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. 
TaBLE LXXXI.—Engorgement of adults of Dermacentor venustus. 
| Females dropped engorged—days following | 
Date | ee application. Total 
females | Host. ae number 
applied. | : F dropped. 
| 8 9 10 11 12 13 14 17 
May 15,1908 | Bovine............... 2 ef sR 4 eg od GR Dc, a ay Be ied Dae Parr | 2 
June 15,1909 |..... Pt eee | ot ae Pet IE ge ke 1 eines A Lee 1 
Mar. 19,1910 | Guinea pig!.....--.-- uses 1h al ee | eee eo Hy Seve? 1 
Mar. 29,1910 |..... (OR See ee ee 1 US Peers Seer ee ae feeetios bate cet |. he 1 
fn, “aaee0 | BOVINE. .2 22. 2-...... MY atts Fel sae eat liers soe 2 a eee eee fc oe 4 
Apr. 13,1910 |..... PEE Eee Ae oe 1 oe See ee ee ee ee one ee) ee 2s ben cee 1 
Apr. 15,1910 | Guinea pig. ......-..- Ate ae cleanin 3 eens = NH eee ee alle [Sooo Pris 2 1 
Bray 48,1900 | Bovine.....-......... 3 Mich cay A S| eo ee Pmt de De tees hx bei. 3 
sry 26,1910 | Rabbit.........5..... ae ae tae Ned Oe) ek Poe bape 1 Mh Syl 3 1 
mar 204914 | Bovine. ..------<-.6.- Ve eee 5 ISOS. cee. S. | bee a RSE es 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 
