of Exclusion of the House-fly. 5 



is sufficient to keep out the flies. This gentleman also confirmed my 

 previous impression, from all the inquiries I had made, that this mode 

 of excluding flies has not heen long practised in Italy and is still 

 little known there, while as far as I could learn it is entirely unknown 

 in France. 



Such being the facts connected with this subject, the next point 

 to be considered, and that which will chiefly interest the entomolo- 

 gist, is as to the causes of so unexpected a result ; in other Avords, 

 What is it that gives to these thread-nets so terrific an aspect in the 

 imagination of the house-fly, as to deter it as if spell-bound from 

 ever venturing to penetrate through their meshes, though so much 

 wider than its size demands ? and to this query I confess that I have 

 no satisfactory answer to offer. 



Tlie most plausible suj^position stated has been, that the flies take 

 the thread-nets for spiders' nets or webs, and as they are led by their 

 instinct to avoid the latter, they equally avoid the former. Several 

 objections, however, maybe urged against this exiilanatlon. In the 

 first place, judging from the numbers of flies which are constantly 

 cauglit in spiders' nets and webs, it may be doubted whether they 

 are endowed with any peculiar instinct leading them to avoid these 

 snares. In the second place, supposing the existence of such an in- 

 stinct, this feeling should lead the common house-fly chiefly to avoid 

 the horizontal webs of the house-s2)ider (ylrawea domestica, Linn.), to 

 which the thread-nets have no resemblance. And, thirdly, supposing 

 its instinct to be equally directed against the concentric-circled nets 

 of the garden-spider (^Ejjeira Diadema) to Avhich the thread-nets have 

 a greater, though still but a remote similarity, it is unaccountable how 

 the having a thorough light in the room should disjiel the ai^pvehen- 

 sion of the fly, since this very circumstance would make the thread- 

 nets more closely to resemble these spiders' concentric nets, which 

 are usually fixed in open places with a free admission of light on 

 each side. 



But in truth it is premature to speculate as to the motives of the 

 actions of the flies until the facts have been with this view more care- 

 fully obsen^ed by professed entomologists, and it is chiefly in the 

 hope that some of the members of the Entomological Society will 

 direct their attention to the subject in the course of the ensuing 

 autumn, that I have thrown together these hasty and imperfect no- 

 tices. The points to which it is most important to advert would 

 seem to be, the thickness and colour of the threads, whether those 

 of a dark are as eff'ectual as those of a light colour, and the result of 

 substituting for them thick cord or worsted ; the size of the meshes. 



