prime cause of variety in nature.”21 A shift from dry to wet seasons could kill butterflies, William Doherty observed in India, unless the butterflies could make adjustments.22 Grote noted the impact of what he called “all the phenomena of climate and temperature” on the geographic distribution of moths and butterflies, and both he and Scudder wrote at length of the great glaciers that dropped down from the north to remake the butterfly universe. But even more deadly dangers lurked to demolish butterflies and moths at every stage of their existence—dangers that were especially harsh for butterflies, which did no harm to any other living thing.

  “The life of a butterfly,” wrote Scudder in “The Enemies of Butterflies,” “is one of imminent danger from birth, nay before birth, to death.” He was thinking here of such predatory species as the “creeping crawlers”—mites, ants, and spiders—in pursuit of quick meals, or the “pirates of the air,” as Edwards observed, the dragonflies, bees, and wasps that “pounced upon” butterflies “as do hawks on small birds, bearing away their prey to be devoured at leisure.”23 Butterflies had even graver foes, notably the remorseless critters Scudder named “the wandering buccaneers” of nature’s realm. Today, scientists call these buccaneers “parasitoids” and believe that close to two million species of them may exist, equal to 20 to 25 percent of all insects, or, put even more impressively, to about one-tenth of all animal species.24

  Parasitoids are not parasites, though that’s what nineteenth-century naturalists, including Scudder, called them. Parasites seem almost sweet-tempered by comparison to parasitoids, for parasites do not kill their hosts (the term is Greek for “unwelcome guest”).25 Parasitoids, on the others hand, are killers, some adapted to devour only eggs, others to eat the larvae or pupae. Tiny flies lay their eggs on the surfaces of larvae; the hatchlings will later eat the larvae from the outside. Others feed secretly from within, killing the host only when the parasite itself starts pupating. Many have an aptitude for targeting prey, like one female parasitic fly described by Archibald Weeks, a Brooklyn moth specialist, in an 1887 issue of Entomologica Americana, an influential Brooklyn journal on insects. Weeks watched this particular fly with a hand lens as it dropped a single egg delicately between the “eyes” of its prey—in this case, a moth caterpillar feeding on a leaf. Soon the fly added other eggs to the same spot; “so gently was this done,” Weeks noted, “that the larva did not at first appear to be disturbed, but presently the adhesion of a foreign substance seemed to annoy it and it scraped its eyes against the bitter edge of the leaf in a vain effort to rub off the barnacle-like ova.”26 George Hulst, a Brooklyn moth specialist, compared these insects to the Grecian horse within the walls of Troy. Some parasitoids even parasitize the butterflies’ parasites.

  Shown here is an unusual grouping of parasitoids from Scudder’s Butterflies of the Eastern United States and Canada, vol. 3, plate 88. Scudder called them “evil-looking” and believed they were the most dangerous of all butterfly enemies. Note the ichneumon wasps 1 and 2, as well as the parasitized pupa of a butterfly (13), full of holes left behind by recently emerged wasps or flies whose eggs had earlier been laid inside the pupa, later to hatch and, then, to eat the pupa from the inside out.

  Click here to view a larger version of this image.

  The most notorious parasitoids belong to the Ichneumonidae, a populous family of flies and wasps that encompass the genus Ichneumon. Slender insects with long, graceful antennae, ichneumons inject their equally long and graceful ovipositors, or egg-laying stingers, into their victims, discharging eggs that, over time, hatch inside and proceed to “live on the juices of the body,” to quote Scudder. Ever since Aristotle, naturalists had been aware of parasitoids, though only in the mid-1700s did they learn precisely what these creatures did with their time.27 Linnaeus had named the whole family Ichneumonidae; it was revised again and again by other naturalists as new species were encountered.28 By the early 1800s, extensive descriptions of the genus Ichneumon were regular features in entomological writings, appearing like some frightful specter at the carnival of life.29 Scudder said they were “evil-looking.” Darwin was unnerved to find that nothing other than natural selection—certainly not “a beneficent
and omnipotent God”—had produced such a being.30

  The term itself, derived from the Greek ikhneumon, or “tracker,” in turn, from ikhnos, meaning “track” or “footsteps,” was usually applied to wasps or flies. Alpheus Packard wrote, in the 1880s, that about three hundred species of such ichneumons had been discovered throughout the world.31 Thorstein Veblen, the brilliant American political economist and caustic critic of American capitalism, writing at the beginning of the twentieth century, seemed drawn to these insects as emblematic of a heartless universe and gleefully told tales about them, especially to impressionable undergraduates at Stanford University, where he taught briefly. According to one such student, R. L. Duffus, later a widely read journalist, Veblen explained that a caterpillar, once stung, “might know that something had happened, but not what. It would go about its business, troubled by sensations which it might attribute to an acid stomach or overwork, until the eggs hatched. Then the little ichneumon grubs would start eating the caterpillar, which, being alive, had kept fresh without refrigeration. The caterpillar would then realize what had happened, but it would be too late.” Duffus, sounding like Darwin, wrote that he himself “was inclined to think well of Nature,” but “what was one to think of the beauty of the world if such things were going on it.… If there was a God, He was letting the flies get away with murder.”32

