THE TROPICAL HORSE TICK. 203 
TaBLeE XCVII.—Summary of parasitic periods of Dermacentor nitens on a bovine. 
Days following application of larve. 
Date larvee applied. Location. Larve molted. Nymphs molted. | Females dropped. 
J Aji 10) ae Sadan eee eee Scrotum .. 13 15 24 29 Not fertilized. 
Uh Dee or ee ee ee pedo.2sek 9 16 17 26 29 38 
JIU 2 Eee See ee coe Ware 2 8 11 17 18 26 41 
LIFE CYCLE. 
The larve are short lived, living only 71 days in summer under the 
most favorable conditions; they engorge and molt on the host as 
soon as 8 days after attachment. Nymphs may molt as soon as the 
seventeenth day after attachment or 7 days after the larve molt. 
Adults may engorge and drop as soon as 9 days after the nymphal 
molt or 26 days after attachment as larve. In summer oviposition 
may commence on the fourth day following dropping and as many as 
3,392 eggs may be deposited. Eggs may hatch in 24 days during the 
summer. An effective temperature of 930° F. appears to be required 
for incubation. 
ECONOMIC IMPORTANCE. 
In the United States this tick has been found to be of considerable 
economic importance in the vicinity of Brownsville, Tex. In Novem- 
ber, 1907, one of the authors (Hooker) accémpanied by Mr. J. D. 
Mitchell visited the Carman Ranch, 7 or 8 miles north of Brownsville, 
where a dozen or more horses had been at pasture for a number of 
weeks. Several of these animals were lassoed and examined. Their 
ears were found to be literally filled with ticks of this species in all 
stages of development. The molted skins and excrement which had 
collected in the ears in large quantities were the source of a nau- 
seating stench. Bishopp observed similar conditions among horses, 
mules, and burros at Tampico and Victoria (Tamaulipas), Mexico, 
during December, 1909, all stages of the tick being present at that 
time. He was informed that this is a troublesome pest in that region. 
Work animals become “touchy” about the head and sometimes refuse 
to be bridled. Several men stated that the ears of animals fre- 
quently suppurate extensively and that in some cases the distal half 
of the ear drops off. 
Dr. N.S. Mayo, in the report of the Cuban Experiment Station for 
1907, page 25, says: ‘‘ These ticks sometimes collect in horses’ ears in 
such numbers as to cause the ears to lop and the screw-flies attack 
the ear and permanently disfigure the animal.” The filth and decay- 
