Extraordinary Insects

The Fabulous, Indispensable Creatures Who Run Our World

Anne Sverdrup-Thygeson

• Publisher: Simon & Schuster
• Year: 2019
• ISBN:
  9781982112899
• Topic: Biowissenschaften
• Subtopic: Entomologie

This enthusiastic, witty, and informative introduction to the world of insects and why we could not survive without them is "a joy" ( The Times, London) and "charming...Highlighting them in all their buzzing, stinging, biting glory" ( The New York Times Book Review ). Insects comprise roughly half of the animal kingdom. They live everywhere — deep inside caves, 18, 000 feet high in the Himalayas, inside computers, in Yellowstone's hot springs, and in the ears and nostrils of much larger creatures. There are insects that have ears on their knees, eyes on their penises, and tongues under their feet. Most of us think life would be better without bugs. In fact, life would be impossible without them.Most of us know that we would not have honey without honeybees, but without the pinhead-sized chocolate midge, cocoa flowers would not pollinate. No cocoa, no chocolate. The ink that was used to write the Declaration of Independence was derived from galls on oak trees, which are induced by a small wasp. The fruit fly was essential to medical and biological research experiments that resulted in six Nobel prizes. Blowfly larva can clean difficult wounds; flour beetle larva can digest plastic; several species of insects have been essential to the development of antibiotics. Insects turn dead plants and animals into soil. They pollinate flowers, including crops that we depend on. They provide food for other animals, such as birds and bats. They control organisms that are harmful to humans. Life as we know it depends on these small creatures."Delivering a hail of facts with brio and precision" ( Nature ) Anne Sverdrup-Thygeson shows us that there is more variety among insects than we thought possible and the more you learn about insects, the more fascinating they become. Extraordinary Insects is "a very enthusiastic look at the flying, crawling, stinging bug universe world, and why we should cherish it" ( The Philadelphia Inquirer ).**Note: This book was previously published under the title Buzz, Sting, Bite.

1

Small Creatures, Smart Design

---

Insect Anatomy

So how are they put together, these tiny creatures we share the planet with? The following section is a crash course in insect construction. It also shows that, despite their modest size, insects can count, teach, and recognize both one another and us.

Six Legs, Four Wings, Two Antennae

What exactly is an insect? If you’re in any doubt, a good rule of thumb is to start by counting legs—because most insects have six legs, all attached to the midsection of their body.

The next step is to check whether the bug has wings. These are also on the midsection. Most insects have two pairs of wings: forewings and hind wings. You have now indirectly grasped one crucial hallmark of insects: their bodies are divided into three parts. As one of many representatives of the Euarthropoda phylum, insects are formed of many segments, although in their case, these have merged into three pretty clear and distinct sections: head, thorax, and abdomen.

The old segments still appear as indentations or marks on the surface of many insects, as if somebody had cut them with a sharp implement—and in fact, that is what gave this class of animals its name: the word insect comes from the Latin verb insecare, meaning “to cut into.”

The front segment, the head, isn’t so unlike our own: it has both a mouth and the most important sense organs—eyes and antennae. Though insects never have more than two antennae, their eyes can vary in number and type. And just so you know: insects don’t necessarily have eyes just on their head. One species of swallowtail butterflies has eyes on its penis! These help the male to position himself correctly during mating. The female also has eyes on her rear end, which she uses to check that she is laying her eggs in the right place.

If the head is the insects’ sensory center, the midsection—the thorax—is the transport center. This segment is dominated by the muscles needed to power the wings and legs. It is worth noting that, unlike those of all other animals that can fly or glide—birds, bats, flying squirrels, flying fish—insects’ wings are not repurposed arms or legs but separate motor devices that supplement the legs.

The abdomen, which is often the largest segment, is responsible for reproduction and also contains most of the insect’s gut system. Gut waste is excreted at the rear. Usually. The minute gall wasp larvae, which live out their larval existence in the gall a plant builds around them, are extremely well brought up. They know it’s wrong to foul your own nest, and since they are trapped in a one-room apartment without a toilet, they have no choice but to hold it in. Only after the larval stage is complete are the gut and the gut opening connected.

Living in an Invertebrate World

Insects are invertebrates—in other words, animals without a backbone, skeleton, or other bones. Their “skeleton” is on the outside: a hard yet light exoskeleton protects the soft interior against collision and other external stresses. The outermost surface is covered in a layer of wax, which offers protection against every insect’s greatest fear: dehydration. Despite their small size, insects have a large surface area relative to their tiny volume, meaning that they are at high risk of losing precious water molecules through evaporation, which would leave them as dead as dried fish. The wax layer is a crucial means of hanging on to every molecule of moisture.

The same material that forms the skeleton around the body also protects the legs and wings. The legs are strong, hollow tubes with a number of joints that enable the insect to run, jump, and do other fun things.

