996 



The Warble Fly. 



[JAN., 



Description and Life of the Pest. — The egg-laying season lasts 

 from May until September, the smaller fly appearing first, and 

 the larger one or two months later. As may be seen from Fig. i, 

 the eggs are of a rather curious shape. They are about one- 

 twelfth of an inch long and each one has a grooved base by 

 which it is attached to the hair of the animal. The eggs are 

 laid by the female chiefly on the hind legs of the animal attacked 

 and usually just below the heel joint or hock, more rarely on 

 the flanks, and apparently never on the back. The larger fly, 

 H. bovis, lays her eggs singly near the base of a hair, but the 

 smaller one, H. lineata, places them in a row of seven or more 

 half-way up a hair. 



In four or five days the Httle maggots are hatched and at 

 once enter the skin close to where the eggs were laid. At this 

 stage the maggot is only one-thirtieth of an inch long, but it 

 has relatively very strong sharp jaws and spines. Having 

 bored into the skin the tiny maggots spend some time wandering 

 through the system of the animal until they finally reach the 

 wall of the gullet in which they are found embedded from 

 September to January. They are now in the second stage, 

 somewhat narrow and cylindrical, with feeble jaws and very 

 few spines. After several months' residence in the gullet wall 

 the maggots continue their wanderings and begin to appear 

 under the skin on the back of the animal, sometimes as early as 

 November and December, but much more frequently from 

 January onwards. Here they enter upon the third stage of 

 their existence ; they become larger, thicker, and more spiny 

 (Fig. 2). Each maggot lies in a small swelling, feeds on the 

 fluid which arises from the animal's inflamed flesh, and breathes 

 through a hole that is bored through the skin, the air openings 

 at the maggot's tail end being immediately under this hole. 



In late winter or early spring most of the maggots become 

 fully grown and afterwards work their way out through the 

 holes in the skin and fall to the ground. They have a large 

 number of tiny sharp spines arranged in rows on their bodies, 

 and these spines help their movements. Falling to the ground 

 the maggot undergoes a change, its outer coat becomes hard, 

 firm, and dark in colour (Fig. 3) ; for six weeks or so it remains 

 motionless among the grass, or under a stone or clod, the insect 

 being now in its resting or pupal stage. Then a round lid splits 

 off from the front end and the fly comes out. 



How to Destroy the Pest. — There is no evidence that the 

 various washes and smears commonly recommended for use in 

 summer are of any value in preventing flies from laying their 



