The common House-fly,Musca domestica, L., and its Behaviour to Temperature and Humidity

The study of the common house-fly,Musca domestica, L., has not received the attention it merits by medical entomologists. Although the correlation betweenfly-borne diseasesandclimatic factorshas interested several workers, this correlation has not been satisfactorily explained. An investigation of the influence ofclimatic factorson house-flies was therefore undertaken.House-flies can be reared in the laboratory by a proper choice of the breeding medium and suitable technique. Manures, kitchen refuse and synthetic media may be used but the last mentioned is recommended for the production of a supply of standard insects.M. domesticachooses the lower humidity on each of the humidity gradients, 20–40, 40–60, 60–80 and 80–100 per cent., at a constant temperature of 25°C. The choice is significant for both sexes, and for dry and wet flies, except for dry flies at the range 60–80 per cent.The house-fly chooses 30°C. in temperature gradients of 20–30°C. and 30–40°C. at constant humidity, expressed either in the R.H. or the S.D. scale. It chooses 30°C. with dry air if possible, but with moist air if it must. In a gradient of 33–27°C. where dry air is associated with 33°C. in the S.D. scale in the one case, and 27°C. in the R.H. in the other, it chooses 33°C. or 27°C. according as it coincides with dry air. Dry air as represented by low R.H. or high S.D. did not make any difference to its choice, consequently it is not possible to decide whether house-flies choose by the R.H. scale or the S.D. scale. The activity ofM. domesticato different combinations of temperature and humidity shows maximum activity with high temperature and low humidity, minimum with high temperature and high humidity; while in the case of low temperature combinations with either high or low humidity, activity lies intermediate in degree. High and low temperatures and high and low humidity within themselves also show significant results by the χ2test.The experimental results are explained on physiological grounds and the results obtained in these experiments are compared with those of other workers on similar problems on a variety of insects.The general experience with regard to house-flies in the field is explained in the light of these laboratory findings.For a correct analysis of the behaviour of the house-fly in nature, biological stimuli such as feeding, breeding and resting habits must be considered quantitatively in relation to environmental factors such as temperature, humidity, rainfall and light. The present work forms part of such a study.