Observations on a mode practised in Italy of excluding the common house-fly from apartments / by William Spence.

  • Spence, William, 1783-1860
Date:
[1836]
Catalogue details

Licence: Public Domain Mark

Credit: Observations on a mode practised in Italy of excluding the common house-fly from apartments / by William Spence. Source: Wellcome Collection.

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    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 been 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 words. 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. The most plausible supposition 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, may be urged against this explanation. In the first place, judging from the numbers of flies which are constantly caught 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-spider (Aranea 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 (Epeira Diademo) to which 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 dispel the apprehen¬ 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 observed 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 effectual as those of a light colour, and the result of substituting for them thick cord or worsted; the size of the meshes.