copyright Mona Lisa
A world premier: the indiscrete eye of the electron microscope unveils the secret life of acarians. Scenes never before witnessed will take us to the heart of this invisible world that is part of our daily lives
An invisible multitude, crawling, omnipresent, envelops us. Creatures from the beginning of time, practically unchanged for four million years. Indestructible survival machines capable of adapting to extreme conditions. With the acarians, we will pene-trate into the parallel universe of the conquerors of the infinitely small.
As Professor Coineau, director of the arthropod laboratory at the National Museum of Natural History in Paris, emphasises: “They are everywhere, except in the air, which is inaccessible to them because they have no wings. From the ice of the Antarctic to the boiling springs on the ocean floor, from the Namib Desert to the forests of Norway, nothing escapes them. Neither the soil nor water nor plants nor animals.”




For these "squatters", each living being is a micro-planet. The place where they are born, eat, reproduce, eat each other, die.
With close to half a million identified species (acarologists think that twice as many may exist) the acarian order, distant rela-tives of crustaceans, have their own predators, prey and scav-engers. Each species has its own shape, its specificity. Some are ovoid; others look like worms or miniscule spiders, their closest cousins.
In fact, the red spider mite, that ravager cursed by gardeners, is not a spider but an acarian. Visible to the naked eye, it is one of the family’s giants. However, it cannot rival the tick, which, once engorged with its victim’s blood, can measure up to three cen-timetres in size. At the other end of the scale, the smallest known acarian inhabits the trachea of bees and measures only 100 microns.


Between these two extremes, hundreds of thousands of species proliferate, not all of them inoffensive to humans. In our imme-diate environment, we find thirty or so species. Our most loyal companion is without a doubt the house dust mite. Since hu-mans have existed, this detrivore has accepted the duty of get-ting rid of the human’s dead skin cells (we lose up to three grams of squames each day). For thousands of years, this co-habitation has been rather well tolerated, few people being dis-turbed by the presence of these “exfoliating machines”.




Apart from these undesirable companions, other species pre-sent what we regard as the most unpleasant behaviours. Such as the Sarcoptes, which, like moles in a garden, burrow through our epidermis, giving rise to the condition known as scabies. And those harvest mites that, at the end of summer, attack our calves, leaving us with stinging souvenirs. They might look quite inoffensive, compared with their Asian cousins that inoculate the bacteria responsible for the fatal scrub typhus. For many acarians also play the role of used syringes.


In this pernicious game, ticks are the most formidable of play-ers. Representing the Number Two parasitic scourge in the world, these congenital vampires need fresh blood to complete the three metamorphoses that will turn them into adults. Imme-diately after birth, the little tick waits in ambush in the grass for its victim to pass by. Being blind, it localises its victim using the carbon dioxide detectors situated on its front legs. As soon as it is within range, the tick throws itself onto its prey and, latching on to the skin through its mouthpart, it gorges itself with blood. If the host is healthy, well and good. But if the host carries dis-ease, the young tick will become a vector, transmitting the dis-ease to its next victim. Once satisfied, the young tick lets go, di-gests and metamorphoses. When they reach adulthood, the males stop eating. Only the female tick continues to bite. She then partakes of an extravagant meal, which will cause her to grow from a few millimetres to more than two centimetres in size. So that she can gorge herself at liberty, she secretes an anaesthetising cement around her mouthpart, which enables her both to adhere to and to be tolerated by her prey. When sa-tiated, she lets herself fall into the grass where she lays up to 4000 eggs, possibly transmitting the pathogenic agents for which she is the vector.




Luckily, not all acarians are dangerous parasites. Some are even quite pleasant. For example, the soil acarians, a popula-tion of tiny creatures essential to life in the plant world, and therefore to our own survival. Beneath our feet, they decom-pose, chew, digest, and recycle organic debris, transforming it into humus. Without their contribution, forest floors would be two metres deep in leaves that the trees are unable to assimi-late and the plants would die, deprived of nutrients.
Some acarians are so useful that humans have undertaken to domesticate them. This is true for the Phytoseilus, acarians that prey on other acarians that feed on plants, sucking out the cell contents. As the feeding habits of the latter represent a real scourge for plant growers, experiments have been carried out in which the predators were released. To the researchers surprise, they found that the actions of these “terminators” enabled a 75% reduction in the use of pesticides, to which moreover the plant-suckers had started to develop resistance. Another advan-tage: once the prey were eliminated, the predators regulated their own numbers by devouring each other, thus avoiding all risk of uncontrolled proliferation.




