THE ROCKY MOUNTAIN SPOTTED-FEVER TICK. 179 
number of instances males have been observed to remain with females 
until the latter had become engorged and dropped, when they sought 
other mates. As many as three females have been seen to be fer- 
tilized by a single male. In many cases the females are nearly 
engorged before being visited by a male. Some of our observations 
indicate that the males usually start in search of mates in the early 
morning or late in the evening. Males have been observed to remain 
on a host for two months, at the end of which time they were removed. 
During this period two successive lots of females were applied and 
engorged, the males fertilizing both of them. 
The period of engorgement at Dallas, Tex., varied from 8 to 17 
days. After fertilization takes place engorgement appears in most 
cases to proceed more rapidly. 
TaBLeE LXXXI.—Engorgement of adults of Dermacentor venustus. 
Females dropped engorged—days following 
Date ran application. Total 
females Host. eer number 
applied. | ; dropped. 
| 8 Ce a FN a ee fe PM 
. | 
May 15,1908 | Bovine. ..-........-.. 2 Me leis See estes [aces (ee ecoe uae eee 1 2 
June 15,1909 |..... (Cee cae ee 7 Reet e ee coe) eee, | eee | ee | tie | ere ees 1 
Mar. 19,1910 | Guinea pig........... a | eaters: | essere gece alee sien eee espe | Sepa 1 
Mar. 29,1910 |..... (Clee Sense nes Aane 1 1 Reve ea ee |e ee ee 15 Sexes 1 
Apr 1,190 | Bovines---2---2---.-: AD eeecer see oe eeseee 2 Pd bee eatin ||, ease 4 
Apr. 13,1910 |..... (Gly Seeeese ae sees ee 1 UP Re es eee eee ere eso Smee 1 
Apr. 15,1910 | Guinea pig........... eee s | eee eee iL bes | eon ar epee | eer 1 
May. 4° 1910)|\ Bowine — 5.2 ace oe 3 Dye ed 1 eee 2 (en a Ly |< seach tex 3 
duly, 28; 19104) Rabbit.2 2). 220). Og] memes Stereos | erararerciall eager he sermtrees |i eve Ui gee a 1 
Mar. 29,1911 || Bovine. 4:..-.25.2...: 0 eee 5 Fe eee ee ee oan TD eee 7 
LIFE CYCLE. 
The larve have a longevity of about 2 months. They engorge in 
from 2 to 8 days after attaching to a host and may molt as soon as 
6 days after dropping, a total effective temperature of 272° F. being 
required for this molt. Nymphs may live for more than 300 days. 
They engorge in from 4 to 9 days after attaching to a host and they 
may molt as soon as the eleventh day after dropping, a total effective 
temperature of 485° F. being necessary to produce this transforma- 
tion. Adults have been observed to live for 413 days and since this 
record was made on ticks which were collected in the spring, they 
must have had a total longevity of about 600 days. Females may 
engorge as soon as 8 days after finding a host, commence depositing 
eggs as soon as the fifth day following dropping, and deposit as 
many as 7,396 eggs. Embryonic development may be completed in 
16 days, an effective temperature of 614° F. being required. 
It appears that the life cycle of this tick usually requires 2 years. 
The winter is spent in the unengorged nymphal and the unengorged 
adult stages. The adults begin to emerge from hibernation soon 
after the snow disappears. The great majority of them attach to 
