J. E. Rombouts

“ It is proper to add, however, that a fly running on a window has only three or four of its feet on the glass at a time, and that therefore only half of its hairs, or 5,000 or 6,000 of them, are serving it at once. I repeated my experiments, to determine the weight hairs are capable of supporting when suspended in the manner I have described, and found again that a hair 0·06 of a millimetre in diameter will bear a weight of 0*00045 of a gramme ”

“ The absurdity of this supposition is readily apparent on examining glass with the microscope; and no naturalist can be found in these days to uphold it. Another theory, which has been frequently advanced, explains the fact by affirming that the feet terminate in little suckers, by the application of which to the smooth surface the insect is able to adhere by the force of the pressure of the air, in the same manner that the street-boy fastens his leather sucker tightly to the flagging. ”

“ After it has rubbed its feet against one another for a short time, and has passed its wings over them, the dust will be found to have disappeared, and it will again be able to walk on glass. The object of this labor, which flies may be observed to be performing at every moment, is not, then, as was once supposed, to cleanse the wings, but to keep the feet in good condition to stick on smooth surfaces. ”

“ And a fly which has been put upon a glass so covered, and is then transferred to a clean glass, will not be able to adhere to that till after some interval. An extremely thin coating of oil is enough to bring about a failure to adhere; even the rubbing of the finger on the glass is sufficient. ”

“ IT was believed at one time that flies and some other insects owe the faculty of running over smooth bodies like glass to the numerous hairs with which their feet are provided catching in the pores of the material. ”

“ A hair more considerably magnified.
of 0·12 of a millimetre will bear 0·00085 of a gramme; consequently, a diameter of a millimetre will bear 0·007 of a gramme, and the six feet together 0·042 of a gramme.
It is very difficult, if not impossible, for a fly to walk on a vertical polished surface when it is thinly covered with dust. When, after it has made the effort, we examine its feet with the microscope, we shall perceive that the interspaces between the hairs are filled with dust. ”

“ The insect, struggling for liberty, places his pulvilli against the glass, and leaves after each effort, traces that may be observed very distinctly, for they are perfectly visible in a good light (Fig. 2) .
We may discover, whenever the feet of the fly come again into contact with these tracks or minute drops, that they are composed of a very liquid substance, for they spread quite readily on the glass. We can not admit, as some naturalists assume, that the liquid can hold the club-shaped hair-ends by suction. If this were the case, the ends ”