It is night and the owl stares steeply ahead. Its eyes are large, so large that the iris and pupil completely fill the eyeball. If it wants to look the other way, it has to turn its head. She cannot catch the scene with her eyes, either on the right or on the left, but she can easily turn her head 180 degrees on her long flexible neck, which even a long-tailed giraffe cannot do. The owl’s eyes are adapted to its needs, just as the eyes of other animals have adapted to their limited intelligence and requirements. Primitive ones do not have them, but just as a blind man can sometimes detect the difference between day and night with his light-sensitive nerves, so some animals can “see” light even though they have no sight. For example, the earthworm.
At night, it crawls to the dewy surface to nibble and breed, but if we shine white light on the lawn, it immediately retreats underground. It senses light with its skin but is colour blind. Red light does not move it anywhere, so fishermen can easily pick up earthworms if they shade their lamps with a red shade and walk as softly as possible.
The white sea raven uses its eyes to face the world. He is always up to date with what is happening around him and in nearby nests about 10 metres away, as he has to be because they are often hostile. It can look 180 degrees around from the nest because it has side vision, but it does not use it when hunting.
It sees well, but not as well as an eagle, which can detect the movement of a hair a kilometre and a half away with at least the same resolution as a human with binoculars magnified eight times. The hawk is not bad either, and its target has to move if it wants to see it. When it disappears on the horizon, it sees its keeper only if the keeper is moving, and the keeper does not see it even accidentally. Human eyesight is too weak to see it, but a small bird can. If a keeper loses his falcon but has a cage with the bird, he only has to take off the cover so that the bird can see the sky, and he has to turn his head in the direction of the invisible falcon.
Vultures also have good distance vision. They can spot even the smallest birds miles away in the sky, while they spend most of their waking hours in the heights, two or three kilometres away from each other. They are always looking around, for other vultures and for food. When one of them spots carrion or offal, it descends swiftly towards it. The nearest vulture notices this and immediately follows. His example is followed by his nearest neighbour, and his example again by the next neighbour, until all the vultures that had previously been sailing in the sky, some 150 kilometres across, are gathered for a feast. They are as picky as humans: they never touch plant food.
Blind seal
Seals also use eyesight for foraging. Their large eyes are adapted for underwater vision, but they can also catch prey when they can hardly see it, such as in murky sea shells. Even blind seals can survive.
A grey seal from the rocky island of Orkneys saw nothing, but successfully found enough food in the sea for herself and the pup she was carrying. When it was time to pup, she climbed 15 metres up the rocky terrain, gave birth and spent the next three weeks protecting her pup from her enemies. Then she returned to the sea.
She replaced her lost sight by touching her fins and whiskers, and most likely also relied on her memory. For seals, sight is extremely important, especially in the first year of life, when they are still free to roam around and explore the depths of the sea. After that, they attach themselves to a territory where they have discovered enough food and live there. Because the grey seal was probably not born blind, but went blind slowly, it had enough time to remember the surface of the island to which it returned each year and the patch of sea in which it foraged for food.
She was not the only one on Orkney to lose her sight. The land on which the pups spent the first three weeks of their lives was contaminated with seabird and seal droppings. As they rolled around on the ground, the little seals got some of the dirt in their eyes and, incidentally, they also got infected through wounds they sustained on sharp rocks or from the sharp teeth of their little companions. The infection slowly caused them to go blind, but before the darkness overwhelmed them, they knew the surface of the island and the sea well enough to survive.
Cancers do not have problems with conjunctivitis. The eyes have long movable tubes at the end of the eye sockets and absorb light through them. This affects their pigment cells, opening or closing them and changing their colour.
Fiddler’s cancer, for example, has pigmented cells all over the body and legs. At night it turns off-white and is lightest at low tide, during the day it is brownish-grey and darkest at low tide. In this way it deceives its enemies: if it were white during the day in shallow waters, its prey would avoid it at a distance, just as if it were dark at night in deep waters it would be suspicious. He would remain hungry.
