We think we know them because they are around us every day, and yet…
Even if flies sometimes kill or transmit disease, they also know how to make themselves useful…

KILLER FLIES

Everyone knows: flies like to visit us wherever we are. We also know that they can transmit diseases. What is less well known is the fly’s ability to kill. Devouring man or animal, the Old World Screw-worm fly is indeed a killer.
Their misdeeds began with the conquest of Latin America. When Indians imprisoned by the Spanish were branded with a hot iron, the flies took advantage of the wounds to proliferate and kill. Explanation: the tactic of the Old World Screw-worm fly is to locate a wound in which it can lay its eggs, then the carnivorous larvae hatch and enjoy their meal within the wound, nibbling away at the victim day after day. The situation becomes more terrifying yet when you consider that a female can lay up to 4000 eggs…

To fight against these devastating flies, American fly hunters have resorted to nuclear physics… atomic flies are here! The objective is to sterilise the flies using Gamma rays and to replace normal males with these sterilised atomic flies, which are unable to reproduce. Since female flies mate only once, mating with a sterile male means that they cannot give birth to future generations. In certain zones, millions of atomic flies have been released. As in Nicaragua where numerous aerial drops of the atomic flies are made each night. A dozen light bombers are at work each week, dropping close to 100 million atomic flies over the combat zones. In Nicaragua today the man-eaters are on the decline.
Other countries of Central America will soon be protected by sterile atomic flies thanks to an international cooperation programme direction by the FAO, a United Na-tions agency.
But the war is costly, several hundreds of millions of dollars…

HEAVY SLEEPERS

Responsible for what is known as "sleeping sickness", the tsetse flies found in Africa seek out watercourses in which crocodiles are one of their favourite prey. With its needle-like proboscis, used like a drinking straw, the tsetse fly sucks blood, at the same time introducing parasites – trypanosomes – into its host. These parasites then migrate towards the brain of the victim, who is plunged into a deep sleep. These flies have cause great devastation over the years, notably in the Congo basin in 1930: close to 500,000 deaths.

In the field, special French forces of the IRD (Development Research Institute) and the CIRAD (Centre for international cooperation in agricultural research) set out to search for efficient solutions against these pernicious insects. The tsetse flies are nowadays tracked by satellite!
The method combines the data provided by the satellite images on the vegetation, watercourses, and presence of animals, to predict the zones in which the tsetse will proliferate so that traps can be implanted there. Today, 100,000 deadly traps have been planted throughout Africa, but their cost remains high…
Nevertheless the situation is urgent because the tsetse flies proliferate very quickly. They don’t lay eggs but give birth to one gigantic larva every ten days. Within about half an hour, these larvae metamorphose into nymphs, which give rise to the new generation of tsetse flies. Today, entire regions of Africa are deprived of support for the battle against tsetse flies, and in some villages, they continue to contaminate three people out of four.

FLYING MACHINES

The fly is in certain aspects a “technological marvel”. Its movements are very elabo-rate and its sensory system is particularly well developed.

The principal element of its mobility: its wings. In 1947 researchers began to interest themselves in the formidable flying machine that the fly represents. Research that also incited the interest of the aeronautical industry looking at eventual applications for flight stabilisers in aeroplanes. The fly possesses two small pistons behind its wings, which enable it to take off and to not fly around in a circle. The fly’s wings can beat up to 330 times per second… To facilitate flight, the fly has numerous systems that help it to evaluate flight conditions. The two antennae situated between its eyes act as speedometers and allow it to measure the wind. Automatically, the information collected by these antennae is directly transmitted to the wing adjustment system. It is this system also that allows the fly to know whether or not it can take off, given the wind speed. In flight, the fly is particularly aerodynamic because the hairs present on the top and on the sides of its wings improve the passage of air.

The fly’s sensory system is also highly specialised. Vision first: the fly’s eyes are composed of 3000 individual lenses that give it 360° vision. Moreover, the fly’s vision is like a slow motion film because it handles 200 images per second, whereas hu-mans can handle only 12; which explains why the fly is so difficult to swat… Next, smell: in the fly this sensory organ is situated on the antennae. The sense of smell is sometimes very highly developed; the Calliphora fly for example is capable of detect-ing a decomposing body from a distance of several kilometres. Finally, taste: this or-gan is situated at the end of the proboscis, and also on the feet. The end of the pro-boscis enables the fly to eat and to dissolve its food. The feet allow the fly to taste and to identify its potential meal, which explains why the fly tramples over its food for a long time before starting to eat.

COMPLICATED SEXUALITY

The fly’s wings are essential in courting behaviour and copulation. Indeed, in the male fly, wing beating is a means of seducing the female and of initiating the sexual act.

As in ants, pheromones are also an essential element of the sexual game in flies. These odorous substances that they emanate set off and regulate the courtship. Once the pheromones are recognised and accepted by each partner, the game be-gins with the male, which starts to tap the rear end of his companion to verify its sex. Then the male begins to sing with its wings to seduce the female before licking her sexual organs. Eventually the signal will be given to curve the abdomen and get down to business.

