April, '13] BISHOPP AND KING: SPOTTED FEVER TICK 201 



the destruction of the adult ticks on the domestic animals, the deter- 

 mination of the period of activity of this stage is of importance. 

 The first appearance of the adults occurs shortl}' after the first warm 

 days of early spring. The date of appearance varies somewhat 

 according to the latitude, altitude, and, in a given locality, the climatic 

 conditions, particularly the temperature, have their influence. One 

 of the present authors (King) determined rather accurately the date 

 of first appearance of adults in the Bitter Root Valley in 1910 and 

 1911. March 11 and March 15, respectively, were the dates when the 

 first ticks were found during these years. The mean temperature at 

 Missoula, Mont., which is located near the mouth of the Bitter Root 

 Valley, was 43°F. or 8.2°F. above normal during March, 1910, and 

 39°F. or 4.1°F. above normal during Alarch, 1911. The minimum 

 temperature during March, 1910, was 21°F., while a minimum of 0°F. 

 was reached in March, 1911. At Hamilton, Mont., which is in the 

 center of the valley, the mean temperature for March, 1910, was 

 46.8°F. and for March, 1911, was 41.9°F. The much warmer March 

 experienced in 1910 than in 1911 no doubt explains the slightly earlier 

 appearance of ticks in 1910 than in 1911. We may also conclude that 

 the appearance of adults at a date earlier than March 11 must be 

 extremely rare as the winter of 1909-10 was not more severe than usual 

 and the March temperatures were much warmer than normal. 



At Rifle, Colorado, in 1910, ticks appeared shortly before March 

 23, while in 1911 they appeared between March 3 and March 14. 

 The temperature was considerably higher during the latter part of 

 February and during early March of the latter year. During 1911 

 the first appearance of adults was recorded in a number of different 

 sections as follows: Round Mountain, Nevada, about March 8; View- 

 point, Oregon, March 10; Weatherby, Oregon, March 14; Vernon, 

 Idaho, March 27; Buford, Wyo., about April 1. 



It appears that the zero of effective temperature of this species is 

 not far from 35°F. It is certain that this point is considerably lower 

 than in the case of insects and ticks which occur in southern latitudes. 

 The accumulated effective temperature (computed in daily units of 

 mean temperature) necessary to produce emergence from hibernation 

 is low, apparently being in the neighborhood of 37° F. Adults may 

 be expected to begin emerging within six to twelve days when the 

 daily mean ranges between 38°F. and 42°F. for several consecutive 

 days. The data at hand indicate that there is no active period between 

 the semi-active summer or aestivation period and hibernation. The 

 temperature at which dormancy is produced in the fall seems to be 

 about 10°F. to 15°F. higher than that producing emergence from hiber- 



