68 LIFE HISTORY OF NORTH AMERICAN TICKS, 
Taste XIII.—Summary of parasitic periods of Ornithodoros megnini. 
Larvee. Nymphs. 
First molted. Last molted. First dropped. | Last dropped. Total 
Tnfesta- a | para- 
tion. : ~.4| Para- : ? sitic 
: | Period Period| “.:;; Period Period i 
Attached. follow- follow- pe follow- follow- aes 
Date. |ingat-| Date. | ing at- Pp ‘| Date. jingat-| Date. ing 
tach- tach- tach- molt- 
ment. ment. ment. ing. 
1907. 1907. Days. 1907. Days. | Days. 1907. Days. 1908. Days. | Days. 
cca wee Aug. 31} Sept. 8 8 | Sept. 9 9| 8-9 | Oct. 4 34 | Mar. 27 201 209 
Biel Sietniaieis Oct. 13} Oct. 21 8 | Oct. 25 12] 812] Dec. 3 51 | Jan. 14 85 93 
1908. 1908. 1908. 1908. 
Be Age Apr. 7] Apr. 14 7 | Apr. 15 8| 7-8 | May 8 31} Oct. 2 171 178 
We Seer July 2] July 12 10 | July 14 12 | 10-12 | Sept. 24 53 |) Oct. 121 59 69 
1909. 1909. 1909. 1909. 1909. 
Det asst June 10} July 18 | 8 | July 19 9) 89 | Aug. 6 Dae OCs ah 105 113 
| | 
13 at tached. 
LIFE CYCLE. 
The larva may live under favorable conditions for 80 days. Upon 
gaining access to the ear they attach on the inside in the fold of the 
concha and even in the meatus, engorge, and molt in from 7 to 12 
days. The nymphs engorge more slowly and digest blood as they 
develop. They may leave the host as soon as 31 days after molting 
or may remain for 201 days and probably longer. Upon leaving the 
host they usually crawl up several feet from the ground and secrete 
themselves in dry cracks and crevices. Here they molt, are fer- 
tilized, and deposit eggs. The incubation period in summer has been 
as short as 10 days. An effective temperature of at least 412° F. 
appears to be required for embryonic development. Unlike other 
ticks, this species never engorges blood in the adult stage. 
The larve and more especially the nymphs are to be found on the 
host at all seasons of the year, although their seasonal abundance 
varies somewhat with local climatic conditions. 
ECONOMIC IMPORTANCE. 
This tick is undoubtedly of much more importance economically 
than is generally supposed. It is the source of great irritation to the 
host as evidenced by frequent and repeated shaking of the head. 
Townsend (1893) states that horses when badly infested have been 
known to roll as well. It is particularly injurious to calves which, 
unless treated and the ticks removed from their ears, frequently die 
as a result of the irritation. In some cases they run about shaking 
and rubbing the ears until exhausted. The milk yield of dairy 
cattle is undoubtedly lessened and in beef cattle the gain in weight 
correspondingly affected. On the range in the worst infested dis- 
tricts the loss of many head of cattle is chargeable to this tick. The 
deaths occur mainly during the winter and early spring, particularly 
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