72 
HOW TO COLLECT 
aqueous solution of perchloride of mercury, 1 in 500. Other 
specimens of the same species should be pinned and labelled with 
a reference to those in spirit, so that the latter may be identified. 
Killing. 
Diptera brought back alive after a day’s collecting should be killed 
by being placed for a few minutes in the closed cyanide-bottle or jar. 
If the cyanide-jar is sufficiently large, the pill-boxes themselves may 
be placed therein, first opening them a fraction of an inch on one 
side to allow the cyanide to take effect. In the case of large sluggish 
Diptera, such as Stratiomys, the pill-box may be opened without 
fear of the insect effecting its escape ; after which a smart tap on 
the bottom of the box will cause the fly to drop into the jar. 
Diptera should never be allowed to remain exposed to the effects 
of the cyanide longer than is necessary to ensure their being quite 
dead. If the poison is of reasonable strength, four or five minutes 
should be sufficient to kill even the largest and strongest Hies; on 
the other hand, it is necessary to make sure that the insects are 
really dead, since, if the exposure to cyanide has been too short, flies 
will often appear to be dead when in reality they are only stupefied. 
As soon as the insects are really dead, they should be removed from 
the killing-jar; those in pill-boxes maybe allowed to remain therein 
until one is ready to pin them, while the loose specimens should be 
turned out on to a sheet of cork-carpet or pith. 
Methods of preserving Diptera other than by pinning. 
Diptera should always be pinned, and this should be done as soon 
as they are dead. If preserved in any other way, they will never 
make such satisfactory specimens. 
When, however, it is impossible to pin them, Dipitera may be 
preserved in fine sawdust, on which a few drops of dilute carbolic 
acid should be sprinkled to prevent mould. Each specimen, before 
being placed in the sawdust, should be loosely screwed up in fine 
tissue-paper (cigarette-paper would do), on which the necessary data 
(see below under “ Pinning ”) should be written in pencil. To contain 
the specimens a small tin box (such as those in which tobacco is sold) 
should be used ; and to prevent injury from shaking, the box should 
be packed quite f ull of sawdust and specimens, 
