540 Observations on Habits and Parasites of Common Flies 
21. The activities of flies are more influenced by temperature than 
by any other weather condition (p. 497). They tend to be most active 
in bright sunshine, are inactive in dull weather, except in the warmer 
months, and are very sensitive to wind, rain and great heat. 
22. The larvae of H. dentipes and certain other species devour 
other fly larvae and destroy great numbers. Such carnivorous larvae 
must be extremely important agents in limiting the numbers of many 
species likely to carry pathogenic bacteria to human food. 
23. The burial of carcases does not prevent the development of 
the larvae present on them, or the subsequent emergence of the flies. 
24. Taking into consideration the extent to which wasps visit 
fruit, whether on trees or exposed for sale in shops, their well-known 
partiality for jam and other foods, their liking for excrement, decaying 
animal matter and flies it seems very probable that they act not 
infrequently as agents in disseminating pathogenic and putrefactive 
bacteria. 
25. Contact with infected adults of M. domestica is not essential 
in the transmission of empusa disease. C. erythrocephala, H. dentipes 
and F. canicidaris occasionally die of this disease, and may be agents 
in transmitting it to M. domestica. 
26. Mites of different species attach themselves to flies, and may 
remain clinging to them for several days. Certain observations show 
that they may act as carriers of nematode worms. 
27. The pseudo-scorpion, C. nodosus, was found clinging to flies 
of several species, and two examples of C. scorpioides were found on 
a specimen of S. calcitrans. These creatures may remain attached to 
flies for several days. 
28. The braconids, A. manducator and A. cephalotes, pass the winter 
as larvae in the puparia of C. erythrocephala and other flies. Some of 
the males and females of the former species emerge in the spring, but 
the majority do not emerge till the autumn. A. manducator destroys 
very large numbers of fly pupae, and in this respect seems to be a most 
beneficial parasite. 
29. In these experiments a chalcid, M. acasta, parasitised great 
numbers of blow-fly puparia already containing larvae of A. manducator. 
This chalcid seems to avoid shady places. A few pupae were parasitised 
by other chalcids. M. acasta and the other chalcids hibernate as 
larvae in the fly puparia. 
