FORMS INJURIOUS TO HUMAN INDUSTRIES 



349 



Domesticated animals are attaclN;ed by a great variety of 

 insects, of which only a few can be here mentioned. Some- 

 thing has elsewhere been said about Bot-Flies (see p. 191). 

 Two such forms, the Ox- Warble Flies [^Hypoderma bovis and 

 H. lineatus, fig. 1245), lay their eggs on the legs of cattle, 

 usually near the heels. It is probable (but not absolutely cer- 

 tain) that the maggots when hatched pierce the skin, under 

 which they make their way to the back. At any rate they are 

 found in that region later on, living in swellings ("warbles") 

 which open to the exterior. Of the injuries inflicted Somerville 

 says (in Farm and Gar- 

 den Insects) : — " The 

 damage done by this 

 insect is enormous, the 

 Newcastle Hide Pro- 

 tection Society, for in- 

 stance, reporting that 

 the hides dealt with in 

 that town alone in 1892 

 had been damaged by 

 warbles to the extent 

 of ^14,000. Besides 

 the injury to the leather 

 H. bovis causes great 

 damage by unsettling 

 cattle and preventing them thriving properly. When cattle dis- 

 cover that the fly is hovering near they rush wildly about the 

 field; and the constant irritation to which the larva subjects 

 them when located in the skin is no less detrimental to the ani- 

 mals. The flesh in the neighbourhood of the warbles is also 

 much reduced in value, being covered by a jelly-like substance 

 known as 'licked beef." 



The bite of the much-dreaded Tsetse Fly {Glossina viorsitans) 

 of tropical Africa is fatal to horses, producing " nagana " or " fly- 

 sickness " (see p. 241). This is because the bite introduces into 

 the horse's blood certain stages in the life-history of a parasitic 

 animalcule [Trypanosoma), which attacks the red corpuscles. 

 Other biting flies may introduce fatal germs, as, e.g., the bacilli 

 which are the cause of anthrax (splenic fever, quarter evil). 



The insect pests which damage stock are mosdy Flies and 



Fig. 1245. — Ox-Warble Fly [Hypodcrjiin), enlarged 