When it was transferred from America to Europe, it changed colour in the dark aquarium at the same time of day as it did at home, but it adapted to the tidal and solar cycles of its new home as soon as it was released into the light. If he had eyes. When they were removed, he could no longer do this, because he apparently controls his internal rhythm by means of his eyes and his nerve ganglia. Then they cut off his leg. Before it died in the sunlight, the severed leg continued to change colour for a day or two, but according to the tides of the old home, not the new one, although the living body of this cancer adapts to the new rhythm as soon as it is exposed to daylight.
Frogs and toads have also had their eyes surgically removed. In fact, their brains were cut out and their limbs were cut off. They found that the severed limb continues to respond to stimuli for several hours, but without the eyes and brain, the frog lives for several days. But there is one problem: it can no longer eat. Its very large and bulging eyes are unusually adapted: it closes its eyelids and sticks the eyeball in its mouth to show food the way through its mouth when it is swallowing. Without the eyes, there is no signpost for food.
Frogs are also completely dependent on sight to hunt, yet blind frogs respond to light as if they could see. When a blind frog was placed in a closed box and its back was turned towards an opening through which light was coming, it immediately turned towards the light, even though there were no air currents in the box to guide it. The blind frog can still “see” with its skin, which is sensitive to light.
Even the lizard that was deliberately deprived of its eyesight still found its way to its home pool, even if it was released about a kilometre and a half away, but otherwise it is able to return to its home pool from a much greater distance. In one experiment, more than 1 000 lizards were tagged and taken to a neighbouring valley, some five kilometres away from the home pool and separated by hills. To return home, the lizards had to cross a completely unfamiliar area, climb a hill and probably walk 10 kilometres or more in search of a route. In the third year, 18 of them had still returned “home”.
Nothing similar has been done with snakes, and their vision has not been specifically tested. They are nearsighted and deaf, but this does not hinder their hunting because they compensate for the deficit by being extremely sensitive to vibrations. These vibrations travel through the skin to the bones, especially to the lower jaw and to the degenerated inner ear bone, because they do not have inner ears either. Snakes can thus ‘hear’ vibrations when the ground rumbles beneath them and can detect the movement of humans or animals at a distance, even mice in nearby grass. They are even more susceptible to vibrations in water because they are more easily transmitted through water.
In addition to vibrations, snakes also have a very acute sense of smell to help them perceive their surroundings. Strong scents, such as those emitted by humans, ferrets, golden martens, weasels, hedgehogs and other enemies, repel them strongly. They also prefer to avoid clothing and anything with humans on it. A snake will never willingly crawl into a human bed. If it does, as the stories say, it is only by accident, having fallen through a hole while hunting a mouse or a rat. Even the dreaded rattlesnake will not crawl over a rope that smells of human sweat without a great deal of urge.
Man is not the first choice for a meal for a snake, which detects its prey by the sense of smell at the tip of its tongue. It intercepts molecules floating in the air, because every smell, from food to living animals to the dead, is made up of molecules invisible to the eye, which travel through the air, the water or remain on the ground. The snake only uses its myopic eyes to intercept the molecules, analyse them and identify its prey. It looks towards the snake and attacks it.
Cavefish are caught with their “invisible eye”. They have a special organ between the nostril and the eye that can detect changes in temperature and detect infrared light at a short distance. So the hungry cave shrew crawls around, moving its head like radar to pick up even the slightest change in temperature. When it does, it slowly heads off in the direction dictated by the increasingly powerful infrared light until it finds its rat, mouse, bird, nest of eggs or something else that emits powerful energy in the form of waves.
Snakes can’t see clearly at night, but pit vipers can hunt on peacefully because receptors in the temperature organ inform them of the size and location of the infrared emitter, and their sense of smell tells them what kind of prey it is. Because they have one temperature-sensing organ under each eye, they can also calculate how long it will take them to reach their prey and how much time they have to prepare their bodies for an attack.
