1916 ENTOMOLOGICAL SOCIETY. 113 



The only theory which all entomologists now agree upon is that the old idea 

 of the fly causing pain is wrong, seeing that it has no organs capable of piercing 

 the skin. Some authors claim that other insects as well as Warble flies cause 

 cattle to " gad." 



This is also entirely wrong, and can be refuted in several ways. For instance, 

 I saw Tahanidce and other flies worrying the cattle this year long after the last 

 Warble fly had left, and did not see any of them stampeding. Besides as I have 

 pointed out cattle only run one or two at a time from other insects. They merely 

 show anger and not fear, when they run into the bushes or dust themselves. 

 AVith H. hovis the fear is undoubtedly contagious. The only time I think it is 

 permissible to make a mistake, is when cattle are at play, when they often run 

 with their tails up. Or when, for instance, a steer has been roughly handled 

 and dashes wdldly into the middle of a herd of cattle, then one sometimes sees 

 a stampede. In other words if a cow gets really frightened from any cause and 

 runs, then those near her will often follow, and the fear spreads. This is exactly 

 what takes place when an animal is chased by H. hovis. 



The great difference between H. hovis and H. Uneatum is in their effect upon 

 cattle and in their methods of oviposition. I have shown that H. Uneatum may 

 not even be felt when it lays its eggs while resting on an animal's foot or on the 

 ground. When it does grasp the hairs to lay eggs for instance on the hock, it 

 does so gently, otherwise it would be brushed off before it had time to lay several 

 eggs on the same hair. 



H. hovis is rougher and clumsier in its attack and as it only lays one egg 

 at a time, it can do so regardless of the fact that the animal may be kicking or 

 running. 



The Penetration of the Skin, and the Lesions Produced by the Larva 



OF Hypoderma hovis. 



Hewitt (1914) saw three larva of 11. hovis work their way into the skin 

 of a calf. I have not been fortunate in seeing the penetration of the skin by 

 these larvae, but can confirm Hewitt's observation in another way, by showing 

 lesions on the skin of cattle, over which were found the eggs of H. hovis. 



I have already described the skin lesions produced by the larvae of H. Uneatum, 

 and of the disease caused by them, for which the name of hj/podermaJ rash was 

 proposed. The penetration of the larvae was proved in three different ways — ^by 

 removing bits of skin from cattle and placing larvae upon them, by finding a larva 

 in the act of passing into the skin of a cow, and finally by expressing two larvae 

 from the skin of an animal which I had under observation. The passage of 

 the larva in H. hovis was proved by cutting circles in the hair round new laid 

 eggs, and later, after the eggs had hatched finding the swellings underneath. 



The swellings are somewhat different from those caused by //. Uneatnm, 

 There is not so much exudation of serum, and they seem rounder and more raised. 

 They are usually about half an inch across, but if several eggs are laid close 

 together the swellings may merge. The explanation of the difference in the 

 character of these lesions, is because in H. hovis the eggs are laid singly. In 

 H. Uneatum. it is most likely that several larvae choose the same follicle for 

 entrance, seeing that a number of eggs are attached to the same hair. In my 

 experiments I also noted that the eggs nearest the skin hatched first, due no 

 doubt to the animal heat and to their having been laid first, and it would appear 

 probable that the larvre follow one another through the same opening. The result 



