THE BLACK-LEGGED TICK. 81 
same time was sloughed off on October 1, being but slightly engorged 
at that time. The reason these two females did not engorge more 
rapidly is not known. It was not due to a lack of fertilization, as 
mating took place while the ticks were on the host. A slightly en- 
-gorged female that was applied to a bovine host on December 26, 
1907, dropped 8 days later fully engorged, measuring 10 by 7 PY 
5.5 mm. 
LIFE CYCLE. 
Oviposition may commence in 15 days after dropping. Three 
thousand or more eggs are deposited by the engorged tick. In winter 
at a mean temperature of 61° F. incubation may take place in 72 
days, a total effective temperature of 1,318° F. being required. Larve 
may engorge in 3 days and at a mean temperature of 77° F. com- 
mence to molt 23 days later, an accumulated effective temperature 
of 786° F. being required. Nymphs may engorge in 3 days after 
being applied to a host. In summer 25 or more days appear to be 
required for the nymphal molt. A total effective temperature of 
at least 1,017° IF. appears necessary for this transformation. A 
slightly engorged female collected on a dog reattached and engorged 
upon a new host in 7 days. 
ECONOMIC IMPORTANCE, 
The black-legged tick is not known to be of any great economic 
importance. In Germany and England a closely related species, 
_ Ixodes ricinus, transmits bovine piroplasmosis and it is possible that 
this species may do so. While this tick has been found by Prof. 
H. A. Morgan to be rather numerous on cattle in northern Louis- 
lana, it appears to be of minor importance as a cattle pest. In 
extensive collections made in Texas agents of this bureau have failed 
_ to find it in sufficient numbers to attract attention as a pest. In 
the vicinity of Hawthorn, Fla., however, it is the source of consid- 
erable annoyance to hunting dogs, and it has recently been found to 
be a pest of considerable importance to cattle and sheep in northern 
Tennessee. 
NATURAL CONTROL. 
Observations relating to natural enemies of this species are lacking. 
ARTIFICIAL CONTROL. 
Where hand picking is not sufficient to keep the species in control, 
mopping with one of the coal-tar products should be practiced. 
21448°—Bull. 106—12——6 
