How Not to Be Eaten. Dr. Gilbert Waldbauer

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How Not to Be Eaten - Dr. Gilbert Waldbauer

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caterpillars lived on sloths and that the caterpillars fed on the plentiful growth of green algae on the sloths' hair or ate the hair itself. But in 1976 Jeffrey Waage and G. Gene Montgomery reported that although they found many adult moths on sloths, they found no eggs, caterpillars, or pupae. But they did find caterpillars feeding on sloth dung. About once a week a sloth descends to the ground to defecate. Hanging from a vine, it scoops out a pit with the long, curved claws on its hind legs, deposits about a cupful of fecal pellets in the pit, and covers it with leaf litter. Female moths briefly leave the sloth to lay their eggs on its yet-to-be-covered dung. The caterpillars eat dung, and when the moths emerge from the pupae in the dung pit, they fly up into the trees to find a sloth. They mate on the sloth, and gravid females leave the animal only long enough to lay their eggs.

      Some insects construct their own hiding places. Working together, several hundred newly hatched tent caterpillars (Malacosoma americanum) of eastern North America spin a small tent of silk. As the caterpillars grow, they continuously enlarge the tent until it is about 2 feet long. Shaped like upside-down pyramids in the crotches of wild cherry trees, these tents are a common sight along country roads in spring. At night and during the cool parts of the day—early morning and late afternoon—the caterpillars shelter in the tent, where they are protected from many parasites and predators, Terrence Fitzgerald explained in The Tent Caterpillars. When it is warm enough, they leave the tent en masse and march nose to tail in single file to a leafy branch to feed, laying down a pheromone trail that will later guide them back to the nest.

      Groups of other insects, mainly caterpillars, also cooperate to spin the communal silken nests in which they live. The messy nests of the fall webworm (Hyphantria cunea), constructed on the leafy branches of many kinds of trees, are a common sight in late summer in much of southern Canada and the United States. In spring and early summer, the webworm moths emerge from silken cocoons hidden under leaf litter or a flake of bark and lay their eggs in clusters of several hundred on the undersides of leaves. Upon hatching, the caterpillars immediately begin, as Ephraim Felt explained, “to spin a communal web under which they feed. This protecting web is extended to include more and more foliage till finally a considerable portion of a branch may be enclosed.” The caterpillars partly skeletonize leaves, eating only the upper surface, leaving the veins and the lower surface intact. “The skeletonized leaves within the nest soon dry, turn brown, and they, with the frass [excrement] and cast skins of the caterpillars, render the nests very unsightly objects.”

      The caterpillars known as bagworms (family Psychidae) are well named. They live in cocoonlike pouches that they make of silk and decorate with bits of leaves and twigs. The head and thorax can be protruded through an opening in the bag, enabling the caterpillar to crawl and eat leaves. Fecal pellets are expelled through an opening at the other end of the bag. The familiar evergreen bagworm (Thyridopteryx ephemeraeformis) feeds mainly on junipers (red cedars) and arborvitae and, like other species of its family, spends virtually its entire life in its bag. The eggs laid by the wingless females overwinter in the bag. In spring, the newly hatched larvae leave the bag and immediately build their own bags, which they continually enlarge as they grow. In autumn, the fullgrown caterpillars pupate in their bags. The winged males emerge from the bags but, having vestigial mouthparts and unable to feed, live for only about a day. Drawn by a female's sex-attractant pheromone, a male thrusts his extensible abdomen far up into her bag and inseminates her. Only after laying their eggs do the larvalike adult females—which lack antennae, legs, and wings—emerge from the pupal skin, drop out of the bag, and die.

      A cocoon protects many insects, most famously moths, during the pupal stage, when they are especially vulnerable to predators because being virtually immobile, they cannot run away or defend themselves. Before molting to the pupal stage, Comstock noted, caterpillars “make provision for this helpless period by spinning a silken armor about their bodies.” As we will see in chapter 9, several of the giant silkworm moths (family Saturniidae) of North America spin very large tough-walled cocoons, in which they spend the winter in the pupal stage. The huge cecropia caterpillar, for example, constructs a double-walled cocoon 3 or more inches long and immovably attached along its length to a sturdy twig.

      In 1978, one of the two homes of the Green Revolution, the International Rice Research Institute (IRRI) on the island of Luzon in the Philippines, invited me to visit and develop a method for testing many thousands of rice varieties for resistance to the rice leaf folder, a moth of the family Pyralidae and an important rice pest. The main problem was figuring out a way to raise large numbers of leaf folder caterpillars in the laboratory so that the varietal tests could be done in a greenhouse. If the varieties to be tested are planted outdoors, the results of the test may be inconclusive, because as luck is likely to have it, the natural population of leaf folders will be too small or almost nonexistent that year.

      Gottfried Fraenkel, who years before had supervised my PhD research, was invited to do the very same thing with rice leaf folders by the Central Agriculture Research Institute of Sri Lanka. About six months after I arrived at IRRI, Gottfried stopped off to see me on his way to Sri Lanka. When he asked me if I had made any progress, I oneupped my former boss, handing him a copy of a manuscript ready for publication that described my then recently devised method for testing rice plants for resistance to the leaf folder.

      In Sri Lanka, Gottfried did other research projects with this insect, including a masterly study published in a Dutch journal in which he and Faheema Fallil wrote of the leaf folder, “Its characteristic behaviour is to spin a rice leaf longitudinally into a roll, by stitching together opposite rims of the leaf, and to feed inside this roll, leaving the epidermis on the outside of the roll intact,” as camouflage. Lying aligned with the long axis of the long, narrow leaf, the caterpillar swings the head end of its body from side to side in the same spot as many as one hundred times, forming a thick band of silk fibers that joins the edges of the leaf together. By repeating this procedure as it advances short distances along the leaf, the caterpillar forms as many as thirty such crossbands. “A newly woven band,” Fraenkel and Fallil found, “quickly becomes shorter by a process of contraction…bringing the rims of the leaf blade closer together…. With each succeeding band, this distance becomes shorter until the leaf is completely rolled up.”

      If an insect's lifestyle does not commit it to living under cover, in hiding—or if it lacks an effective physical or chemical defense—it will most likely have another way of protecting itself against predators. Some insects, as we will see in chapters 4 and 5, are camouflaged, blend in with the background, or resemble an inedible object, but generally speaking, most defenseless species flee to a hiding place when they feel threatened—even camouflaged individuals whose cover is blown.

      In 2008, Oswald Schmitz reported that red-legged grasshoppers (Melanoplus femurrubrum) respond differently to ambushing “sit and wait” spiders and to “roaming, actively hunting” spiders. Grasshoppers respond to sit and wait spiders, but not to roaming spiders, by shifting from their preferred food plant, a nutritious grass, to goldenrod, which is not a favorite food but on which they are less likely to be killed by a spider.

      Most cockroaches, as Thomas Eisner and his coauthors so aptly put it, “crave concealment. Anyone who has shared a kitchen with cockroaches knows that they seek shelter by day and that they are driven to flee for cover at night if a light is turned on.” This is the way of not only the tiny minority of cockroaches that have become household pests but also most of the world's almost four thousand other cockroach species, which live in natural settings.

      An insect that hides in a crevice or under a fallen leaf, a flake of bark, a rock, or a clod of soil would, ideally, have eyes not only on its head but also on its tail end so that it could tell if all of its body was safely tucked away in the dark of its hiding place. No insect or other arthropod has eyes on its tail end, but according to M. S. Bruno and D. Kennedy, a crayfish, a spiny lobster, and a shrimp have what Sir Vincent

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