384 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



The stable-flies develop in much the same way, and under the 

 same conditions as the house-flies, but they are more apt to be 

 found in cow manure or old straw or other decaying vegeta- 

 tion, than in horse manure. The stable-fly also takes longer 

 to complete its development than does the house-fly, often 

 requiring three or four weeks to pass through the larval and 

 pupal stages. 



Stable-flies are among the most serious pests of cattle and 

 horses, biting them severely and causing considerable swellings 

 in the places where they bite. They have recently been the 

 subject of particular study and investigation because they have 

 been suspected of being intimately connected with the dis- 

 tribution of that mysterious disease known as poliomyelitis, 

 or infantile paralysis. This disease, which has been slowly 

 spreading over America as well as most European countries, has 

 baffled the skill of physicians because they have been unable 

 to determine how it is transmitted. Experiments have been 

 made which show that stable-flies are capable of transmitting 

 the disease if they are allowed to bite first an infected and then a 

 healthy monkey. While this by no means proves that it 

 really spreads the disease among human beings, it yet adds 

 greatly to the evidence against this insect, so that the flies 

 should be destroyed whenever possible. The same measures 

 that are necessary for the control of the house-fly would aid 

 materially in controlling this insect also. 



Other Diseases Carried by Insects. There are many other 

 diseases that are known to be transmitted by insects. Sleep- 



FIG. 171. Filaria in the thorax, head and labium of a mosquito. (After 

 Castellan! and Chalmers.) 



ing sickness and other diseases caused by trypanosomes and 

 carried by tsetse-flies have been discussed in Chapter XXVIII, 

 and in Chapter XII it has been shown how mosquitoes carry 



