﻿THE CATTLE GRUBS OR OX WARBLES 63 



■was greatly reduced in the middle of the day, increasing again in 

 the middle of the afternoon. 



The number of larvse recorded as dropping in the earlier morn- 

 ing hours is undoubtedly too small, as fewer examinations were 

 made between 8 and 9 a. m. than in later periods, and a much 

 smaller number still between 7 and 8 a. m. It is believed, how- 

 ever, that by adding all of those which may have dropped between 

 7 and 9 a. m. the total would not nearly equal the number which 

 dropped between 9 and 10 a. m. Of the 269 larvae the hour of 

 emergence of which was noted with considerable accuracy, 140, or 

 52 per cent, left the host between 8 a. m. and noon, and 129, or 48 

 per cent, between noon and 6 p. m. There is undoubtedly a greater 

 disparity than these percentages indicate, as the number of hours 

 in the forenoon period was smaller than the number in the after- 

 noon. Also, as stated above, some warbles that dropped in the 

 early morning hours were not recorded. 



The percentage of grubs dropping in the night was compara- 

 tively small. Considering the entire 392 larvae upon which 

 the writers have records, only 88, or 22.4 per cent, dropped out 

 during the 12 hours from 6 p. m. to 7 a. m. As a matter of fact, 

 this percentage is too high, as in it are included larvae which on 

 several occasions were found to have dropped from animals when 

 they were first examined in the morning; sometimes this examina- 

 tion being made as late as 8 or 9 o'clock. 



From their observations and the study of the data accumulated 

 the writers are led to believe that the activity of the host has 

 much to do with the dropping of the larvae. Feeding of the 

 animals usually took place between 8 and 9 a. m. and up to about 

 that time the animals were comparatively quiet, usually lying- 

 down. In the noon period following the morning feeding they 

 again became quiet and lay down much of the time, until 4 or 

 5 p. m., when feeding again took place. Just how activity of the 

 host should influence the dropping of the larvae it is not easy 

 to see. Possibly the muscular movements stimulate them. There 

 is a possibility also that the warming up of the back of the 

 animals by the sun following the cool night may tend to stimulate 

 dropping. In the instances cited by Glaser it appears that feeding 

 took place very early in the morning and hence his observations 

 may tend to substantiate this hypothesis. 



DISTRIBUTION OF THE LARV^ ON THE BACKS OP CATTLE 



As is well known, the larva* occur in the greatest numbers along 

 each side of the spinous processes from the shoulder to the hip bones. 

 In diagraming the backs of hundreds of cattle the writers have 

 observed that this distribution is veiy irregular, sometimes several 

 larvae being in one group and the rest of the back comparatively 

 free, while in other cases they are widely scattered over the entire 

 area. It seems certain, however, tliat this is simply a matter of 

 chance. In summarizing tlieii- figures on the distribution of (he 

 lai-vse the writers find that ahout MJ per cent of them occur in the 

 region of the dorsal vert('l)rii' and the other .^O per cent in tlic 

 lumbar region. As a rule they are iriore concentrated in the ai-ea 

 over the last three ribs. Although it is not unusual to lind grubs on 



