606 INSECTS AT II03IE. 



the back, and through the aperture the head and legs of the 

 Gnat show themselves. In a short time the Grnat draws itself 

 entirely out of the pupal shell, and uses it as a kind of raft on 

 which it can stand while it shakes out its damp and crumpled 

 wings. So small a creature does not require any long time for 

 this process, and as soon as it is completed the Gnat flies 

 merrily away. 



I have been often asked to give some hints as to the extir- 

 pation of these insects. There are but very few that can be given. 

 In all places where ponds and stagnant waters are near, nothing 

 can be done. But I find that the chief nursery of the Gnat is 

 tlie open rain-water-butt. 



The ordinary cover is useless as a protection from Gnats, as 

 the delicate little flies can insinuate themselves through very 

 small crevices. With regard to my own butt, I first nail down 

 the ordinary wooden cover, and then run a broad strip of 

 canvas round the upper part of the butt, fastening the lower 

 edge to the butt, and nailing the upper edge on the wooden 

 cover. I also caulk with tow any crack in the cover, and with 

 the same substance fill in the space between the rain-water 

 pipe and the sides of the hole in the cover through which it 

 passes. There has been a notable diminution of Gnats since 

 these precautions were taken, and I am sure that if every 

 water-butt were similarly protected, the number of Gnats that 

 get into houses would be diminished at least ninety per cent. 



Eeference has been made to the too familiar hum of the 

 Gnat. This sharp and almost trumpet-like sound has been 

 carefully investigated, and by means of an instrument known as 

 the Siren it is possible to count the number of beats made in a 

 given time by the wings of the Gnat. The Siren is an 

 instrument which can produce any required number of vibra- 

 tions, and as-they are produced registers them on a dial. Now 

 it is found that when the vibrations exceed a certain number 

 per second, a definite musical sound is produced, the sound or 

 tone becoming sharper in exact proportion as the number of 

 vibrations becomes greater. So, if a Gnat be heard to hum, 

 and a Siren be forced to produce the same note, the instrument 

 not only gives the exact note, but registers on its dial the 

 number of vibrations required to produce that note — in other 

 words, the number of vibrations of the Gnat's wing per second 



