THE CATTLE GRUBS OR OX WARBLES 87 
The construction of sheds is advisable where they will perform 
the double service of protecting the stock against heel flies and from 
adverse climatic conditions. 
REPELLENTS AGAINST HEEL FLIES 
For many years various ill-smelling applications have been used 
_ with the view of protecting cattle from the attack of heel or warble 
 fiies. Prior to the last few years, during which our knowledge of 
_ the life history of these pests has clearly showed that the eggs are 
_not deposited on the backs of the cattle, it was the custom to use 
\ yarious repellent smears and washes upon the backs of cattle. As 
it is now known that the eggs are deposited largely on the legs and 
_ lower portions of the body, the futility of this practice is at once 
_ evident. Inquiry into the results of the application of fly sprays 
_ has led the writers to conclude that the claims that they are efficient 
_ against grubs are unfounded. 
The fact that the adults of Hypoderma do not partake of food 
would suggest that their reaction toward attractant and repellent 
. chemicals or other substances would be less than in those species 
» which have the senses developed to aid them in finding food or breed- 
'ing places. The writers’ experiments and observations along this 
' line seem to bear out this conclusion. It appears probable that the 
| application on the animals of materials which tend to cover the hair 
or mat it together may affect oviposition more than those materials 
possessing various odors supposed to be repellent. The experiments 
/ in this field, however, have not been sufficiently extensive to enable 
| final conclusions to be drawn. 
During 1919 a dairy herd of 61 animals was used in tests of the 
_ application of repellents and solvent solutions, as follows: 2 per cent 
- compound solution of cresol, 10 per cent solution of acetic acid, un- 
diluted fuel oil (petroleum), and a mixture of 1 gallon of fish oil 
_ with 1 pint of commercial pine tar. These materials were applied 
to the legs of cattle, some with a spray pump and others with a 
brush. The applications were made at about 4-day intervals during 
the period when heel flies were active. While the treatments were 
| being administered heel-fly eggs were found on several of the treated 
animals. Some were even present on the legs of those treated with 
petroleum, and on those treated with a mixture of fish oil and pine 
tar. 
Observations made incidentally in the experiments discussed under 
“ Destruction of eggs or larvee by the use of wading vats” indicate 
that the application of 2 per cent coal-tar creosote dips at 4-day in- 
tervals has no marked effect in repelling flies. The same is true of 
wading-vat experiments with arsenical solutions. 
On a number of occasions where cattle waded and got their feet 
and legs well covered with mud the flies were found to deposit their 
eggs Ireely on the legs above it. The application of gummy mate- 
vials to the entire animal has not been tried, but this would hardly 
seem feasible from a practical viewpoint. 
DESTRUCTION OF EGGS OR LARV BY THE USE OF WADING VATS 
The fact that a considerable percentage of the eggs of Hypoderma 
are laid on the lower legs at once suggests the possibility of destroy- 