Mosquitoes are also very sensitive to heat. Males feed on flower nectar, and females generally eat this too, but if a female wants to hatch all the eggs she can, she needs to fortify herself with the blood of her chosen victim to get the much-needed proteins. Thus, one type of female seeks out deer, another some other animal, but all are led to their victims by the heat they give off. However, since the female’s life is short and a suitable victim is not always at hand, she makes do in an emergency with whatever blood is available, such as human or bovine blood. In a pinch, she may also break down her own small protein reserves, but in this case she will only lay enough eggs to keep the species going.
The female detects her prey with her two tentacles, which are only a few millimetres long. She wings them through the air until she detects the source of the infrared light with both of them. At that point, it automatically turns in the right direction, even if it is more than ten metres away from its warm-blooded meal, and flies straight towards it. It seems to prefer to attack people with sensitive skin, and this is also true of fleas. They also “watch” by sensing heat, so they may have just hatched and may already be jumping on their future host.
The smell of ants
Ants don’t jump, they walk or fly, aided by eyes like those of bees, butterflies, flies, wasps and many other insects. They can detect polarised light, which the human eye cannot because it is not made up of thousands of tiny layers, each of which acts like an independent eye.
Italian researcher Sanschi built a high fence around the North American ants and shaded them with a panel that didn’t let in light, so they couldn’t see the position of the sun or their way home. The ants still found it. He concluded that they could see the stars and orient themselves by them even in the daytime, although it was more likely that the polarised light from the sky, detected by their multifaceted eyes, showed them the way.
Worker ants can’t fly, so they can’t go very far to find food, but when they do, they pass the news on immediately. How? By moving and touching their extremely sensitive tentacles and hairs, and by smelling the food on their skin. For ants, touching is not just touching – at least they exchange information about the smell and taste of food, for example, if they don’t tell each other anything else.
When an ant finds food that its companions don’t yet know about, it eats as much as it can. Then it rushes home, but it marks the path from the food to the anthill in a generous manner. Every now and then, it squats and drops a tiny bit of its excrement on the ground. If the path is on a shiny surface, such as glass, it can be seen with the naked eye.
In the anthill, her fellow ants taste the food she has brought with their tentacles and this spurs them into action. They set off immediately. The smell of the droppings left behind by the ant that first brought the food leads them to the food, and now they mark the path in the same way to reinforce the trail. The smell of the trail remains strong as long as they still have something to take away, but when the food runs out, they abandon the trail and the smell slowly fades.
Smell is extremely important to them. If a person smudges their path at a certain point with his or her finger, which has a strong smell, the ants become momentarily confused and stop. They only resume their journey when one of them takes courage, crosses the obstacle and covers it with its scent. Two-way traffic is restored.
But an ant will stand still like a stopped clock if it is placed in a container that does not let in light. Without the vibrations of polarised light to carry messages to its brain and the encouragement of its squealing companions, it loses all sense of time, but when it returns to sunlight, it resumes where it left off.
Polarised light doesn’t help those ants that are more or less blind, but they too are on the march across the Earth’s surface. Outdoors, they orient themselves with very sensitive feelers and a keen sense of smell. They use their tentacles to wing through the air and catch food scent molecules. When they discover a meal, they first touch it with their tentacles and gently examine it. This allows them to detect the chemical structure of the food before they taste it, and to estimate its size or shape.
In the darkness of the anthill, all ants are blind, but they move through it with all certainty. This is made possible by their tentacles, smell and muscle memory. Both seeing and blind ants can also judge which food is edible and which is not. The hairs, which are sensitive to the chemicals on their tentacles, are connected to the brain. For example, when they detect fat on an insect’s tail, the brain tells them that the tail is inedible and so they don’t touch it, but if they detect edible chemicals with their tentacles, they bite down on the tail so quickly that the insect doesn’t have time to move it.
