DIPTEKA OK TRUE FLIES. 235 



it becomes banded with prickles, which cause irritation and 

 inflammation of the immediate surrounding parts, and thus 

 the swelling or " warble '' is produced. We notice these out- 

 ward signs of attack coming about January. The inflammation 

 set up by the bot produces matter, which eventually causes the 

 warble to burst at the top, a small round orifice appearing. 

 The "bot" lies beneath this, in a cell formed in the hypodermal 

 tissues, and when full grown squeezes its way out and falls to 

 the ground, where, wriggling under some tuft of grass or stone, 

 it pupates in its old larval skin. H. lineata is much like H. 

 bovis, but somewhat smaller. 



The small maggots on hatching enter the skin and wander 

 about until they eventually reach the back or flank. At one 

 time they were supposed to be licked up by the cattle and enter 

 via the mouth, but Carpenter has recently shown that muzzled 

 calves become parasitised. 



Prevention and Treatment. — Smearing the back and loins of 

 beasts with some greasy substance, such as cart -grease and 

 paraffin, was recommended. As the flies lay their eggs on the 

 legs it is not surprising that this did little good. Smearing the 

 legs and flanks, however, is likely to be beneficial. As Warble- 

 flies are very susceptible to changes of temperature, and will 

 not enter shade or pass over water, giving the cattle shelter 

 either of trees or rough hovels in the meadows, or turning them 

 where they can run to water for protection, is advisable. 

 Eemedial measures consist of destroying or extracting the larva 

 from the warble. Mercurial' ointment is one remedy ; a small 

 piece rubbed into the warble when it has just opened will soon 

 destroy the grub, and allow the wound to heal up. Not only 

 does the ointment kill the larva by blocking up the air-pores or 

 spiracles, but it destroys the grub in the cell ; but it should not 

 be used in great quantities. Cart-grease and M'Dougall's smear 

 have similar effects, but are not nearly so certain in results. 

 There is nothing like the old plan of squeezing out the maggot 

 and killing it at once, before the warble has become too old. 



