Origin and Spread of Important Insect Pests of Animals

As FAR BACK as the days of Pliny in the first century, and probably long before, horses, cows, sheep, goats, dogs, and chickens were known to be infested with fleas, bots, and lice. Until the white man arrived in America not one of these animals had been present on this continent for a long time, with the possible exception of the dog. It is natural to assume therefore that all of the specific parasites that take so large an annual toll of our domestic animals were brought to the Western Hemisphere along with their hosts. In the geological past, long before even the most remote historical periods, the American Continent was well supplied with ungulates, or hoofed animals. A great many species of wild horses were well established over much of the country, and elephants and camels were then indigenous. The hoofed animals disappeared during the early Quaternary geological period, estimated at a million years ago. The stony records of paleontology disclose a remarkable and interesting coincidence. In the Oligocène period some 40 million