Central America is home to some very special blind ants. Organised like an army, they are nomads who set up anthills just long enough for the eggs to hatch and the larvae to pupate. At all other times they march around in wave-like columns. At their head are warriors who attack anything edible that comes in their path.
The leading group of warriors moves boldly forward, but only covers a short distance. Then it quickly rejoins the column, as if afraid that it has strayed too far from the familiar. A new group sets off. It follows the path marked by the scent of the first group and penetrates a little further. Then it too returns, and a third group sets off along the path marked by the first two, again conquering some new territory.
But sometimes they don’t. They follow the trail of other ants or their old trail, which still has a scent. The molecules of the excrement can persist for weeks or even months, making them an important means of communication, especially for animals that live in dispersal. When ants follow a familiar scent, they feel more at home, so they advance much faster and with more certainty.
They bivouac at night. They huddle close together and place the queen and the larvae in the centre of their living sphere, which they carry around to protect and keep warm. In the morning, the scouting parties set off first in tight columns, followed by the workers and foragers who look after the helpless larvae.
Ants seem to be pretty smart in their own right. Some species have turned leaf aphids, which feed on plant sap, into their own milking cows. They regularly tap them on their bellies with their tentacles to extract amber-coloured droplets of milk from the tentacles they have on them. In summer, when the aphids feed outdoors and eat a variety of vegetation, the ants graze them in the same way as humans graze cows. They move them to fresh pasture, only they do not drive them as man does cows, but carry them one by one in their shepherd’s jaws.
Some species put them in a safe and warm place before winter. They take them underground, in or near the anthill, to ensure that they can continue to get milk in the winter, when the aphids feed on the roots.
Other ant species “plant” their own mushrooms. They cut large circles out of the leaves, chew the leaves and cover their underground hotbeds with the material like fertiliser. There they ‘plant’ mushrooms and feed on their soft parts.
Even more cunning is the founder of a new colony of ants that feed on mushrooms. When she flies off on her honeymoon in spring, she takes her dowry from the anthill: a piece of mushroom end. On a calm sunny day, when thousands of other ants of both sexes are already in the air, she mixes herself in with them with this decisive proof that mushrooms will grow in her new anthill. She flies around, showing off her dowry, waiting to be fertilised by a tiny male.
When it has done its job, it exhales almost immediately, and the founder of the new colony drops to the ground and, with her sharp legs, cuts her wings with determination. Without them, she starts running and searching for a suitable hole in which to set up her anthill. There she hatches her first eggs to ensure that she has ants to feed her and make a warm house. In them will grow mushrooms, for which she herself has contributed the end of the anthill, which she has been carefully guarding all this time.
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Dance of the Eights
Bees rely on their eyesight to find food. Even though they can only distinguish four basic colours – yellow, blue-green, blue-violet and ultraviolet – they also descend on red flowers such as poppies, as they emit ultraviolet light. They prefer flowers with contrasting stripes to monochrome flowers because these lead them to nectar.
Beekeepers always know that colour is very important to bees, so they colour their hives differently from those of their neighbours to prevent bees from mistakenly straying into them in the wind. This would end badly for them. The bees immediately recognise an intruder by smell, so the guards would attack the lost bee at the entrance and sting her to death.
Like ants, bees need to tell their companions where the food is and how far it is from the hive. Their language of communication is dance. When a bee finds food, it returns to the hive and dances. If the food is less than a hundred metres away, the dance is simple and the bee spins around a little, if it is more than a hundred metres away, it swings its abdomen from side to side to draw a figure eight.
The number of wasps depicted by the bee during the dance indicates how far the flowers are from the hive, but her report is not precise. If she was returning home with a strong wind, her fellow bees flying towards it will take longer to reach their destination than she did to reach the hive.