  William Henry Edwards reared parasitoids from butterflies caught in the field, such as the red-spotted purple, the spring azure, and the hackberry butterfly.33 Of a little parasitoid he saw under a magnifying glass inserting its stinger into the eggs of a giant swallowtail, he wrote Joseph Lintner, “One would not think a fly that size would have the strength to push its ovipositor through the shell of such an egg.” He described another encounter: “I had an odd thing happen yesterday in connection with Atalanta” (the red admiral). “The small larvae which came at the tail of their generation seem frequently parasitized, and the fly comes out of the larva in the second larval stage.… Well, in the glass in which I had some cocoons, I observed a swarm of minute flies … 3/100 in. long. On examination of the cocoons, I found one which had a minute round hole near the top, and no doubt out of these little flies came. The larger cocoons have the whole top left off. This means that the parasite itself was parasitized.” Edwards put together a large collection of both “parasites” and willingly shared them with Leland O. Howard and Charles Valentine Riley. To Howard, the insects Edwards had seen were “hyper-parasites.”34

  Scudder considered parasitoids as so crucial to understanding the chain of natural life that he allotted two separate plates to them in volume 3, the only such treatment he gave to other insects besides the butterflies. He also invited Howard and Riley, both of the Department of Agriculture, and Samuel Williston, an entomologist from Yale, to submit essays on them for volume 3 of his Butterflies of the Eastern United States and Canada. Williston picked small flies as his subject of “The Dipterous Parasites,” and Howard four wasp families, including the Ichneumonidae, with special scrutiny of five or six kinds of hyperparasites he called “secondary parasites.” Charles Valentine Riley, one of the most original Darwinian biologists of his day, analyzed many tiny brown and black wasps of the family Braconidae, but he doubted the classification; with so much variation in the species, he felt, one could make no “well-marked divisions.” Study confirmed for Riley “the idea of the nonexistence of species as such in nature.” Years before, in the late 1870s, he had even tried to persuade Scudder—at a time when Scudder could not be persuaded—that nature could not be split into clear-cut species and genera: “I feel convinced that the more we understand our species, the more we are acquainted with their biology, the more we shall find they run into one another. In a natural system we never shall be able to draw arbitrary lines.”35 Still, Riley named a few, among them a tiny parasite of the red admiral Edwards had sent for him to determine: he named the species Apanteles edwardsii in honor of Edwards.36 Riley, along with Williston and Howard, did the most authoritative work on parasites and parasitoids by Americans up to this time.37

  Scudder reported, in “The Enemies of Butterflies,” that “certainly ninety-nine one-hundredths of every brood” of a given butterfly “perish before maturity” from parasitism, “and even after maturity is reached a very considerable proportion of the remainder must come to an untimely end within a day or two of birth.” The waste of life was incredible, but the most egregious damage came from the insect parasitoids. At the egg stage, Scudder observed in an essay, “The Perils of the Egg,” “the struggle for existence” becomes acute; “excessively minute” wasps and flies beset the butterfly, and out of thousands of eggs laid “by say thirty females” (and here Scudder quoted from a letter received from William Henry Edwards), “hardly twenty butterflies result.” The larvae, too, had its enemies, notably several parasitoids that had evolved to kill only larvae and nothing else. “Nearly one-third of all the butterflies described in the body of this work,” Scudder wrote in “The Enemies of Butterflies,” “are known to be attacked … by these horrid fiends.” They treated “a caterpillar” like a “peripatetic banquet hall.”38 Milbert’s tortoiseshell butterfly, a lovely small, orange-banded northern species, had many suitors, among them a fly that consumed nearly all the larvae produced at the end of the summer. “In one instance,” Scudder observed of his experiment on this “parasite,” Apanteles atalantae,

  of the twenty-five larvae which I placed in a breeding cage, only five became chrysalids. From the body of each of the others, when fully grown, a number of worms emerged and spun themselves up into small, white cocoons placed with perfect regularity side by side, forming a compact bundle, usually round in form, made up of from twenty to sixty cocoons, the whole enveloped in a cottony substance. The cocoons were in every instance spun underneath the larva; as the mass increased, the body of the exhausted larva above it was raised up from the leaf or stem on which it rested, and embraced the bundle in its curve. The larva presented us with an instance of great tenacity of life; even when every portion of its body had been honeycombed by the escape of the large number of parasites which it nourished—sufficient, one would suppose, to produce speedy death.39

