giving insects undreamed-of opportunities to flaunt their best features in new, sky-high pick-up joints.
We don’t know exactly when wings first developed. Perhaps they evolved from outgrowths on the thoracic area; outgrowths that may have served as solar collectors or a means of stabilising the body after a jump or a fall. Perhaps the wings evolved from gills. Regardless, the most important point here is that insects discovered that these gadgets of theirs were also brilliant for gliding down from trees or high plants. Insects with well-developed wing nubs got more food, lived longer and – as a result – had more offspring, which, in turn, inherited these super wing nubs. In this way, evolution ensured that wings became commonplace, and at a pretty rapid rate, too, in the context of geological timescales. Soon the air was alive with all manner of shimmering, whirring wings.
One point is crucial to understanding how wildly successful wings were for the early insects: nobody else could fly! There were not yet any birds, bats or pterosaurs, and they would be a long time coming. This meant that insects had global dominance of the air for more than 150 million years. In comparison, our own species, Homo sapiens, has spent a total of just 200,000 short years on the planet.
Insects have survived five rounds of mass extinction. The dinosaurs first staggered out into the world after the third of these, around 240 million years ago. So next time you catch yourself thinking how irritating an insect is, bear in mind that this animal class has been on the planet since long before the dinosaurs. That alone merits a little respect, if you ask me.
Small Creatures, Smart Design: Insect Anatomy
So how are they put together, these tiny creatures with whom we share our planet? The following section is a crash course in insect construction. It also shows that, despite their modest size, insects can count, teach and recognise both each other and us humans.
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 mid-section of their body.
The next step is to check whether the bug has wings. These are also on the mid-section. Most insects have two pairs of wings: forewings and hindwings.
You have now indirectly grasped one crucial hallmark of insects: their bodies are divided into three. As one of many representatives of the phylum Arthropoda, 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 animal 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. While insects never have more than two antennae, their eyes can vary in number and type. And just so you know: insects don’t necessarily only have eyes on their head. One species of swallowtail butterfly 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 she is laying her eggs in the right place.
If the head is the insect’s sensory centre, the mid-section – the thorax – is the transport centre. This segment is dominated by the muscles needed to power the wings and legs. It is worth noting that, unlike all other creatures that can fly or glide – birds, bats, flying squirrels, flying fish – insect 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 completely closed structure the 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 flat without a toilet, they have no choice but to hold it in. Only once the larval stage is complete are the gut and the gut opening connected. See also Chapter 7, here.
Living in an Invertebrate World
Insects are invertebrates – in other words, animals without a backbone, skeleton or bones. Instead, 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 onto 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 and 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 armour, expanding and rising until it has nowhere left to go. But insects have a solution: new armour, soft to start with, forms beneath the old. The old, rigid armour cracks open and the insect jumps out of its skin as casually as we’d shrug off a well-worn shirt. Now it’s crucial for the insect to literally inflate itself to make the new, soft armour as big as possible before it dries and hardens. Because once the new exoskeleton has hardened, the insect’s potential for growth is determined until another moulting 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 moulting process only occurs in insects’ early lives.
Time of Transformation
Insects come in two variants: those that change gradually through a series of moultings and those that undergo an abrupt change in the process of developing from child to adult. This transformation is called a metamorphosis.
The first type – e.g. dragonflies, grasshoppers, cockroaches and true bugs (see also here) – 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 flourish. For these insects, the childhood stage is known as the nymph stage. The nymphs grow, cast off their exoskeleton a few times (just how many times varies by species, but often three to eight times) and become increasingly like the adult versions. Then, finally, the nymph moults 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