But there are a few disadvantages to having your skeleton on the outside. How are you supposed to grow and expand if you’re shut in like this? Imagine bread dough encased in medieval armor, expanding and rising until it has nowhere left to go. But insects have a solution: new armor, soft to start with, forms beneath the old. The old, rigid armor cracks open, and the insect jumps out of its skin as casually as we’d shrug off a shirt. Now it’s crucial that it literally inflate itself to make the new, soft armor as big as possible before it dries and hardens. Because once the new exoskeleton has hardened, the insect’s potential for growth is fixed until another molting paves the way for new opportunities.

If you think this sounds tiring, it may be a consolation to hear that (with a few exceptions) the lengthy molting process occurs only in insects’ early lives.

A Time of Transformation

Insects come in two variants: those that change gradually through a series of moltings and those that undergo an abrupt change in the process of developing from child to adult. These transformations are called metamorphosis.

The first type—e.g., dragonflies, grasshoppers, cockroaches, and true bugs (the order Hemiptera)—gradually change in appearance as they grow, a bit like us humans, except that we don’t have to shed our entire skin in order to grow. For these insects, the childhood stage is known as the nymph stage. The nymph grows, casts off its exoskeleton a few times (just how many varies by species, but often three to eight times), and becomes increasingly like the adult version. Then, finally, the nymph molts one last time and crawls out of its used larval skin equipped with functioning wings and sex organs. Voilà! It has become an adult!

Other insects undergo a complete metamorphosis—an almost magical change in appearance from child to adult. In our human world, we have to turn to fairy tales and fantasy for examples of this sort of shape-shifting, such as kissed frogs turning into princes or Minerva McGonagall shape-shifting into a cat. But for insects, kissing and spells aren’t the cause of the change. The metamorphosis is driven by hormones and marks the transition from child to adult. First the egg hatches into a larva that looks nothing like the creature it will ultimately become. The larva often looks like a dull, pale, rectangular bag, with a mouth at one end and an anus at the other (although there are some exceptions, including many butterflies). The larva molts several times, growing bigger on each occasion but otherwise looking pretty much unchanged.

The magic happens in the pupal stage—a period of rest in which the insect undergoes the miraculous change from anonymous “bag creature” to an incredibly complicated, ingeniously constructed adult individual. Inside the pupal case, the whole insect is rebuilt, like a Lego model whose blocks are pulled apart and put back together again to make an entirely different shape. In the end, the pupa splits and out climbs “a beautiful butterfly”—as described in one of my all-time favorite children’s books, The Very Hungry Caterpillar. Total transformation is brilliant and undoubtedly the most successful variant. Most insect species on the planet, 85 percent of them, undergo this type of complete metamorphosis. This includes the dominant insect groups, such as beetles, wasps and their relatives, butterflies and moths, and flies and mosquitoes.

The ingenious part is that they can exploit two different diets and habitats as child and adult, concentrating on their central task in each phase of their lives. The earthbound larvae, whose focal point is energy storage, can be eating machines. Then, in the pupal stage, the accumulated energy is melted down and reinvested in a new organism: a flying creature dedicated to reproduction.

The connection between larvae and adult insects has been known since ancient Egyptian times, but people didn’t understand what was happening. Some thought that the larva was a stray fetus that eventually came to its senses and crawled back into its egg—in the form of the pupa—in order to be born at last. Others claimed that two totally different individuals were involved, the first of which died and was then resurrected in a new form.

Only in the 1600s did Jan Swammerdam and his microscope demonstrate that the larva and the adult insect were the same individual throughout. The microscope enabled people to see that if a larva or pupa was carefully cut open, clearly recognizable elements of the grown insect could be found beneath the surface. Swammerdam enjoyed displaying his skills with scalpel and microscope before an audience and used to demonstrate how he could remove the skin from a big silkworm larva and reveal the wing structure beneath, complete with the characteristic veined patterning on the wings.

Even so, this did not become general knowledge until much, much later. In his journal, Charles Darwin noted that a German scientist was charged with heresy in Chile as late as the 1830s because he could transform larvae into butterflies. Experts still discuss the exact details of the metamorphosis process even now. Luckily, there are still some mysteries left in the world!

Breathing through a Drinking Straw

Insects don’t have lungs and don’t breathe through their mouths as we do. Instead, they breathe through holes in the sides of their bodies. The holes run, like drinking straws, from the surface of the insect into its interior, branching out along the way. Air fills the straws, and the oxygen then passes out of them and into the body’s cells. This means that the insects don’t need to use their blood to transport oxygen to the various nooks and crannies of their bodies. However, they do still need some kind of blood—known as hemolymph—to carry nutrition and hormones to the cells and to clear them of waste material. Since insect blood doesn’t transport oxygen, there is no need for the ferrous red substance that colors our mammal blood red. Consequently, insect blood is colorless, yellow, or green. That is why your car windshield doesn’t end up looking like a scene from a bad crime novel when you’re driving along on a hot, still summer afternoon but ends up covered in yellowish green splatters instead.