He also tells them which way to fly by dancing. It moves up and down on the honeycomb or on the platform in front of the apiary, depending on where the sun is at that moment and where the food is in relation to it. The bees fly in this direction for as long as the number of eights instructs them. If they do not find what she has promised them at their destination, they freeze a little and start circling over the area. They search it, trying to detect the smell of the food, but also trying to remember their surroundings. They remember the location of the food before they start picking it, not after they have picked it, because the next time they will need their visual memory is when they arrive, not when they leave.
They also circle above the apiary before leaving it. Even now they are trying to remember their surroundings, although it is also possible that they are checking the weather. They do not like rain, wind and cold. If they expect adverse weather conditions, they prefer to return to the hive, but if the conditions are right, they fly more or less straight to the food, except when there is a hill between the hive and them. The bee can also tell her colleagues that the food is on the other side of the hill, but the bees will not necessarily fly over it. They may choose to go around, although it is not clear why.
The bee communicates all this information to her companions by dancing in the darkness of the hive. The other bees “watch” her by touch and smell. This is how they find out what the nectar and pollen she has collected smell like, and they also remember her scent to help them on their way to the flowers she has visited.
Bees are well organised, have an internal compass and a sense of time, but also of temperature. On an extremely hot day, most bees retreat to the shade of the vegetation, leaving only a few sentinels in the apiary. At midday, they flap their wings constantly to cool the brood and the hive, while other workers bring drops of water and drop them on the honeycomb to cool the hive by evaporation. In winter, on the other hand, they huddle close together to maintain a temperature of 18.3 degrees Celsius and eat the honey stored in the honeycomb to replenish their energy.
Unlike bees, sand wasps are solitary. They also have good eyesight and memory, both of which they need to take care of their offspring. The wasp first digs a tunnel in the sand. It bites into the sand and flies away with its mouth full to cover its trail. It loses grains along the way and deposits the rest somewhere. He repeats this until he has dug a suitable tunnel for his brood.
Then he goes hunting. It must provide its first meal for the offspring that will hatch from that one egg rolled in the sand hole, so it needs a caterpillar, bee, spider or fly. When it finds one of these, it grabs it hard with its legs and jaws. He turns it around in them long enough for the barb to strike the nerve centre precisely and inject just the right amount of venom. It must paralyse the victim but not kill it, and the prey must remain alive and paralysed for so many days that it will be unable to resist when the larva starts to gnaw at it.
Who knows how, but the larva knows that it has to start its multi-day quest with the parts of the body that are not vital. This keeps the food alive and fresh for as long as possible. The victim dies only when the larva starts eating its vital organs. The sieve remains underground until summer, except in favourable climatic conditions and in some wasp species when it grows up by spring.
But how do wasps find their way to their burrow to stock it with food for their offspring? By sight. The wasp Ammophila campestris, which makes three or four burrows at the same time and has to fill all of them with prey, depends entirely on recognisable signs. Familiar trees, bushes, plants and debris guide it to its burrows, but if, for example, researchers change these landmarks or put another set of the same ones in front of it, it will miss the burrow.
Sometimes it has problems even without researchers. When the prey is heavy, such as a caterpillar, it has to return to the den on foot and drag it behind it. It cannot recognise its landmarks on the ground, so every so often it releases its prey, rises into the air and finds the next landmark. It descends to the ground again and continues in the right direction.
Rabbit fleas have no such problems. The female has a special compartment in her body for sperm. During mating, the sperm is stored there, waiting for the right moment to be used. Fleas of both sexes and ages feed on rabbit blood all the time, but the flea eggs cannot be fertilised until the female has fed on and digested the blood of a pregnant rabbit.
The premise is logical and fascinating: the flea will hatch its eggs around the same time that the hare gives birth to the bunnies in its underground burrow, and the larvae will have a warm home in the nest and in the hare’s fur. The larvae are initially dependent on drops of blood brought to them by fleas of both sexes, but after a month, when the young rabbits are ready to explore their surroundings, they too are fully developed fleas, ready to go out into the world on the rabbit’s fur and start hopping around.
