Insects have ears in all sorts of peculiar places but rarely on their heads. They may be on their legs, their wings, their thorax or their abdomen. Certain moths even have ears in their mouths! Insect ears come in a number of variants and even though all of them are XXXS size, some are incredibly intricate. One type has a vibrating membrane, like a tiny drum, whose skin is set in motion every time sound waves from the air reach it. It isn’t so unlike our own inner ear, just in a simplified miniature version.
Insects can also sense sound through different sensors connected to small hairs which pick up vibrations. Mosquitoes and fruit flies have these kinds of sensors on their antennae, while the bodies of butterfly larvae may be covered in sensory hairs which they use to hear, touch and taste. Some ears can pick up sounds a long way off, while others only operate over very short distances. It’s sometimes difficult to say what ‘hearing’ actually is: for example, are you hearing or feeling when you pick up vibrations in the stem of the stalk of grass you’re perched on?
If you are small, you can use an amplifier to boost your sound – like the insects commonly known as deathwatch beetles (Xestobium rufovillosum). In the olden days, people thought that the sound they made was a forewarning of imminent death, but the actual explanation is much more prosaic. These beetles live out their larval existence in rotting woodwork, often in the timbers of houses. As adults, the beetles find themselves partners simply by banging their heads against a wall. The sound transmits effectively through the woodwork and is picked up by both the beetles and us humans. This repetitive knocking is reminiscent of a ticking clock, or perhaps even more like somebody drumming their fingers impatiently on a table. According to ancient superstition these sounds meant somebody would die soon: they were a clock counting down a person’s final hours, or the Grim Reaper waiting restlessly. Most probably, the fact is that it was just easier for people to hear these sounds at night in a quiet house, when, say, they were keeping watch at somebody’s deathbed.
Fiddling on the World’s Tiniest Violin
There are other insect sounds that we hear distinctly even in the clear light of day, like the song of the cicadas. Even so, cicadas aren’t the winners in the competition for the world’s noisiest insect. Adjusted for size, an aquatic insect a mere 2 millimetres long is the one most likely to walk away with the prize. Because the male of the water boatman species, part of the Micronectidae family, competes for the females’ attention by making music. But how are you supposed to serenade your sweetheart when you’re the size of a coarse-ground peppercorn? Well, the little water boatman does it by playing himself, using his abdomen as a string and his penis as a bow.
A couple of years ago, a team of scientists set up underwater microphones to record the song of French male water boatmen – the first-ever bootleg recording of this serenade. And what a hit it was, in its way! The scientists believed they could prove that these tiny creatures with their fiddling penises exceeded all bounds of reason when it came to sound production. An average sound level of no less than 79 decibels made by a critter a mere 2 millimetres in length: on land that’s equivalent to the sound of a freight train passing by at a distance of around 50 feet.
It seems almost beyond the realms of possibility, and it may actually not be true either, because it’s a complicated business comparing sounds underwater and in the air. Perhaps the water boatman will turn out not to be the world’s noisiest insect after all. But the fact that it fiddles with its own penis – well, you can’t take that away from it.
Tongues Beneath their Feet
Imagine if you could walk barefoot through the forest in summertime and actually taste the blueberries in the bushes as you stepped on them. This is what houseflies do – they taste with their feet. And flies are unbelievably hypersensitive, apparently a hundred times more sensitive to sugar than we are with our tongues.
But there are a few disadvantages to being a fly, on top of being a mostly unwanted creature to begin with. They don’t have teeth or any other equipment that would enable them to eat solid food, which dooms them to an eternally liquid diet. So what is a poor housefly to do when it lands on something tasty, like your slice of bread? Well, it uses digestive enzymes from its belly to turn the food into a smoothie. To do so, the fly has to regurgitate some of its gastric juices onto the food, which isn’t so great for us humans because it means that bacteria from the fly’s last meal – possibly far from anything we’d classify as food – may end up on our slice of bread. But it’s great for the fly, who can now suck up the food. The housefly’s mouth is like a spongy vacuum cleaner head on a short shaft. The whole thing is attached to a kind of pump in the head, which creates suction, allowing the fly to hoover up the yummy nutritious soup.
Houseflies’ poor table manners and somewhat varied diet, which includes items such as animal dung, are the reasons why they spread infection. The flies aren’t dangerous in themselves, but like used syringes, they can carry infections and pass them on to us.
And now I think about it, maybe it’s just as well we humans taste with our tongue and not our feet. Blueberry shrubs are one thing, but the thought of going around tasting the insides of your shoes all winter long is hardly appealing.
Insects’ senses are adapted to their environment and needs. Whereas dragonflies and flies need good vision, cave-dwelling insects may be totally blind. Insects that come into close contact with flowers, like honeybees, can also see colours, but their colour spectrum is shifted upwards so that they don’t see red light. On the other hand, they can see ultraviolet light, unlike us humans. This means that many flowers we see as monotone, such as sunflowers, have distinctive patterns for a bee, often in the form of ‘landing strips’ that direct them towards the source of nectar in the flower.
Insects’ compound eyes consist of many individual eyes. The brain merges all the tiny pictures together into a single large image, although it is coarser and fuzzier than the way we humans see the world (it looks a bit like a low-res photograph on your PC screen when you’ve zoomed in too close). There are plenty of reasons why insects don’t have driving licences, of course, but sight is a big one: they would never be able to read a road sign at 20 metres as the image would be too blurry. That said, their vision is supremely adapted to the tasks that will fill their days. Take whirligig beetles, for example: shiny black pearls of beetles that dash around on the surface of the waters of our lakes. They have two pairs of eyes, with different refraction: one pair for seeing clearly underwater so that they can watch out for hungry perch, and another for seeing clearly above the water so that they can find food on the surface.
Insects can also see a property to which we humans are blind: polarised light. This has to do with which plane the light is oscillating in, and it alters when sunlight is reflected – in the atmosphere or on a shining surface like water. But let’s go easy on the physics and restrict ourselves to saying that insects use polarised light as a compass that enables them to orientate themselves. We humans only relate to polarised light when we put on a pair of Polaroid sunglasses to reduce the glare of reflected light.
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