  Another of the Milbert’s enemies, as lethal as this fly, “calmly suck the caterpillars in one of their retreats.” The common red admiral, wherever it roamed, was likely to come face-to-face with wasps eager for its company, one wasp attacking the larva before it “completed its very first nest,” and another overtaking it so completely that it “is often difficult,” Scudder wrote, “to procure a single butterfly from a large number of larvae taken in the open air; they are crammed full of parasitic enemies, which suddenly emerge through the skin of their victims when full grown, and spin their pure white cocoons beside the now collapsed prey.” Still another “crowded” the butterfly’s larvae “full of worms,” producing “coal-black chrysalids,” that “stood erect in their hinder ends around the corpses they have destroyed, like black tomb-stones in a cemetery.”40

  Life for butterflies was a horror show, and Scudder, along with Edwards, Grote, and others, marveled at the butterflies’ capacity to endure it. Edwards pondered: How did the rarest of American hairstreaks, a diminutive thing with turquoise underwings banded irregularly with red and white spots, manage, eons back in time, to chart a path across America, from Maine to Arizona, where it “seems to have found its true home”? “It is wonderful when we think of it,” he noted, “that a delicate butterfly, expanding scarcely more than one inch, should have found its way through a whole series of States, even into Canada.”41 Or how did caterpillars, riddled by parasitoids or nibbled to near death from within, find the energy to go on living? How did female butterflies know to deposit their eggs on the right larval food plants? Edwards wrote eloquently about this habit of the female, characteristic of all butterflies and moths:

  Nothing seems more wonderful than that the egg should invariably be laid on the food plant proper to its caterpillar; for very few caterp
illars are omnivorous, but nearly all will feed on two or three, and often on one species only of plant, and if they do not find the right plant they die of hunger. It would seem as if the butterfly has a remembrance of her former caterpillar state. Now she is as different as possible, a creature of the sun and air, eating no solid food, for she has no mouth, but lives on liquids drawn up through a tube; then she was a crawling worm, and voraciously fed on leaves, cutting them with powerful jaws. And between these stages there has intervened another that would have seemed to have divided them completely, certainly to have extinguished all recollections in the butterfly. And yet she seeks the particular plant her caterpillar must feed on, and finds it.42

  Grote thought it even more “wonderful” that moths found the right food plants, since they did all their searching “in the dark.”43

  Many butterflies managed to cope—even conquer—the nightmares nature dealt them. In every case, Scudder, Edwards, and Grote maintained that how these insects related or failed to relate to their complex environment made all the difference. Adaptive ability, in other words, sharpened and honed by chance (not by choice) over many, many years, sealed their fate. Scudder said sweepingly what the others also believed. “Observe,” he wrote in his excursus 64, “Postures at Rest and Asleep,” “how wonderfully alike are the actions of butterflies of the same group, i.e., descendants of the same stock; their habits have become ingrained by repetition through the ages; habits which it were almost certain destruction not to obey, since in nearly every one protective meaning may be found.”44 Every facet of a successful butterfly’s identity, from egg to metamorphosis and adulthood, was an outgrowth of the butterfly’s need to fight off assault.

  Some butterflies survived environmental dangers because they had acquired hibernating abilities. Others became multibrooded. Still others produced eggs and pupae sturdy enough to withstand even the most deadly winter sieges. Sometimes, as both Scudder and Grote showed, geological shifts carried butterflies off to new homes far from their origins, where they lodged themselves, such as the White Mountain butterfly, in New Hampshire. Other lepidoptera acquired another skill: they migrated when things got tough. Scudder wrote of sudden butterfly swarmings and sudden disappearances, and of interlopers descending from the north and invaders from the south, such as the giant swallowtail, an ordinarily southern species, “now established in the extreme southwestern corner” of New England, and the buckeye butterfly, with an apparent “tolerably secure foothold in southern Connecticut.”45 He recounted the life history of an “invasive” colonizer par excellence: the cabbage butterfly (Pieris rapae), a small white European pierid that, let loose on a grand scale, became a major agricultural pest, one of the few such in the butterfly world. Said to have been introduced into the United States from Quebec in 1860, it had spread southward to the gardens of New York City by the decade’s end. A keen-eyed Theodore Mead reported, “I myself found it swarming about parks in the heart of the city in June 1870.” By 1880, the European pierid had taken up residence nearly everywhere in North America, an achievement Scudder mapped from beginning to end in one of the first visual records ever conceived of such activity, using data from his many correspondents.46