INSECTS INJURIOUS TO CATTLE 4O7 



The horn fly deposits eggs preferably in soft or 

 moist manure, but will also lay them in decaying veg- 

 etable matter. In about 24 hours, dependent more or 

 less on temperature, they hatch out. The larv^ then 

 live near the surface of the earth and in about 15 days 

 emerge as flies. The life of the common fly is not greatly 

 different. Both multiply with amazing rapidity, and, 

 doubtless, are usually harmful in proportion to their 

 numbers. 



The season for flies varies in duration with varia- 

 tions in normal temperatures. The longer and the more 

 intense the period of summer heat, the more favorable is 

 it for the continuance and prolongation of the season 

 for the flies. Flies come with the advent of settled 

 warm weather and remain until the season of the 

 earliest frosts. In the northern states, they usually be- 

 come troublesome in the latter part of June. South- 

 ward they appear earlier with decrease in latitude, and 

 northward later with increase in the same. The period 

 of fly invasion, therefore, covers from three to more than 

 five months. 



Flies are harmful to cattle in various ways. They lay 

 eggs in wounds, not protected, which produce maggots 

 and may become the carriers of disease, as in the case 

 of malignant anthrax. But the chief loss from flies 

 comes from the unrest which they occasion. This un- 

 rest, it is generally believed, lowers the milk yield in 

 cows and is antagonistic to the laying on of flesh in 

 other cattle. The horn fly injures by its bite, which is 

 in the nature of a sting. While common flies do not 

 sting, it is evident that their presence produces discom- 

 fort by the way in which cattle try to dislodge them by 

 striking with head and tail. It is reasonable to suppose 

 that in proportion as they are present, they would hinder 

 production in the fly season. But experiments con- 

 ducted by some of the experiment stations to protect 

 cows in milk from flies showed what may be termed only 



