• The Tsetse Fly

  • Why Zebras have stripes………… could it be to avoid a Tsetse Fly?

    A Little History

    The story of civilization is a story of migration and survival, one that includes not only humans, but plants and animals and all species on down to the microscopic.  It was our horses and later ships that transported the most efficient migration of domestic plants and animals.  However,  geography in Africa presented a challenging land mass.  The north-south axis interrupted the movement of horses and limited water transportation.  It was the position on the globe of the African land mass that  impeded the domestic plants and animal along with their humans to migrate.  And, here is why.

    The north south axis where migration is impeded by disease Wikipedia


    Over 2000 years ago Khoisan people who had acquired domestic animals from the Northern hemisphere displaced Khoisan hunter-gathers on this large continent. When horses were made available to tribes of hunter-gathers in West Africa, they transformed into a warfare kingdom.  Cavalry in West Africa north of the  Sahara  were given a huge advantage.  It is similar to the pattern in the 19th century in the Western hemisphere where escaped European horses were acquired by native hunter-gathers.

    In Africa, however,  this advancement from West Africa could go no further south in the continent.  “The 2000 miles of tropical conditions between Ethiopia and South Africa posed an insuperable barrier.” The spread of horses and all domestic animals, which includes the camel, was halted by the climate and disease.  Most noteworthy was trypanosomiasis, Glossina,  carried by the tsetse fly and the horsefly, which threatened both man and beast who were defenceless.  Wild species, such as the zebra and its stripes, had developed their own immunity to such threats.  Did the stripes of the zebra  confuse the fly?  Or was it the white stripe that repelled the fly?



    The Tsetse Fly Life Cycle

    the tsetse fly and illustration of actual size


    The tsetse fly is the size of a large house fly and crudely resembles it.  Both the male and the female fly feed on a blood meal of wild vertebrate animals.  These predators inhabit the tropical waterways of the continent where the equator lies, making a diet of animals in the region.  These flies carry with them an invasive microorganism which causes trypanosmiasis, most commonly known as  sleeping sickness in humans and a tribal word in Africa, nagana, in animals. A variation of the subspecies of trypanosmiasis  evansi is transmitted among camels who have been bitten.

    Once injected, the saliva-borne parasite of the tsetse fly enters the victim’s blood stream and attacks the nervous system.  Large domestic animals,  such as the horse, cow,  goat  and also the camel which migrated from North Africa, have no immunity and cannot survive the tsetse fly’s attack, when it carries this trypanosome organism.  When man is bitten he, too, cannot resist the illness,  African Sleeping Sickness.  Death may occur.  Even, today, it  claims  thousands of cases a year.

    It cannot be overstated that the impact of this small creature, the carrier of trypanosomiasis, who attacks our beast of burden, the horse and the camel  slowed development of an entire continent by enormous proportions.  It stopped man and beast in their tracks for centuries and altered  history.  But, the zebra who grazed the plains of Africa also needed access to water.  And, here swarmed the tsetse fly.  But, the zebra developed a shield to the fly.  A recent study from Lund University in Sweden seems to have given merit to the theory that black and white stripes are an advantage.  These stripes create multiple light patterns and seem to deter the fly who is attracted to black. This experiment was carried out by scientist who used plastic horses painted with stripes of different colors to verify landing patterns of flies.  As of this date the experiment has not been done on Zebras in the wild.

    Sources;                                                                                                                                       Wikipedia                                                                                                                              University of Utah Education Network                                                                                   Guns, Germs and Steel by Jared Diamond                                                                             Brian Hursey,  Food and Agricultural Org. of the United Nations                                       The Journal of Experimental Biology