Only in the 1600s did Dutch biologist Jan Swammerdam with his new invention, the microscope, demonstrate that the larva and the adult insect were one and the same individual throughout. The microscope enabled people to see that if a larva or pupa was cut open carefully, clearly recognisable 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 to 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 notes that a German scientist was charged with heresy in Chile as late as the 1830s because he could transform larvae into butterflies. Experts continue discussing the exact details of the metamorphosis process even now. Luckily, there are still some mysteries left in this world.
Insects don’t have lungs and don’t breathe through their mouths like 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 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 haemolymph – 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 colours our mammal blood red. Consequently, insect blood is colourless, yellow or green. That is why your car windscreen 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 is instead covered in yellowish-green splatters.
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, towards the head and the brain.
Insects’ sensory impressions are processed in the brain. It is tremendously important for them to pick up signals from their surroundings in the form of scent, sound and sight if they are to find food, avoid enemies and pick up partners. Although insects have the same basic senses as us humans – 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, unlike us, 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 kilometres away, even in extremely low concentrations.
In many ways, insects communicate through smell. Scent molecules allow them to send each other various kinds of messages, from 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 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’s 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 hermit beetle, one of Europe’s largest and rarest beetles, wooing a girlfriend in the neighbouring 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 drink.
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 forest and farmland. 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 realised 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 blow flies. 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 blow flies to come visiting, you need to yell at them in blow-fly 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 utterly irresistible if you happen to be a blow fly.
But you don’t have to visit 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 UK, 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 pull. So, what is a bewildered newly hatched male digger wasp to do, whose short life is dominated by but a single thought? 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. But what he doesn’t know is that during these ill-fated pairings, he has picked up some yellow structures that look a bit like ‘deely-boppers’ – popular party headwear if you remember the Eighties. These structures 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 hotting up. In this way, the existence of both the fly orchid and the digger wasp is assured.
Although communicating through scent is important for insects, especially when 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 this little