100 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE 
In the writers’ experience they have found that grubs may be ex- | 
tracted at any time during the course of their development in the 
backs of the cattle. They have found that, by removing the small 
scabs which usually develop around the apertures cut by the young 
or third-stage larvee, they can be pressed out with great ease. There 
seems to be a period in the fourth stage during which extraction is 
more difficult. By using care, however, practically every grub can 
be removed by hand. (Fig. 36.) 
lig. 36.—Extracting Hypoderma larva from cow by pressing down around cyst 
opening 
There is a very marked difference in the ease with which grubs 
may be etxracted from the backs of cattle of different breeds. In 
the case of the island breeds the skin appears more flexible and 
elastic, and extraction 1s comparatively easy. Very often with the 
Holstein-Friesian and certain beef breeds it is almost impossible to 
squeeze the grubs out by hand. The condition of fiesh of the host 
also has a considerable effect on the ease of extraction. Very poor 
or extremely fat cattle are more difficult to treat than those in fair 
condition. 
The method of procedure in extracting grubs may be modified to 
suit the individual and also the character of the skin of the host 
under treatment. Inexperienced people often find extraction ex- 
tremely difficult; but those who have considerable experience are able 
to remove the grubs with comparative ease, and they seldom break 
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