THE EARLY STAGES OP DIPTERA. 29 



into the boxes, upon which they die in a thoroughly relaxed state, 

 ready for pinuing. From a quarter to half au hour should be 

 allowed, as if removed sooner, some may recover. Naphthaline 

 is preferable to chloroform as the latter stiffens the leg muscles, 

 making them brittle and easily broken, or causes the insects to 

 fold their legs very tightly under their bodies. 



The fumes of burning sulphur are applicable, but it is possible 

 they may act chemically on the colours in some groups. 



Rare species should always be given a small box to themselves. 



" Sweeping," t. e. dragging the net through a field of grass and 

 clover or along the sides of dry or wet ditches, is a prolific method 

 of acquiring a great number of specimens in the shortest space 

 of time possible, but a good proportion of them will be lost by 

 damage. After " sweeping " for a minute or two, the contents of 

 the net are shaken to the -bottom of it by means of two or three 

 sharp jerks, the net pinched with the left hand just above the 

 mass of seething insect life, when with the right hand a large 

 chip-box can be gradually inserted and the sides of the net strained 

 over it with the left hand, after which with very little manipula- 

 tion the lid can be replaced and the contents brought home alive.* 



Of course delicate insects will suffer by this treatment, but 

 great numbers of the hardier kinds are easily obtained thus. 

 Predaceous flies must not be kept in the same box with soft-bodied 

 ones a hungry Asilus for instance, with a Leptid or Anthomyid. 

 One soon learns with a little experience which kinds may be safely 

 mixed and which must be kept apart. 



Glass tubes are useful for capturing single specimens on walls, 

 tree-trunks, large leaves, windows and so on, but specimens should 

 never be left long in them, as moisture collects and ruins the 

 pubescence, and, in the case of small specimens, the wings also. 



A small wad of wool soaked with chloroform must be pushed 

 to the bottom of the tube and covered by a round piece of card- 

 board closely fitting the tube, with several fair-sized holes punched 

 in it. Or the bottom of the tube may be filled with plaster-of- 

 paris in which a piece of cyanide of potassium is buried. The 

 effects of this are much more permanent than chloroform, which 

 requires constant renewal. As soon as the insect is stupefied it 

 should be placed in a chip- or pill-box, where it will recover and 

 can then be brought home alive and killed by naphthaline. 



* This! s the method I have nearly always followed from my predilection 

 for bringing specimens home alive, because if killed early in the day they are 

 too stiff by the time one reaches home to be pinned successfully ; but if a 

 large-mouthed cyanide bottle does not incommode the collector in the field, 

 the end of the net may be inserted bodily into it for a few minutes, and then 

 the dead insects turned into a dry chip-box. This has the advantage of killing 

 the small spiders that generally form part of the capture and which always 

 take their toll of it. 



