196 [J'in«' 



Carpenter, G. H. ; Hewitt, T. R. ; Reddin, T. K. ; " The Warble-flies : 

 FoPRTH Report on Experiments and Observations as to Life-History and 

 Treatment." Irish Dep. Agric. Journal, Vol. 15, No. 1, pp. 105-132, 1914. 



It is an old-standing question how the larvae of the ox-warble flies {Hypo- 

 derma ) reach their situation in the " warbles " or abscesses under the skin of 

 the backs of cattle. The matter is of biological interest and of practical 

 importance. It has been thought that the flies laid their eggs directly on the 

 cattle's backs, and that the new-hatched larvae bored their way in directly 

 through the skin. Later, it was observed that the flies seemed to oviposit not 

 on the backs but on the legs, and as second-stage larvae were frequently found in 

 the walls of the beasts' gullets, it was supposed that the cattle licked the eggs 

 into their mouths, and that the larvae made their way through the gullet-wall 

 and wandered till they reached their final situation under the skin of the back. 

 For some years experiments on calves have been carried on in Ireland, and this 

 fourth report indicates that the first supposition is quite erroneous, while the 

 second, though nearer the truth, is not entirely coi'rect. 



The flies lay their eggs almost exclusively on the legs of the cattle, prefer- 

 ably on the hock-joint of the hind-legs. H. lineatum lays its eggs in rows, a 

 number on a single hair. H. bovis lays them singly and quickly, and causes the 

 cattle to get very excited. Merely touching them with a stick on the parts 

 chosen by the fly causes thein to gad in a similar manner, whereas touches on 

 the back create no excitement, and even the.blood-sucking of Haematopota only 

 makes them shake their skin. 



Carpenter and Hewitt have already described the reproductive organs and 

 first-stage larvae of the flies (Sci. Proc. R. Dublin Soc, Vol. 14, pp. 268-289, 

 pi. 21-26, April, 1914). Tlce maggots bore in through the skin of the part of the 

 body 071 which they are hoAched, i.e., the legs ; this was actually observed in one 

 case, and the entrance-holes were found in many. That the maggots reach the 

 wall of the gullet by being licked into the mouth appears, therefore, almost 

 disproved ; experiments, which at one time seemed to support this idea, have. 

 by continuance over a longer period, negatived it. But reseach on this point 

 is still in progress. 



The wanderings of the first-stage larvae after piercing the skin have not 

 been followed. But the second-stage larvae are quite regularly found in the 

 sub-mucous layer of the gullet- wall. They commence to appear there about 

 August, their maximum numbers are reached in November, and by February or 

 March they have disappeared from this part of the host's anatomy. During the 

 later part of the time thej' are found further back towards the stomach, and a 

 few have been discovered just outside the muscular coat of the gullet. Possibly 

 they pass upwards to the back via the diaphragm. As is ^vell known, the life- 

 cycle is completed by the larvae becoming mature in the " warbles " on the backs 

 of the cattle during spring and summei-, and by their quitting the warbles when 

 full-grown, and falling to the ground, where they pupate. 



The facts of the files ovipositing on the legs, and of the second-stage lai'vae 

 appearing in the gvdlet-wall, have received confirmation by (inter alia) experi- 



