504 Observations on Habits and Parasites of Common Flies 
in buried carcases, and moreover that they are little, if at all, retarded 
in their development, since flies emerge at the same time from carcases 
buried while eggs only are present on them, and from half-eaten carcases 
containing large larvae. Further the larvae are able to make their 
way up through tightly packed earth to the neighbourhood of the 
surface, where they pupate. The burial of a carcase therefore does not 
prevent flies emerging from the eggs already laid, and only limits the pro¬ 
duction of flies by preventing later batches of eggs from being deposited. 
To illustrate the number of flies which may emerge from a carcase 
the following experiment may be quoted. The body of a medium 
sized guinea-pig was exposed for thirteen days, and then placed in an 
earthenware pipe and lightly covered with earth. Fourteen days later 
flies began to emerge. Altogether 2511 flies appeared, 1122 male and 
1059 female Lucilia, 182 male and 145 female C. erythrocephala, and 
3 0. leucostoma, some of which were normal in size, and others small, 
indicating that the food supply was not quite sufficient. 
It is probable that under natural conditions large numbers of larvae, 
which feed on animal matter, perish from lack of food. Numerous eggs 
were often noticed on the bodies of very young birds fallen from nests. 
Such bodies could only afford food for a very limited number of larvae. 
Larvae which do not die of hunger, but are underfed, produce 
small flies (see Graham-Smith, 1914, Plates xxv, xxvi). According to 
Griffith (1908) small specimens of M. domestica are sterile, but this is 
not the case in C. erythrocephala. The writer confined several newly 
emerged very small blow-flies of both sexes in a cage, and eggs were 
deposited from which blow-flies of normal dimensions were reared. 
Wasps. 
Up to the present no one seems to have pointed out that wasps, 
owing to their filthy habits, may be the carriers of pathogenic and 
putrefactive bacteria to articles of food. 
Wasps of the common species, V. vulgaris, V. sylvestris and F. 
germanica, were caught in traps placed over human excrement. Whether 
they were attracted to this material in order to feed on it, or to hunt 
the flies, which resort to it, is not quite clear, but contamination of 
their feet and jaws with such material was frequently noticed. 
They are also greatly attracted to decaying animal matter in all 
stages of decomposition. In carrying out investigations on the putre¬ 
faction of animal carcases, and the means of arresting the process, many 
bodies of large and small animals were exposed in an open field four 
