TICKS — BISHOPP 391 



important bearing on the disease-transmitting possibility of a given 

 species, and on methods of control. For instance, some ticks find a 

 new host each time they feed, after dropping off the previous host to 

 molt their skins. This allows a given tick an opportunity to pick up 

 an infection from one host and transmit it to another. Some adults 

 also have the habit of engorging with blood several times at inter- 

 vals of a few weeks to several months, using a different host for each 

 engorgement. 



The habit of engorging quickly and dropping for each molt makes 

 control more difficult. Again, we find some ticks, such as the cattle 

 fever tick, that have the habit of remaining on the host during 

 molts. In the case of ticks with this habit such diseases as are 

 carried must be transmitted hereditarily, i.e., from one generation of 

 ticks to the next, through the egg. Some species of ticks will 

 engorge on many different kinds of animals, while others are very 

 restricted in this respect. This question of host preferences and 

 host restriction is also an important one both from the standpoint of 

 disease transmission and that of susceptibility to control. It is 

 apparent that a species of tick which attacks only a few kinds of 

 animals is likely to be more easily controlled or eradicated than a 

 species which will feed upon any animals which come in contact with 

 it. The cattle tick is a form which is restricted in the number of 

 hosts upon which it will feed. This fact has made its eradication 

 possible by regularly dipping its usual hosts, i.e., cattle, horses, and 

 mules, or by keeping these animals out of pastures infested witli 

 the tick. These methods, put into effect by the Bureau of Animal 

 Industry in cooperation with the various States, have resulted to 

 date in the eradication of the tick from 651,311 square miles of terri- 

 tory in the United States, or about 89 percent of the area originally 

 infested. (See fig. 1.) Many other kinds of ticks in this region 

 which feed on a greater variety of animals and drop for their molts, 

 were not materially affected or were only temporarily reduced in 

 numbers by these eradication practices. 



Some of the more interesting and economically significant of these 

 habits will be brought out under the discussion of the different 

 species. 



FEEDING HABITS 



Ticks will not develop without partalring of blood. Most ticks 

 attach firmly to their host while feeding, and the blood is taken up 

 slowly. The nymphs of the spinose ear tick, for example, ma}' take 

 as long as 7 months to become engorged. The time for engorgement 

 of each of the different stages in most species, however, usually 

 ranges from 3 to 12 days. Certain species engorge with extreme 

 rapidity, and attachment in such cases is less firm, so that the ticks 



