162 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



Various methods are used to reduce the number of flies in 

 cow stables and in milk-houses. The cows are sprayed or 

 brushed with mixtures of drugs or chemicals known as fly 

 repellents. Sometimes sheets of fly-paper are placed about the 

 buildings. Milk-houses are very often screened and more rarely 

 stables are also screened. Fly repellents are only temporary 

 in their action and they are often objectionable on account of 

 their odor. Fly-paper is unsightly and inefficient. Fly-traps 

 are more useful. Screening milk-houses gives good results and 

 is desirable in all cases, but screening stables is not satisfactory. 

 Since the doors must be opened frequently and sometimes for 

 long periods to remove manure, to take in the feed, and to drive 

 the cows in and out, there is abundant opportunity for flies 

 to enter. The cow-fly or horn-fly is carried in on the cows. All 

 of these methods are fundamentally defective because none of 

 them prevents the breeding of flies. The most rational method 

 of attacking the fly problem is to remove or abolish, in so far as 

 is possible, the conditions which favor the development of the 

 insects. To do this intelligently it is necessary to consider their 

 habits and life history. 



Three varieties of flies are commonly found in cow stables : 

 the common house-fly, the cow-fly or horn-fly, and the stable- 

 fly or biting-fly. The house-fly and cow-fly are usually the most 

 numerous, but in some sections of the country, especially in the 

 grain belt, the stable-fly is present in large numbers. The dif- 

 ferent varieties can usually be distinguished by the part of the 

 cow which they occupy and by their sitting position. The small, 

 black cow-fly is generally located upon the back and sides of the 

 cow, and in rainy weather on the under parts of the body, sitting 

 with the head downward. The stable-fly usually occupies the 

 lower parts of the legs and nearly always sits with the head 

 upward, while the house-fly may be found on any part of the 

 cow and may sit in any position, but never with the head pressed 

 into the hair as though feeding. The stable-fly is about the 

 same size as the house-fly but has a more plump appearance 

 and has longitudinal lines on the thorax and several dark spots 

 on the abdomen. The horn-fly is smaller and black. 



The house-fly seems to prefer to deposit its eggs in horse 



