78 BULLETIN 1369, U. 8. DEPARTMENT OF AGRICULTURE 
The time of maximum abundance of larve in the backs of cattle © 
varies considerably in different herds and during different years. At — 
Dallas, Tex., this maximum usually occurs, on the average, about 
January 10, and at Uvalde, Tex., about December 15. 
The date when the last grub leaves the cattle varies considerably 
in different herds, as well as in different localities and during a 
series of years. This point is of little economic importance for ZH. 
lineatum in those States where H. bovis also occurs, for the latter 
always persists in the hosts later in the season, and the two species 
must be dealt with asa unit. At Dallas, Tex., the date when cattle 
become free from grubs in their backs has been determined during 
several years. In 1915 this date was March 20; in 1916, April 12; 
in 1917, March 18; in 1919, March 15; in 1921, March 20; and in 
1922, March 16. At Uvalde, Tex., Mr. Parman has observed the 
cattle to become free of grubs between January 20 and April 12. It 
is interesting to note that Mr. Babcock found two specimens of 
HT. lineatum in the back of a cow at San Angelo, Tex., on March 20, 
1924. These larvee would not have been mature in less than 15 days. 
Since the grubs of this generation began to appear in the backs of 
cattle in that region about August 2, there is a remarkable and very 
unusual period of infestation of the backs of cattle of about eight 
months. Thus it appears that there is a wider variation from year 
to year in this respect in southwestern Texas than occurs elsewhere. 
A very general idea of the time when all larve of H. lineatum 
have emerged from the cattle may be gained from the following 
dates: March 1, southern Arizona and southern California; March 
15, Alabama, Georgia, North Carolina, Oklahoma, and southern New 
Mexico; April 15, Maryland, Missouri, and Nevada; May 1, Penn- 
sylvania, Indiana, Colorado, Idaho, and Washington; June 1, North 
Dakota and Michigan; June 15, New York and Montana. Observa- 
tions made by W. E. Dove in 1924 indicate that all larve of Z. 
lineatum would have left the cattle in the vicinity of Aberdeen, 
S. Dak., about May 5, and at Minot and Dickinson, N. Dak., and at 
Moorhead, Minn., about May 10. The season, however, was more 
advanced that spring than usual. On May 1, 1924, all grubs were 
found to have emerged from cattle at Sioux Falls, S. Dak. 
In general the duration of the infestation of the backs of cattle 
in H. bovis is longer than in H. lineatum. This is brought about 
through the longer developmental period of the larve in this situa- 
tion and the wider spread of time between the date the first larvae of 
fT. bovis reach the back and the date the last ones appear there. 
The writers’ records indicate that the earliest larve of H. bovis reach 
the subcutaneous tissues from one to two weeks after those of Z. 
lineatum. On the other hand, the larve of H. lineatum arrive in 
that portion of the host in much larger numbers proportionately 
during the first month or six weeks following their first appearance. 
The writers have checked closely the earliest appearance of larvee 
of H. bovis in the subdermal tissues, as well as the time of dropping 
of the last grubs in herds of cattle in New York during three seasons. 
The earhest appearance of H. bovis was February 2 in 1923 in 
Orange County, N. Y. In 1920 they appeared about February 26, 
and in 1922 about February 22. At Herkimer they first reached the 
subdermal tissues about March 8 in 1920, April 15 in 1921, and 
