DIRECT INJURIES CAUSED BY INSECTS. 



103 



Our friend Captain Green, of the sixth regiment of the East 

 India Company's native troops, relates to me, that in India, 

 when the mangoes are ripe, which is the hottest part of the 

 summer, a very minute black fly makes its appearance, which, 

 because it flies in swarms into the eyes, is very troublesome. 



tormenting in Sweden (see Amcen. Acad. iii. 343.), and also in the United 

 States, Avhere Mr. Stewart and Capt. Marryat make frequent and grievous com- 

 plaints of them, the latter asserting that in some places they were fifty to the 

 square inch, as I believe they literally were in a small inn where we took break- 

 fast in September 1830, on our road to Chamouni from Geneva. 



It is a remarkable, and, as yet, unexplained fact, that if nets of thread or string 

 with meshes a full inch square, be stretched over the open windows of a room in 

 summer or autumn, when flies are the greatest nuisance, not a single one will 

 venture to enter from without, so that 4iy this simple plan a house may be kept 

 free from these pests, while the adjoining ones which have not had nets applied 

 to their windows, will swarm with them. In order, however, that the protection 

 should be efficient, it is necessary that the rooms to which it is applied should 

 have the light enter by one side only ; for in those which have a thorough-light 

 the flies pass through the meshes without scruple. For a fuller account of these 

 singular facts, the reader is referi'ed to a paper by W. Spence in Trans. Ent. Soc. 

 Lond. vol. i. p. 1., and also to one in the same work, vol. ii. p. 45. by the Rev. 

 E. Stanley, now Lord Bishop of Norwich, who having made some of the expe- 

 riments suggested by Mr. Spence, found that by extending over the outside of 

 his Avindows nets of a very fine pack-thread with meshes \\ inch to the square, 

 so fine and comparatively invisible that there was no apparent diminution either 

 of light or the distant view, he was enabled for the remainder of the summer 

 and autumn to enjoy the fresh air with open windows without the annoyance he 

 had previously experienced from the intrusion of flies, often so troublesome that 

 he was obliged on the hottest days to forego the luxury of admitting the air by 

 even partially raising the sashes. " But no sooner (he observes) had I set my nets 

 than I was relieved from ray disagreeable visitors. I could perceive and hear 

 them hovering on the other side of my barriers ; but though they now and then 

 settled on the meshes, I do not recollect a single instance of one venturing to 

 cross the boundai-y." 



It is singular, too, as was first pointed out by Mr. W. B. Spence ( Ent. Trans. 

 i. 7.) that Herodotus 2200 years ago stated that the Egyptian fishermen pro- 

 tected themselves in a similar manner from the attacks of mosquitos by spreading 

 their fishing nets over their beds, a fact wliich has greatly puzzled all his com- 

 mentators, who, not conceiving the possibility of mosquitos being kept oflT by 

 fishing-nets which must necessarily have wide meshes, have supposed the father 

 of history to have alluded to some protection of fine linen similar to the gauze 

 nets now used against these insects. But in this, as in so many other instances, 

 the supposed error is not that of Herodotus, but of his commentators, who, igno- 

 rant of the fact above related as to flies being excluded by wide-meshed nets, 

 could not conceive of it in the case of mosquitos ; yet, in confirmation of its accu- 

 racy, I have been told by a friend that he was assured by a gentleman, who had 

 travelled in America, that he had often had mosquito nets with meshes an inch 

 square put over his bed, and had found them a perfect security from their bites, 

 though, as is well known, they will creep through any small hole in an ordinary 

 gauze net. 



In concluding this long note it may be observed that the nvmiber of house 

 flies might be greatly lessened in large towns, if the stable dung in which their 

 larva? are chiefly supposed to feed, were kept in pits closed by trap doors, so that 

 the females could not deposit their eggs in it. At Venice where no horses are 

 kept, it is said there are no house flies, a statement which 1 regret not having 

 heard before being there, that I might have inquired as to its truth. 



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