Further reports (no. 4) on flies as carriers of infection.

Date:
1911
Catalogue details

Licence: In copyright

Credit: Further reports (no. 4) on flies as carriers of infection. Source: Wellcome Collection.

    7/52 (page 5)
    and the general topography of the immediate neighbourhood; the village of Postwick lies roughly E. of the tip, and the prevailing wind is S.W. It was difficult, if not impossible, definitely to prove that flies were not attracted from the leeward side of the refuse by the smell of the decaying matter, and it would be surprising if a certain number were not so attracted. Experiments carried out by one of us (F.M.H.) on the biting Muscid Stomoxys calcitrans and an Acalyptrate Muscid (Dacus) have shown that flies may be attracted by certain smells in a very definite way from considerable distances, but that the reaction to such smells is—to some extent at least—a sexual characteristic, the females responding more readily to the smells which advertise a place suitable for egg-laying. Hence any^ accumulation of refuse such as we had here to deal with, might, by analogy, be expected, if exerting any marked effect in this direction, to attract from the surrounding country a larger number of females than of males. Four lots of flies were caught at intervals of a month, in July, August, September and October. The sexes of the first lot were not noted, they being those sent to Mr. E. E. Austen for identification. The remaining three lots were examined and identified by one of us, and these were all caught under similar conditions, in balloon-traps placed in the workmen’s hut. The results were as follows :— Males. Females. August ... 329 334 September 302 318 October ... 158 243 It is known that under normal conditions the sexes in the case of M. domestica are produced in approximately equal numbers. The greater proportion of females in the last as compared with the very equal numbers of the two previous catches, is probably due to the fact that, in autumn, males tend to die off, and are not replenished by fresh broods, while the females live on and hibernate. The great preponderance of Musca domestica is noteworthy. More than 99 per cent, of the flies caught in the village on fly- papers and tapes were M. domestica, the remainder mostly Homa- lomyia canicularis. As shown by the map, there is on the west of the tip a sewage farm. If house-flies were attracted from the district by the smell of the tip it is not unreasonable to suppose, though it by no means follows, that a certain number might be attracted by the smell of the sewage effluent, which at times was almost equally penetrating though of a slightly different character. This, however, was not the case, for although great numbers of Scatophaga and Sepsis were seen about the effluent channels, M. domestica was practically absent. The way in which house-flies congregated in the warm and rather ill-lit shelter-hut was very noticeable. On cold days it was often not easy to catch any flies on the tip itself, but they could be caught in any number in the shelter, where some sacking, which covered the wall and a bench near the stove, was sometimes literally “ black with them.” Though the flies caught in the workmen’s shelter, like those caught in houses in the village, were practically all M. domestica,