Did you know that the Phytoseilus have even been promoted to the ranks of employees at Eurodisney Paris and Disneyworld in Florida? For the well-being of visitors, but also of Mickey, Minnie and the others, they have been put in charge of protect-ing from parasitic attack all the plants that enliven and give col-our to these theme parks, while making the use of pesticides unnecessary in an environment with so many children.


In our homes, dust mites love humidity, heat, textiles and of course, dust… and their favourite room is the bedroom. And thus the dust mites like to nest in the most intimate of places. Which explains, among other things, the phobia that some peo-ple have about these creatures. Especially since we spend a third of our lives in bed… So, for an acarian-free home, the rec-ipe is simple: tiles or linoleum on the floor, washable paint on the walls, no curtains, bed bases with slats or springs, mattress covers and pillows treated against acarians, synthetic pillows and duvets washed regularly… and since the acarians detest dry air, being aired, the vacuum cleaner and anti-acarian treat-ments, controlled mechanical ventilation is a good idea!




- Close to 500,000 species of acarian have been recorded. Their size varies from 100 microns to 3 centimetres.
- Beneath each of our footsteps, almost 4000 soil acarians can be found.
- There are thirty domestic acarian species, which die when the humidity level falls below 45%, while the temperature drops to 20°C.
- Acarians are not found in houses above an altitude of 1300 metres.
- In France, 80 % of asthmatic children are allergic to acari-ans.
- There are up to 15,000 acarians in one gram of dust, which represents 10 micrograms of allergens.
- The allergens are destroyed when they are exposed to a temperature of 100°C for 30 minutes.




Acarus siro occupies a special place among acarians. Certain gourmets love them. Usually those that love the taste of authen-ticity. For Acarus siro lives in the rind of certain traditionally crafted cheeses, endowing them, it seems, with an incompara-ble matured quality… Be aware though, that real cheese lovers eat the cheese with its rind… and its acarians!
Take Marinette, for example, a traditional cheese maker in Au-vergne. In Marinette’s cheese factory, the real artisans are the acarians. For Marinette, the acarians give her cheese an un-beatable savour, even though their role in the maturing of the cheese remains unknown. The taste of acarians was already well appreciated in former days; some would even eat them for breakfast.
The Acarus siro acarians are in fact completely inoffensive, al-though people who manipulate them too often can develop al-lergies. They are also “social animals”, living in groups and families, and proliferate very rapidly. All to the delight of the people of Auvergne who buy the cheeses occupied by these rather original inhabitants. Paradoxically, in the same region, you don’t often hear people talking about these artisans – it’s a taboo subject – for nobody wants to reveal the secret of these unique cheeses.




In the Jardin des Plantes (botanical garden) in Paris, there is an area where pesticides are forbidden. Live acarians are sorted and cared for there… Professor Coineau, director of the labora-tory for arthropod research, has created a sanctuary for them. There, in this unique “mini-zoo”, the public can discover the fas-cinating world of soil acarians, thanks to the most up-to-date technology, enabling us to penetrate the invisible. Collecting all his acarians by sampling earth and humus from forests or sand from deserts, Professor Coineau has a real passion for the creatures, and has discovered the many specificities of each variety of acarian. Some are experts in camouflage (the “oribat-ids”), others are predators (the “labidostomas”)… A passion that this mad acarologist attempts to pass on to others, day after day, and sometimes it works…




The giant of acarians, the tick is a prolific creature, a vector of disease, and above all, a true vampire.
Like many other creatures of its kind, the tick is an impressive sexual performer. Obsessed with reproduction, the tick must metamorphose three times before it reaches adulthood and can begin to copulate. An ephemeral actor in the community, the male tick dies after coupling. The female tick can lay from 3000 to 4000 eggs, as long as the larvae have enough to eat…


But like lice, ticks must feed on blood to survive. This is why they are also veritable vampires. In fact, it is only after a meal of blood that each of the three metamorphoses takes place, bring-ing the tick to its adult stage. Only the female bites, gorging herself with blood to increase her weight 200-fold. To complete her blood meal, the tick must suck for eight days. And the equipment she uses resembles a drilling platform… The tick has a mouthpart with multiple teeth and two fang-like append-ages resembling knives that move apart to cut the skin as it is penetrated. At the same time, the tick produces a cement with an anaesthetising power that enables it to pierce the skin with-out detection and its mouthpart to remain solidly anchored in the skin.


It is during this operation that the tick can transmit the diseases of a carrier to a healthy individual, most often after 48 hours of attachment… Ticks will attack with indifference humans, wild or domestic animals that pass through grasses and undergrowth within range of the its mouthpart. Present on every continent, ticks carry numerous diseases, some very serious. A fact which makes the tick the number two parasitic scourge of the modern world, second only to the mosquito.

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