Some scientists are fascinated by flies and their sexuality. Jean-François Ferveur of the CNRS (National Centre for Scientific Research) has confirmed that pheromones were essential in finding a partner. He carried out two experiments: the first consisted of feminising the brain of a male, which immediately began to be court another male. In the second experiment, a male was perfumed with female pheromones. Having now become a transsexual, the perfumed fly had to submit to the advances of an-other male.
Through his experiments, Jean-François succeeded in demonstrating that flies have in a way a double sexual identity…

AQUATIC FLIES

For some flies, hot springs, oil pools and certain lakes are truly a paradise. An exam-ple is the Ephydra fly which has chosen to live in the salt lakes of California, where predators are rare, because of the extreme climatic conditions. These flies survive because they use the only food source found in these lakes: the microscopic algae that manage to grow in these dead waters.
To do so, they have invented scuba diving, using, in the guise of an individual breath-ing apparatus, a bubble of air, which enables them to breathe underwater and gives them a chrome-plated look.

In Mexico, Pedro… is a fly fisherman, a job that allows him to support twelve children. Once fished, the flies are first dried then ground. The powder is then mixed with eggs and rolled out to form flat cakes. But Pedro is not the only one who eats flies…

FLIES ARE DELICIOUS

Indians were the first to come up with the idea of eating flies. What motivated them were the taste and above all the nutritional value of flies. But also because flies were abundant in the region… and hence represented a plentiful source of nourishment.

This is something that others have understood: entomophages, in other words, insect eaters. Among them is Julietta Ramos Eloduy of the Institute of Biology at the UNAM (Autonomous National University of Mexico) in Mexico City, doctor and insectivore. She shares the opinion of the first Indian fly eaters. In many ways, these insects pos-sess nutritive qualities way superior to those of our modern diet: taste, digestibility, and protein content. But there are many preconceived ideas about eating insects and Julietta would like to see these disappear. Her argument is irrefutable: there is an abundance of insects all around us and they represent an unlimited stock of protein. Therefore, why not use them as a solution in the battle against famine throughout the world.

DOCTOR FLY ? WE HAVE AN EMERGENCY…

Some flies practice medicine against their will!
More exactly, their larvae present a real therapeutic interest.
Particularly precious to surgeons, they attack exclusively the dead tissue of wounds. Dr John Church, known as “Maggot Man”, is a specialist in surgery assisted by fly larvae. This technique is used principally when antibiotics or conventional surgical methods have failed.

In John’s view, surgery demands too many staff. Whereas a single fly can produce enough maggots to treat five patients 24 hours a day. His treatment kit, consisting of 500 sterile maggots, costs only around 100 euros ($100 - £70). To obtain these ster-ile larvae, a top-secret process is used at the world’s only maggot farm in Wales.

Close to 300 “maggot therapy surgical centres" have been set up in the United King-dom. But despite its proven and observed effectiveness, maggot therapy remains marginal due to the many inhibitions associated with these tiny crawling creatures.

ELEMENTARY MY DEAR MAGGOT !

Flies and maggots have another rather unusual field of action: forensic police investi-gation.

Dr Marcel Leclerc, the father of forensic entomology, has made maggots and flies his most precious allies during his investigations… Indeed, he uses these small crea-tures to determine the time of death of victims and the circumstances of their mur-ders. And his diagnoses are often deciding factors. In part thanks to the study of the development of maggots laid in the body. And also because several types of fly suc-ceed one another on the same corpse. All these elements enable Marcel to reconsti-tute chronologically the exact circumstances of a murder. The first squad of flies to take interest in cadavers is that of the Calliphora blow fly, which intervenes in the first hours following death. Then the second squad, composed of egg-laying green blow-flies, arrives eight to ten hours after death. Finally, then last to show up are the bee-tles, acarians and other flies…

With more than 100 criminal cases solved by “flies” to his credit, Marcel has become an undeniable expert.

ARTISTIC FLIES

According to psychiatrists, the fly is one of the insects that touches our subconscious mind most often, and this is well understood by artists…
In Renaissance art, flies abound in Italian and Dutch painting. To show their moder-nity, artists made the fly into a fashionable trompe-l’oeil. More symbolically, the fly represents the ephemeral side of life.
Today, Jean-Marie Gheerardyn pushes the symbolism even further. This extraordi-nary artist, simultaneously fly killer and “artistic dictator”, as he likes to be called, sees the fly as a material with which he can express his macabre visions. Dedicated to all human hecatombs, Gheerardyn’s works are composed of dead flies, intricately sorted in advance.

OUR COUSINS THE HUMAN FLIES?

No, David Cronenberg’s film “The Fly” has not become a reality! But in the same spirit, one fly, the Drosophila, also known as the fruit fly, is astonishingly close to hu-mans!
Drosophilae have cells identical to those of humans and reproduce rapidly: one gen-eration every three weeks. This fly is therefore ideal laboratory material. For the needs of certain research programmes, the genetic code of drosophilae can easily be manipulated, giving rise to new races of flies: mutants. Certain mutants might have a leg in the place of an antenna, or atrophied wings.
Today thousands of mutants are patented like any other invention.
We also have flies to thank for the discovery of numerous genetic diseases, and also for that of Viagra, and perhaps tomorrow a step towards immortality and the under-standing of sexual attraction in humans.