76 LIFE HISTORY OF NORTH AMERICAN TICKS. 
the host for a considerable time accounts for the fact that the males of 
the larger species, such as A. maculatum and A. tuberculatum, are 
more commonly collected than the females. It has been noted that 
with the species in which the male is small and inconspicuous the 
females have been more frequently collected. 
Genus IXODES Latreille. 
The genus Ixodes is represented by more species in the United 
States than any other genus. On account of this fact, the general 
distribution of the members of the group throughout the country, 
and the occurrence of the species on a large number of smal! mammals, 
no doubt a considerable number of undescribed forms will be found 
in the future. 
The black-legged tick (/zodes scapularis) and the California Ixodes 
(Ixodes californicus) are the species of most importance in _ this 
country. These species are both closely related to the» European 
castor-bean tick (/xodes ricinus), and are thought by Bishopp to 
be only varieties of the European form. This view is also held by 
Nuttall and Warburton. 
None of the members of this genus has been connected with disease 
transmission in this country, but in Germany Jzodes ricinus has been 
shown by Kossel and his associates (1903) to be capable of trans- 
mitting bovine piroplasmosis, and Stockman (1908) has shown it to 
play the same réle in England. 
Ixodes ricinus, on account of its general distribution and impor- 
tance in Europe, has received the attention of a number of investi- 
gators. This species has been studied in England by Wheler (1899) 
and in Germany by Kossel and his coworkers (1903). Jzodes 
pilosus has been studied by Lounsbury (1900-1906) and by Mally 
(1904). The life histories of only two species of the genus, namely, 
Ixodes scapularis and Ixodes kingi, are presented here, although 
several other species are now being studied. All of the species 
observed drop from the host to pass both molts. 
THE BLACK-LEGGED TICK. 
Tvodes scapularis Say. 
DESCRIPTIVE.! 
Adult (Pl. V, figs. 2, 3, 5-8).—Males about 2.3 by 1.25 mm. 
Females, unengorged, from2.5 by 1.25 mm. to 3 by 1.5 mm.; en- 
gorged, about 10 by 7 by 5.5 mm. The females are usually dark 
brown, and the males almost black; scutum and legs in both sexes 
black, or nearly so. Partially engorged females that are nearly 
white, and others that are of a dark red color, are frequently found — 
upon the host. 
1 The capitulum has been included in all the measurements of the length of this and other species 
recorded in this bulletin. 
