102 S. HADWEN AND A. E. CAMERON. 



1917, there is little doubt but that the last-named species will be found to occur 

 in British Columbia, as it has been reported in neighbouring regions of the United 

 States from Western Montana. 



Professor W. Lochhead (11) quotes the opinions of two correspondents from 

 Western Canada, one from Saskatchewan. It is the idea of the first that the " nose- 

 flies " arrived in the western territory eight years ago and were first observed about 

 a year after the importation of some horses from the United States, from which the 

 parasites may have been obtained. The second states that the " nose-fly " 

 (apparently referring to 67. haemorrhoidalis) made its first appearance in Saskatchewan 

 some ten or more years ago and supposes it to have been brought from the United 

 States or Mexico. 



Period of Adult Activity. 



In the vicinity of Saskatoon, 67. nasalis is on the wing from the middle of July 

 until the middle of August, although a specimen taken by Mr. T. N. Willing, of 

 Saskatoon, at Maple Creek, Sask. , is dated 30th October 1903. Eggs of this species 

 that were collected in the first days of August were found to have already hatched. 

 Our first specimen of 67. haemorrhoidalis was taken on 11th July 1917, and the last 

 on 11th August. It is probable that the adult activities of these two suedes are 

 seasonally contemporaneous. 67. intestinalis makes its appearance somewhat later 

 than the other two, the first capture having been made on 22nd July 1917, and the last 

 on 22nd August. On the Pacific Coast, 67. intestinalis is found on the wing much later 

 in the season. On Vancouver Island, a specimen was taken on 5th October 1917, 

 whilst on 3rd October several were observed in copula, the flies being then very 

 numerous. 



Habits of Adults. 



The three species of Gastrophilus are most active on bright sunny days, attacking 

 their hosts when the weather is warm. Wind has apparently but a slight restraining 

 influence. All three are strong on the wing, although 67. intestinalis is least rapid in 

 its movements. As regards their effect on horses, it has been observed that the attacks 

 of 67. nasalis and 67. haemorrhoidalis inspire the animals with more acute nervous- 

 apprehension than do those of 67. intestinalis. Persistent attacks will drive horses 

 that are grazing in the open almost frantic, and a mad stampede on a warm day is 

 a fairly sure indication that bot-flies are in the immediate vicinity of the animals. 



In an endeavour to prevent the attack of 67. nasalis horses are often observed 

 standing head to head, resting their jaws on each other's necks. By adopting this 

 attitude the host can the better protect itself against the fly as it " strikes " upwards 

 to oviposit between the rami of the mandibles. When in harness, the animals strive 

 to ward off the fly by drawing the head back quickly towards the neck, but the action 

 is apparently not rapid enough to prevent the insect accomplishing its purpose. 

 An egg is generally left behind, securely fastened to a hair at each attack. 



In darting at the lips, 67. haemorrhoidalis will cause the animals to nod their heads 

 violently, to strain them forward and to open their lips. On repeated annoyance 

 they endeavour to rid themselves of the irritating pests by rubbing their lips 

 vigorously on the ground or any convenient object. With this species, as with the 

 last-mentioned, the adult makes its attacks insidiously from below and is often 



