450 JocRN.Aj, OF TUh; l)i;i'AirjMi;M of Aokk uli uke. — Nov., 1922. 



reason that can be advanced to account for tliis is that further inland, 

 sheep purge much more than near the coast, and this pvirging makes 

 the wool so attractive to tlie flies that they l)low it at once. The 

 purging-, or diarrhoea, would appear to be due to the presence of 

 worms in the sheep, and for some reason sheep are more affected with 

 worms further inland than nearer the coast. There may also, of 

 course, be some possibility that the differences in altitude and distance 

 from the sea have some effect on the bionomics of the flies themselves, 

 but at the same time it should be mentioned that all three species 

 found infesting wool have been bred from meat exposed in East 

 London during- the present summer. 



Many more data are still required before the distribution and 

 prevalence of the various blow-flies in the Union can be fully known, 

 but as far as the writer's observations go at present, the two species 

 of Pycnosdma have proved to be a serious pest in wool only in the 

 coastal regions, while the Lucilia has only been bred in large 

 numbers from wool sent from the Orange Free State; that is to say, 

 as a pest it is more prevalent on the higher inland plateau than 

 the other two. 



As far as the infestation of sheep in the Border District is 

 concerned, there appear to be two more or less well-defined seasons 

 of abundance for the fly — in October and again about January- 

 Febrviary. The flies are, hoAvever, not absent in between, and the 

 reason for the apparent periodic abundance at these times may be 

 due to the fact that shearing takes place about TsTovember, hence 

 during- the hot weather the wool is long in October, and then again 

 towards the end of January. The flies are more troublesome when 

 the wool is long than when it is short. 



In connection with the work on the sheep blow-fly, experiments 

 have been carried out to identify the maggots of the various blow- 

 flies, particularly those infesting sheep. Pieces of meat were exposed 

 out of doors, and the resulting maggots isolated and reared. It is 

 interesting to note that so far the flies bred in this way are the same 

 as those reared from wool and from dead sheep, with the addition 

 of Sarcophaga liaem.oirhoidalis, the common grey flesh-fly. The last- 

 named fly has not been bred from sheep, and it seems to have a 

 greater preference to meat, materials such as soiled wool that are 

 attractive to the others not being much to its liking. 



The identification of the maggots of flies is rather intricate, 

 as in their grosser structure they are very like each other, 

 generally closely resembling the maggot of the house-fly. More 

 detailed examination of the maggots of various species of flies has 

 revealed certain structures by means of which it is possible to identify 

 them with a considerable degree of accviracy. In general, the form 

 of a maggot (Fig. 1) is broadest at the hind end, tapering towards 

 the head end, the body being divided into apparently twelve 

 segments ; there are no legs, and in the type of maggot under discus- 

 sion there is no clearly differentiated head. The skin is often 

 provided with minute teeth [Fig. 1 {d)~\ in bands or restricted to 

 limited areas on the ventral surface and which aid in progression; 

 some maggots have rows of projecting processes all over the body. 

 At the head end can be seen projecting a pair of black hooks, the 

 great hooks or mandibles [Fig. 1 (</)]; these are articulated to a 

 structure within the head end of the l)ody termed the 



