402 ANNUAL KEPORT SMITHSONIAlSr INSTITUTION", 19 33 



Undoubtedly the pest can be greatly reduced in numbers by dipping 

 infested domestic animals during warm periods at intervals not to 

 exceed one month. Proper pasture rotation will no doubt also tend 

 to reduce its abundance. 



THE AMERICAN DOG TICK OR EASTERN ROCKY MOUNTAIN SPOTTED 



FEVER TICK 



In recent years the American dog tick, Derviacentor variabilis, 

 has earned the sobriquet of the Eastern Rocky Mountain spotted 

 fever tick. Until this tick was definitely connected with the trans- 

 mission of this dread disease of man in the East the species was 

 generally regarded as of little economic importance, although at 

 times it becomes quite troublesome as a parasite of dogs, horses, and 

 cattle. 



It is widely distributed over the eastern two-thirds of the United 

 States and also occurs in California. In distribution, therefore, it 

 almost occupies the portions of the United States not covered by the 

 Rocky Mountain spotted fever tick. It is especially abundant along 

 the coast from Cape Cod to extreme southern Texas. 



It has been found to pass the winter succesfully in the seed tick, 

 nymph, and adult stages. It is very little affected by low tempera- 

 tures and the immature stages may become attached to animals dur- 

 ing mild periods in midwinter at the latitude of Washington. In 

 the spring all the stages of the tick become active and the adults are 

 prone to attack the larger domestic animals and man, although they 

 clearly prefer the dog and its relatives as hosts. The various stages 

 are shown in the accompanying plate (pi. 4, fig. 2, to pi. 7, fig. 1). 

 The ticks drop off the host for each molt. The seed tick and 

 nymphs are found on various small wild animals but appear to pre- 

 fer meadow mice, pine mice, and white-footed mice. (See pi. 7, 

 fig. 2.) These little animals are very abundant in the wooded 

 country and doubtless the young ticks have little difficulty in finding 

 a host upon which to engorge. It is not unusual for the females to 

 lay from 5,000 to 7,000 eggs, and all of the stages are very tenacious 

 of Jife. It has been found that the seed ticks, for instance, live at 

 least as long as 12 months, the nymphs 12 months, and the adults 14 

 months. 



The fact that the species feeds upon a number of different animals 

 gives abundant opportunity for them to pick up the organism of 

 Rocky Mountain spotted fever from any susceptible host. This 

 generalized feeding habit also makes control very difficult. The 

 number of the ticks can be distinctly reduced in a given area by 

 dipping infested dogs and other livestock in a suitable tick-destroying 

 material or, in the case of pet dogs, by systematically picking the 



