186 LIFE HISTORY OF NORTH AMERICAN TICKS. 
The nymph (Tables LX XXV-LXXXVII).—The longevity of the 
nymphs of this tick is shorter than that of any other species of Der- 
macentor studied by us with the possible exception of those species 
which molt on the host. The records made indicate that during the 
hot summer months the longevity ranges between 40 and 60 days. 
The greatest longevity observed was between 76 and 108 days. This 
record was made in the fall months. These nymphs were kept in glass 
tubes with cotton stoppers on moist sand in the laboratory. It is 
probable that during cool weather a somewhat greater period of 
longevity would occur. 
Taste LXXXV.—Longevity of nymphs of Dermacentor occidentalis. 
. Number 
Date larvee molted to nymphs. Number. But on All larve dead. ama 
ost. ; 
1910. 1910. Days. 
JUNO RHSs ea dec eee e saci sees = cee beciceie 37 Onpduly 1S torAug. 42 °e 2-2. one 40-61. 
sj ebel:\y4 Loy ee eee Saode HOSES 18 0| Aug. 4 to Aug. 12...........-| 41-52. 
MOV YHa20 soccer tic den ecm icichee See 300 230 | Aug. 12 to Sept. 24.........- 23-69. 
Ly OCO PAM Sec aials wlale =m cee eeralcsa 4 0) ]) BeforeiOcti26 j- 5-2-2 -1--1- Less than 75. 
up. Viet. se Soee ese Se eee 1 Ol eceee CONS. cee sedsteeessccebene Less than 70. 
MP pip O=L0), ME as. sents cece ck 10 OF Nov.251t0. Dees 23 sac2.c een 76-108 
Taste LXXXVI.—Engorgement of nymphs of Dermacentor occidentalis. 
Nymphs dropped—days fol- a 
lowing application. num- 
gee gephe Host. eee ber | State of engorgement. 
Guinea pig....| (?) Sail SS lieed) eee oloaea meee |e cou ene 
shad GO aeescsaly oOUlesee loser [asics tidal | eal: xb lek 10 | One-fourth to fully. 
Bovine! is 2-8 718 beara ced (ea A | 1S Sse al sacs 1 | One-third. 
Rabbits aecccr 200! Pee aaka S208" | Sales. alee 72 | One-half to fully. 
Gninesipiess Gee le eases Diet eh ler A oak pr 2] Fully. 
1 These lots were accidental infestations, hence the exact date of attachment is not known. 
The shortest period of engorgement accurately observed was 4 days; 
the longest, 9 days. In the last instance the nymphs were still only 
about one-half engorged and were probably scratched off by the host. 
The weighted average engorgement period of all nymphs upon which 
accurate records were made is 5.56 days. Attachment was observed 
to take place, in most cases, almost immediately after the ticks had 
been placed on the host. 
