POISONOUS INSECTS AND THEIR RELATIVES 407 



Many of the seed-ticks never succeed in reaching a 

 host and consequently perish. When once attached to 

 its host, the cattle tick remains there until its growth is 

 completed. Other species of ticks, however, drop from 

 their host to the ground every time they pass through a 

 molt. Since these ticks must find an individual host 

 after every molt before 

 they can make further 

 growth, they run much 

 risk of never reaching 

 maturity, and many of 

 them must die while 

 young. 



Ticks have assumed 

 great economic impor- 

 tance within the last few 

 years, since it has been 

 learned that they are the 

 carriers of numerous dis- 

 eases among domestic ani- 

 mals. In addition, it has 

 been demonstrated that FlG " iso.-The^outhern cattle tick. 



one species, Dermacentor 



venustus, is the carrier of the Rocky Mountain spotted- 

 fever among human beings. This disease occurs in its 

 most virulent form in the Bitter Root Valley in Mon- 

 tana, but it is known to occur in milder form in parts of 

 Idaho, Wyoming, Utah, and Nevada. The bite of this 

 tick is, of course, dangerous, because of the germs of the 

 spotted-fever that are carried by it and injected with its 

 bite into the blood of the person bitten. 



There are at least four species of ticks that occur in the 