Insects don’t even have veins and arteries: instead, insect blood sloshes around freely among the bodily organs, down into the legs, and out into the wings. To ensure a bit of circulation, there is a heart of sorts: a long dorsal tube with muscles and openings on the side and at the front. Muscle contractions pump the blood forward from the rear, toward the head and brain.

Insects’ sensory impressions are processed in the brain. It is tremendously important for them to pick up signals from their surroundings in the forms of scent, sound, and sight if they are to find food, avoid enemies, and pick up mates. Although insects have the same basic senses as we do—they sense light, sound, and smell and can taste and feel—most of their sense organs are constructed in a totally different way. Let’s take a look at insects’ sensory apparatus.

The Fragrant Language of Insects

The sense of smell is important for many insects, although they lack a nose, doing most of their smelling through their antennae instead. Some insects, including certain male moths, have large, feathery antennae that can pick up the scent of a female several miles away even in extremely low concentrations.

In many ways, insects speak through smell. Scent molecules allow them to send each other various kinds of messages, from soppy personal ads such as “Lonesome lady seeks handsome fella for good times” to ant restaurant recommendations: “Follow this scent trail to a delicious dollop of jam on the kitchen counter.”

Spruce bark beetles, for example, don’t need Snapchat or Messenger to tell each other where the party is. When they discover an ailing spruce tree, they shout about it in the language of scent. This enables them to gather together enough beetles to overpower a sickly living tree—which then ends its days as a kindergarten for thousands of beetle babies.

We miss out on most of these insect scents, which we simply can’t smell. But if you wander beneath the greenery of ancient trees on a late-summer day in the town of Tønsberg, southern Norway, you may be lucky enough to pick up the most delightful aroma of peaches: it is the scent of the hermit beetle, one of Europe’s largest and rarest beetles, wooing a girlfriend in the neighboring tree. The substance it uses rejoices in the thoroughly unromantic name of gamma-decalactone, and we humans produce it in labs for use in cosmetics and to add aroma to food and drinks.

The scent is very helpful to the hermit beetle, which is heavy and sluggish and seldom flies, or not far at any rate. It lives in ancient hollow trees, where its larvae gnaw on rotted wood debris, and it’s a real homebody: a Swedish study found that most adult hermit beetles were still living in the same tree they were born in. This lack of interest in travel complicates the business of finding new hollow trees to move into, and the situation is hardly helped by the fact that old, hollow trees are an unusual phenomenon in today’s intensively exploited forests and farmlands. As a result, the species, which is scattered across western Europe from southern Sweden to northern Spain (though not the British Isles), is decreasing all over its range and is protected in many European countries. In Norway, it is considered critically endangered and can be found in only one place: an old churchyard in Tønsberg. Or two places, to be precise, because some individuals have recently been moved to a nearby oak grove in an effort to secure the survival of the species.

Flowery Temptresses

Flowers have realized that scent is important to insects—or rather, millions of years of mutual evolution have resulted in the most incredible interactions. The world’s largest flower, which belongs to the Rafflesia genus and is found in Southeast Asia, is pollinated by blowflies. This means that “a scent of warm summer sun meets a cool evening breeze with a hint of amber and sensual vanilla”—to borrow perfume industry terminology—isn’t going to cut the mustard. No, indeed. If you want blowflies to come visiting, you need to yell at them in blowfly language. That is why the world’s biggest flower smells like a dead animal whose carcass has been lying around in the heat of the jungle a couple of days too many—a stench of rotting flesh that is irresistible if you happen to be a blowfly.

But you don’t have to go the jungle to find examples of flowers that speak the insects’ language of scent. The fly orchid is a protected native European species, rare in Norway and the United Kingdom but widespread throughout central Europe. It has strange brownish blue flowers that look just like the female of a certain digger wasp species. And its beautiful appearance is supplemented by the right scent: the flower smells identical to a female digger wasp on the prowl. So what is a bewildered newly hatched male digger wasp, whose short life is dominated by a single thought, to do? He falls for the trick and tries to mate with the flower. When things don’t go so well, he moves on to what he thinks is the next female and tries again. No luck there, either. What he doesn’t know is that during these ill-fated pairings, he has picked up some yellow structures that contain the fly orchid’s pollen, so the male digger wasp’s feverish flirting contributes to the flowers’ pollination.

And if you’re concerned about the fate of the unfortunate male, please don’t despair. The real females hatch a few days after the males, and then things really start heating up. In this way, the existence of both the fly orchid and the digger wasp is ensured.

Ears on Their Knees and Deathwatch Beetles

Although communicating through scent is important for insects, especially if they’re searching for a mate, some rely on sound to find a partner instead. The grasshopper’s song is not designed to create the sound of summer for us humans but to find a girlfriend for the little green creature; it is usually the male calling out to the female, in the same way as male birds are frequently the keenest warblers. If you’ve heard the deafening wall of sound cicadas create in southern climes, bear in mind that it would be twice as loud if the ladies joined in. But as an ancient Greek saying has it, “Blessed are the cicadas, for they have voiceless wives.” Controversial as we may find this statement in modern society, let me just add that it may be pretty smart of the females to keep...