390 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 3 



of ingress of secondary infection. Thus ticks are of distinct impor- 

 tance aside from the part which they play in transmitting specific 

 diseases. 



LIFE HISTORY AND HABITS 



The life histories and peculiar adaptations of ticks to various con- 

 ditions are interesting, and a knowledge of them is of much im- 

 portance in studying their relations to disease transmission, and 

 in devising methods of control. 



In general ticks have four distinct developmental stages; the 

 egg, the larva, or seed tick, the nymph, and the adult, male and 

 female. All ticks require blood for their development and repro- 

 duction. The eggs are usually about one-fortieth inch long, oval 

 and yellowish to dark brown in color. The eggs are laid in masses 

 of a hundred or so up to 10,000 or 11,000, As the embryos develop, 

 the eggs show a distinct whitish spot on one side. This becomes 

 more pronounced as development progresses. The eggs hatch into 

 six-legged seed ticks which are active in most species. After a meal 

 of blood the seed ticks molt their skins and gain a fourth pair of 

 legs. They are now known as nymphs. In some species there are 

 two or three nymphal stages, the molts following blood meals. At 

 the final nymphal molt the adult males and females are produced. 

 In the family Argasidae, or soft-bodied ticks, the sexes are similar 

 in size and general appearance, and both, with few exceptions, en- 

 gorge with blood. In the other family, laiown as Ixodidae, or hard- 

 back ticks, the males may or may not attach to animals. The fe- 

 males attach, and the rear portion of the body, being elastic, stretches 

 so that when fully engorged the female is little more than a bag of 

 blood, the head and legs appearing relatively small. Mating usually 

 takes place on the host. When replete with blood the females let 

 go their hold on the host and seek a protected place for laying their 

 eggs. Attachment to a host and feeding are accomplished by in- 

 serting the beak or hypostome into the skin. The beak is provided 

 beneath with rows of backward projecting spines which serve to 

 attach the parasite firmly. Near the tip, on the upper side, are two 

 cutting jaws or mandibles which work sideways. These are the 

 principal cutting organs. The palpi, which are sensory organs 

 forming a sort of sheath at the sides of the hypostome, are bent 

 aside as the mouthparts are inserted. 



There are many interesting modifications in the life cycles and 

 habits of the different kinds of ticks by which they have adjusted 

 themselves to the habits of birds or animals upon which they feed, 

 and to the conditions under which they live and develop. One way 

 in which the ticks vary greatly in habits is in connection with the 

 number of times they leave the host to molt their skins. This has an 



