234 
THE LIFE-HISTOEY OF DERMACENTOR 
VARIABILIS\ 
By SEYMOUR HADWEN, D.V.Sci., 
Assistant Pathologist, Dominion Department of Agriculture, 
Agassiz, B.C. 
During the past three years I have made various attempts to raise 
Dermacentor variahilis through its various stages on tame rabbits and 
have at last been successful.- Though there are still many points con¬ 
nected with the life-history to clear up, it is at any rate the first step 
towards finding ways and means for its control. 
To the total of ISO'S days it is necessary to add ten days at 
each stage for the hardening, of the skin, which increases the total 
to 210'5 days, without taking into account the time occupied in waiting 
for a host. The period of ten days allowed for the hardening of the 
skin is about correct for the nymphs, as can be verified b}^ the table. 
Out of eleven nymphs put on a rabbit on May 9th, only one attached 
itself, but 13 of those put on May 13th gorged. 
Only twelve females and one male were recovered at the end of the 
experiment, showing that the conditions were adverse to their develop¬ 
ment. In the first place, the larvae were starved from August 25th, 
1911 to February 10th, 1912, a period of five-and-a-half months. 
Secondly, the temperature at which they were kept was very variable; 
the nymphal moult being undoubtedly much prolonged on this account. 
The ticks were kept in unheated rooms the greater part of the time, and 
the only occasion on which they were kept at a really warm tempera¬ 
ture was when they were first put on to the rabbit. On this occasion 
they had been previously warmed and the cage and room were heated. 
In order to form an opinion as to the season of the year in which 
D. variahilis goes through its various stages, it is necessary to say a 
1 Dermacentor variahilis (Say, 18'21; Banks, 1907) = Dermacentor electus (Koch, 1844; 
Stiles, 1910). 
