;")(> Oh.<iervcttions on the Hahitfi of Certai7i Flies 



The adoption of the second method cuts nearer the root of the evil, 

 and where suitable sanitary arrangements or efficient larvicides are 

 available much more effective work can be done even in summer. 



But, provided that suitable methods are forthcoming, winter would 

 probably be the best season in which to attack the problem. The num- 

 bers of flies have then been reduced by natural deaths, the ravages of 

 Empusa muscae and of HymenojDterous parasites, and carnivorous larvae 

 are still taking their toll. 



Portchinsky (1913) considers that the larvae of M. siabtdans and of 

 H. dentijjes wreak untold havoc amongst the larvae of M. domestica. 

 Graham-Smith (1916) thinks that he failed to bring the larvae of M. 

 domestica through the winter of 1914-15 because those, which survived 

 heavy rain, were destroyed by the larvae of H. dentipes, the progeny 

 of a single female, which accidentally gained access to the breeding 

 cage. 



In view of supplementing the work of Nature by artificial means, it 

 is important to discover where and in what stage, or stages, the insect 

 passes the winter. 



The writers on hibernation may be divided into four groups: Group I 

 which holds the opinion that M. do^nestica passes the winter in the adult 

 stage; Group II which considers that, though the adults which survive 

 the winter are the most important factor in perpetuating the species, it 

 is possible, but not sufficiently proved, that the pupal stage also survives; 

 Group III which recognises that some adults do undoubtedly over- 

 winter in suitable situations, but consider that the immature stages are 

 of most importance in the continuance of the species in the following 

 year; and, finally. Group IV which believes that M. dowestica hibernates 

 only in the pupal stage. 



In Group I appear Newstead (1909) and Hewitt (1914 and 1915). The 

 former (1907) wrote that, while the adults were found in the dwellings of 

 man throughout the winter and in early spring, "Whether they pass the 

 winter entirely in this stage one has not been able to ascertain. It is 

 highly jjrobable, however, that some of the pupae may remain over the 

 winter and hatch in the following spring." But as a result of a single 

 ox])erimcnt. carried out in October 1907, the same observer (1909) con- 

 cluded that the house-fly did not pass the winter in the larval or pupal 

 stages — "so that as far as one can trace at the present moment, the 

 only stage in the life cycle, which is found duiing the winter months is 

 that of the adult flies." Hewitt (1912) considers that "it is not unlikely 

 that larvae of Fannia canicularis, which developed late in the season, pass 



