ENTOMOLOGY

438 SANITARY ENTOMOLOGYThe species is very variable in abundance, wooded or brushy4andsbeing most favorable for it, particularly when close to cultivated fields,and of course where small mammals are present upon which the immaturestages may engorge, and d.omestic animals for the engorgement of theadults.Other species of Dermacentor include the American dog tick, D. 'Variabilis(Say) Banks, which occasionally attacks man, and the Pacific Coe.sttick, D. occidentalis (Marx) Neumann, which infest various hosts, includingman, in the Pacific region. The life" histories of these species arequite similar to that of t~e spotted. fever tick." Many animals serve ashosts, especially for the immature stages.The winter tick or elk tick, D. albipictua Packard, is a representativeof the group which remains on the host to molt. This form is often aserious pest of horses and cattle and is probably the cause of the deathof many elk on account of its occurrence in great numbers on the animalsduring the winter season. The eggs hatch in the summer or late fall andthe ticks attach in the long winter coat of the host, becoming matureand detaching in one to three months.In tropical America another species of Dermacentor, D. '1litens Neumann,is often the cause of considerable annoyance to horses by itsattack of that host deep in the ears.It was first suggested that a simple scheme for the separation of themore important species by morphological characters, host, and distributionmight be desirable, but on further consideration this idea wasdropped. In the first place, it is very essential, especially in consideringdisease transmission, that the exact species of the possible vector bedetermined. This can always be accomplished best by submitting specimensto a specialist. In the second place there is a general lack offamiliarity among sanitarians and even among entomologists with ticksand the characters utilized in distinguishing different forms. sIn collecting specimens it is well to attempt to secure both sexes. Themales are usually rather smaller and less conspicuous than tbe females,especially when the latter are engorged. The specimens may be preservedin 70 per cent alcohol or 3 per cent formalin solution;BIBLIOGRAPHIC REFERENCESLiterature on ticks has become quite voluminous. Fortunately there isa very complcte bibliography availablc. This appeared in two parts,• The writer (Box flOB, Dallas, Texas) Is prepared to make determinations of the ticksof North America on short notice. In Europe there are a number of systematists inthis group. Dr. G. H. F. Nuttall of Cambridge University, Cambridge, England, wouldno 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 thecontinent. Prof. C. P. Lounsbury, Pretoria, South Africa, is well acquainted with theticks of that region.