Collective suicide
For a different reason, vegetarian ostriches are hopping around, living in their underground tunnels in the Arctic tundra. They are not only able to survive under the snow, but also to eat and reproduce normally all winter long, provided the carpet of snow and vegetation is just thick enough to protect them from the elements and they have enough food to eat.
So the winter-born ostriches already have their young in spring, but now there are too many of them in their home and not enough food for them to survive. Overcrowding causes mass psychosis, and hysteria spreads through the sand tunnels and labyrinths. The young stay, but most of the adults and adolescent ostriches head for the sea and rivers. Some fall over rocks and kill themselves on the way to the sea, others jump into rivers and lakes. Most die before they reach the shore, and all the time they are also preyed upon by gulls, eagles, falcons, weasels and other enemies.
This turns their migration into a group suicide and their carcasses become a food supply for the starvation period, but this does not endanger the species, it merely restores the balance. There are just enough left to live normally for six years, or maybe a few more, until the overpopulation period comes again and they rebalance it by mass suicide.
Similarly, the migration of Russian saiga antelope ends every 12 years. In summer, they build up a thick layer of fat to survive the winter. When snowstorms rise, they start to run quickly south or west before the snow advances, as if they were migrating completely at random. At 16 kilometres per hour, they can run continuously for days, cross the frozen Volga and even venture into the frozen Caspian Sea.
But if the snow drifts long enough, thousands of them will disappear due to starvation. Once every 12 years, half the population dies, but the other half has an incredible ability to survive. In spring, it returns four or five kilometres north and gives birth to young, usually twins.
The African locust, which appears in Assyrian and Egyptian graves as part of the diet, is also migrating, and is a particular nuisance to modern man. When a swarm of locusts darkens the sky and eats every leaf and stem it finds on its way, the destruction of the crop is complete.
Winged locusts have two embryos a year, but the babies will only hatch if the soil in which the eggs were hatched is moist. Before they are able to fly, the budgies feed for several months where they were born. Finally, they fly off and when there are enough locusts, a swarm is formed. But now there are so many that they no longer have enough food in their area. To find it, they have to fly elsewhere every day, avoiding completely deserted areas of the desert and areas affected by drought.
But they can only set off once they have warmed up. They become helpless and immobile after sunset, and after a cold night they can give nothing of themselves. At sunrise, each grasshopper first stretches out a little, stretching to let the rays shine on as much of its body as possible. Slowly it comes to life, wiggles a little and finally rises into the air. Before it takes off, it lifts its head into the wind, which it can do because it has receptors on its head that sense it.
At first, the locusts only make short, reconnaissance flights, but when they return, they decide which direction they want to go. They begin to gather until they form one giant formation, rising like smoke to a height of about 30 metres, although some fly lower and some higher, as if checking the strength of the wind. When the weather is fine, they advance at a speed of about four metres per second and, with breaks for feeding, can cover up to 50 kilometres a day. Although they can fly in all directions, they prefer to move on calm days or into light winds.
They are primarily sight-oriented. They look ahead and move forward without hesitation, as long as the images below them are moving backwards from the view. But when the wind picks up and becomes stronger than four metres per second, their image changes: it freezes, or the images in front of their eyes start to move from behind them forward. Then they become completely confused and fall to the ground. They may continue closer to the ground, where the wind is weaker, or they may simply turn away from it.
But when a swarm of locusts takes to the air, it makes a tremendous noise. Each locust rubs the surface of its wing against its thigh to create a metallic sound that seems to tell its distant mates, “Let’s go!” But they sound very differently at mating time. When the sits are lowered to the ground, the male begins to hum seductively with his instrument and the female responds even more gently. During their love song, which is audible even to the human ear, they slowly approach each other and finally fuse sexually.
