438 SANITARY ENTOMOLOGY 



The species is very variable in abundance, wooded or bi'ushy lands 

 being most favorable for it, particularly when close to cultivated fields, 

 and of course where small mammals are present upon which the immature 

 stages may engorge, and domestic animals for the engorgement of the 

 adults. 



Other species of Dermacentor include the American dog tick, D. varia- 

 bilis (Say) Banks, which occasionally attacks man, and the Pacific Coast 

 tick, D. Occident alls (Marx) Neumann, which infest various hosts, includ- 

 ing man, in the Pacific region. The life histories of these species are 

 quite similar to that of the spotted fever tick. Many animals serve as 

 hosts, especially for the immature stages. 



The winter tick or elk tick, D. albipictus Packard, is a representative 

 of the group whicli remains on the host to molt. This form is often a 

 serious pest of horses and cattle and is probably the cause of the death 

 of man}^ elk on account of its occurrence in great numbers on the animals 

 during the winter season. The eggs hatch in the summer or late fall and 

 the ticks attach in the long winter coat of the host, becoming mature 

 and detaching in one to three months. 



In tropical America another species of Dermacentor, D. nitens Neu- 

 mann, is often the cause of considerable annoyance to horses by its 

 attack of that host deep in the ears. 



It was first suggested that a simple scheme for the separation of the 

 more important species by morphological characters, host, and distribu- 

 tion might be desirable, but on further consideration this idea was 

 dropped. In the first place, it is very essential, especially in considering 

 disease transmission, that the exact species of the possible vector be 

 determined. This can always be accomplished best by submitting speci- 

 mens to a specialist. In the second place there is a general lack of 

 familiarity among sanitarians and even among entomologists with ticks 

 and the characters utilized in distinguishing different forms.^ 



In collecting specimens it is well to attempt to secure both sexes. The 

 males are usually rather smaller and less conspicuous than the females, 

 especially when the latter are engorged. The specimens may be preserved 

 in 70 per cent alcohol or 3 per cent formalin solution. 



BIBLIOGRAPHIC REFERENCES 



Literature on ticks has become quite voluminous. Fortunately there is 



a very complete bibliography available. This appeared in two parts, 



^The writer (Box 208, D<allas, Texas) is prepared to make determinations of the ticks 

 of North America on short notice. In Europe there are a number of systematists in 

 this group. Dr. G. H. F. Nuttall of Cambridge University, Cambridge, England, would 

 no doubt be glad to determine specimens sent to him. Professor L. G. Neumann, 

 Laboratorie d'Histoire Naturelle, Toulouse, France, is a leading tick authority on the 

 continent. Prof. C. P. Lounsbury, Pretoria, South Africa, is well acquainted with the 

 ticks of that region. 



