155 



"' has, of course, a positive value only ; and no doubt in many places 

 the flies were overlooked, either because they were present in small 

 numbers, or because the conditions were unfavourable the day may 

 have been wet or cloudy, or the locality may have been visited in 

 the early morning before the flies were abroad." " My own rule," 

 adds this author, " and the instructions I gave to my collectors, was 

 to stop at every stream or closely wooded spot for half an hour. 

 If in this time no tsetse-flies were seen, it was concluded either 

 that they were not present, or that they were present in such small 

 numbers that, for all practical purposes, they were not a menace to 

 cattle or transport animals." 



KILLING TSETSE-FLIES AFTER BEING CAUGHT. Tsetse-flies " 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 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 

 flies ; 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 may be 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." 



PINNING TSETSE-FLIES ; THEIR TRANSMISSION TO ENGLAND. 

 Except when intended for dissection, Tsetse-flies should invariably be 

 pinned, and this should be done as soon as they are dead. The 

 operation of pinning is quite simple, and does not take long, but 

 attention should be paid to the following points : 



The specimen must never be allowed to remain close to the tip of 

 the pin, but should be drawn two-thirds of the way up the latter, which 

 should then be handled by grasping it with the entomological forceps 

 below the fly. 



Wings and legs must be arranged, so far as possible, by means of 

 the mounted needles or fine-pointed forceps ; wings must not be left 

 closed over the body in such a way as to conceal the upper surface 

 of the abdomen, nor must the legs be permitted to remain tightly 

 flexed beneath it. 



Specimens must be pinned through the thorax. 



If but a single example of a species has been obtained, it should be 

 pinned on its side. 



If two specimens of a species have been caught, pin one on its side 

 and the other in the ordinary way, in the latter case thrusting the pin 

 vertically downwards through the centre of the thorax. 



For purposes of identification, whenever possible at least six 

 specimens, including examples of both sexes, of a species should be 

 obtained. 



