224 EXPERIMENTAL 'FARMS 



2 GEORGE V^ A. 1912 



enormous tax on farmers, stock raisers and tanners. Their presence entails 

 the following: loss of flesh in beef and milk cattle, reduction in the milk 

 producing power and other strains on dairy cows and very great loss in the manu- 

 facture of the hides owing to the presence in them of the holes made by the maggots. 

 I am informed that it is customary to deduct two dollars from the value of every steer 

 on account of warbles. Thirty years ago it was estimated that the annual loss in the 

 United States caused by the warble fly was about ninety million dollars. Yearlings 

 and heifers suffer most from the attacks of this insect. It is undoubtedly one of the 

 most serious insect pests attacking cattle and at the same time one that is difficult 

 to control. The ' warbles ' are tumours caused by the larvae or ' maggots ' of the 

 warble fly. The larva sets up irritation beneath the skin with the consequent pro- 

 duction of pus and blood upon which it feeds. The warble flies are abundant during 

 the summer and fly in the fields from June to the end of August. They are about 

 half an inch long and covered with hairs like a bumble bee, the hairs being black, 

 white and yellow or reddish brown. They fly in the bright sunshine but do not bite 

 or sting which makes all the more remarkable the fact that their presence will cause 

 cattle to stampede and rush wildly about. The eggs are laid on the hairs of the 

 animals by the fly during the summer and are firmly attached to the hairs. It is 

 believed that most of the eggs are laid on the legs and heels of the cattle and rarely 

 on the backs and sides. How the maggot reaches its final position beneath the skin 

 has not been determined with certainty. It may either bore straight into the skin or 

 it may be licked into the mouth and from there work its way through the tissues to 

 reach its final position beneath the skin. Prof. Carpenter, of Dublin, Ireland, who for 

 six years has been conducting experiments on this insect and its method of control * 

 has found young maggots imbedded in the tissues of the gullet of* young cattle 

 slaughtered in August and October. Strosef has found that in the case of Hypoderma 

 hovis, which probably does not occur in North America, some of the larvse 

 probably enter the body through the skin. He also found that the full-grown larva? 

 leave the host chiefly during the night and early morning. By whatever way the 

 maggots gain entrance they finally arrive beneath the skin on the backs of the animals 

 about February and then give rise to the ' warbles.' When the maggots are wander- 

 ing through the tissues before reaching the back they are smooth but having arrived 

 beneath the hide they moult and become spiny. A hole is now made in the warble 

 through which the maggot breathes by means of two openings or spiracles at its tail 

 end. The maggot becomes full grown about the end of April or beginning of May 

 (in Eastern Canada) being now about an inch long. The ' ripe ' maggot works its 

 way out of the warble and falls to the ground where its skin hardens to form a brown- 

 ish black case or puparium from which the fly escapes in about four to six weeks. 



Remedial Measures. — It was formerly thought, and the belief is still widely pre- 

 valent, that the flies could be deterred from depositing their eggs on the backs of 

 cattle if various dips and smears were applied during the summer months. Prof. 

 Carpenter's investigations have shown that no reliance can be placed on such supposed 

 preventives. Nevertheless there is much evidence to show that the systematic des- 

 truction of the maggots in the spring before they leave the warbles is productive of 

 very beneficial results. It will be readily understood, that if the maggots are thus 

 destroyed in all the herds throughout a whole district, the number of warble flies will 

 be considerably reduced. Co-operation is necessary. In Denmark ||, this method has 

 been adopted with considerable success and co-operation in the systematic destruction 

 of the maggots has resulted in a marked decrease in the prevalence of warbles in thr.^o 

 districts in which the work has I een carried on. There is no doubt that, if this work 



* Journ. Dept. Techn. Insir., Ireland, Vol. 8, pp. 227-21G, Vol. 9, pp. 4G5-476 & Vol. 10, pp. 

 642-650 (1910). 



t.lrb. K. Gesundhl.taml. Wl. 34, pp. 41-76 4 figs. 1910. 

 Bulletin de hi Sociiti Nationale d' Agriculture, Xos. 3 & 6, 1!;10. 



