WE HAD recently moved to a rural area in West Africa. Tropical forest surrounded us. One afternoon my wife walked into the closet and yelled: “There’s a horsefly in here!”
The fly shot out of the closet and into the bathroom. I grabbed a can of insecticide and went after it, shutting the door behind me. The fly was nowhere to be seen. Suddenly it flew at my face. It’s attacking me! Arms flailing, I unsuccessfully tried to knock it down. It zipped to the window. The screen blocked its escape. The fly landed on it.
I took aim and blasted the fly with insecticide. Normally a direct shot like that will kill just about any insect instantly. Not this fly. It took off and continued to buzz around the bathroom.
This thing is tough! I was confident that the insecticide would do its work and the fly would soon drop to the floor. But it did not fall. The next time it landed, I sprayed it a second time. It took off again.
What sort of superfly is this? Two more direct blasts finally killed it.
I put on my glasses and examined the creature carefully. It was bigger than a housefly, though not as big as a horsefly. Its wings were crossed over its back, giving it a more streamlined look than an ordinary fly. A long needlelike proboscis extended from the region of its mouth.
I called to my wife: “This is no horsefly. It’s a tsetse fly.”
The encounter impressed upon me the difficulty of trying to eradicate the fly from its African domain of 4.5 million square miles [11.7 million sq km], an area larger than that of the United States. Why do people want to exterminate it? Three charges are leveled against it. Charge one:
It Feeds on Blood
There are 22 different species of tsetse flies. All live in sub-Saharan Africa. All, both males and females, gorge themselves on vertebrate blood, sucking up as much as three times their weight in blood with a single bite.
They feast on a wide range of grazing animals—both those native to Africa and those that are not. They bite people too. The bite is a deep, bloodsucking stab, sharp and painful. It itches and hurts at the same time. It raises a welt.
Tsetse flies are skillful at their work. They do not waste time buzzing around your head. They can fly at someone like a bullet and somehow put on the brakes and land on the face so gently that they are not felt. They can be like thieves; you sometimes do not know they have stolen some blood until after they are gone—when all that remains for you to do is assess the damage.
Usually they go for exposed flesh. (They seem to like the back of my neck!) Sometimes, however, they decide to crawl up a trouser leg or shirtsleeve before tapping a blood vessel. Or if they choose, they can bite through clothing—that’s not a problem for an insect that can pierce even the tough hide of a rhinoceros.
People accuse the tsetse fly of being not only smart but also cunning. Once when I tried to kill one with insecticide, it flew into my closet and hid in my swimming trunks. Two days later when I put on the trunks, it bit me twice! On another occasion a tsetse fly hid in my wife’s purse. She took the purse to an office, and when she reached inside, the fly bit her hand. Then it flew around the room, causing havoc among the office workers. Everybody stopped work to try to swat it.
So the first charge against the tsetse fly is that it is a bloodsucker with a painful bite. Charge two:
It Kills Animals
Some varieties of tsetse flies transmit a disease caused by tiny parasites called trypanosomes. When the tsetse fly sucks the blood of an animal that has the disease, it swallows blood containing the parasites. These develop and multiply inside the fly. When the fly bites another animal, parasites pass from the fly into the bloodstream of the animal.
The disease is trypanosomiasis. The form that occurs in animals is called nagana. Nagana parasites thrive in the bloodstream of many animals native to Africa, especially antelope, buffalo, bushpigs, duikers, reedbuck, and warthogs. The parasites do not kill these animals.
But the parasites devastate livestock not native to Africa—camels, dogs, donkeys, goats, horses, mules, oxen, pigs, and sheep. According to National Geographic magazine, nagana kills three million cattle each year.
Cattle herders, such as the Masai of East Africa, have learned how to avoid the areas where tsetse flies are most plentiful, but drought and lack of pasture sometimes make this impossible. During a recent drought, four families who kept their 600 cattle together were losing an animal each day to the fly. Lesalon, a family elder among them, said: “We Masai are courageous people. We spear the lion and face the charging buffalo. We club the black mamba and confront the angry elephant. But with orkimbai [tsetse fly]? Helpless we are.”
Drugs exist to cure nagana, but some governments permit their use only under a veterinarian’s supervision. There is good reason for that, since partial dosages not only doom the animal but generate parasites that are resistant to drugs. It may be difficult for the cattle herder in the bush to find a vet in time to treat his dying animals.
The first two charges against the tsetse fly have been proved beyond dispute—it feeds on blood and spreads a disease that kills animals. But there is more. Charge three:
It Kills People
Humans are not afflicted with nagana trypanosome. But the tsetse fly delivers another type of trypanosome from human to human. This form of trypanosomiasis is called sleeping sickness. Do not think that a person with sleeping sickness merely sleeps a lot. The disease is not a blissful sleep. It begins with malaise, fatigue, and a low fever.
After that come prolonged drowsiness, high fever, joint pains, swollen tissues, and enlarged liver and spleen. In the final stages, as the parasites penetrate the central nervous system, the patient suffers mental deterioration, seizures, coma, and death.
In the early part of this century, outbreaks of sleeping sickness ravaged the African continent.
Between 1902 and 1905, the disease killed about 30,000 people near Lake Victoria. In the decades that followed, the disease spread into Cameroon, Ghana, and Nigeria. In many villages a third of the people were infected, requiring the large-scale evacuation of people from many river valleys. Mobile teams treated hundreds of thousands of people. It was not until the end of the 1930’s that the epidemic faded and died.
Today the disease afflicts some 25,000 people each year. According to the World Health Organization, over 50 million people in 36 sub-Saharan countries are at risk of contracting the disease. Although sleeping sickness is fatal if untreated, drugs exist to treat it. Recently a new drug called eflornithine was developed to treat the disease—the first such drug in 40 years.
Humans have waged a long war against the tsetse fly and the disease it carries. In 1907, Winston Churchill wrote of a campaign to eradicate the tsetse fly: “A fine net is being woven remorselessly around him.” Looking back, it is evident that Churchill’s “fine net” had large holes in it. States the book Foundations of Parasitology: “So far, 80 years of tsetse eradication have had little impact on tsetse distribution.”
A Word in Defense
American poet Ogden Nash wrote: “God in His wisdom made the fly, and then forgot to tell us why.” While it is true that Jehovah God is the Creator of all things, it is certainly not true that he is forgetful. Many things he allows us to find out for ourselves. What then of the tsetse fly? Is there something to be said in defense of this apparent villain?
Perhaps the strongest defense so far is that its role in the destruction of cattle has worked to protect native African wildlife reserves. Vast areas of Africa are similar to the grasslands of the western United States—the land itself is capable of supporting domestic livestock. But thanks to the tsetse fly, domestic animals are killed by trypanosomes that do not kill native grazing animals.
Many believe that if it were not for the tsetse fly, the great wildlife reserves of Africa would have long ago been replaced by herds of cattle. “I promote tsetse,” said Willie van Niekerk, a guide in a Botswana wildlife reserve. “Eliminate the tsetse and cattle will invade, and cattle are the despoilers of Africa, bulldozing the continent into one big wasteland.” He added: “The fly must stay.”
Not everyone agrees with that, of course. The argument does little to convince the man who watches his children or cattle suffer from trypanosomiasis. Neither does it convince those who argue that Africa needs cattle to feed itself.
Nevertheless, there is undoubtedly still much to learn about the role the tsetse fly plays in nature. Though the charges against it seem strong, perhaps it is too early to make a judgment.
Speaking of flies, one has just flown into the room. Excuse me while I make sure it is not a tsetse.