[hewitt] FEEDING HABITS OF THE STABLE FLY 39 



The pain due to the blood-sucking operation is experienced apparently : 

 first, when the wound is made, second when the fly is increasing the 

 blood flow which it does after sucking a short time, and finally when 

 or just before the proboscis is withdrawn. Only the haustellum and 

 that portion of the rostrum below the palps take part in the rotatory 

 movements. In some cases the proboscis may be in a deflected or 

 twisted position during the whole meal ; the apodemes attached to the 

 base of the labrum are also twisted. The vibrating pharyngeal pump 

 can be readily observed. During the whole period of feeding plung- 

 ing movements of the proboscis are repeated. 



The length of time occupied in feeding varied considerably. 

 Undisturbed flies fed on the back of the hand fed from two to twenty- 

 five minutes. In the latter case the fly withdrew its proboscis from 

 the first puncture and immediately reinserted it in a new place. An 

 average length of time occupied in feeding of twenty-two meals was 

 8-9 minutes when undisturbed. 



During the feeding process, as the fly becomes gorged, con- 

 vulsive movements of the abdomen occur and clear to slightly opaque 

 drops of fluid in the case of a hungry fly, or brownish drops in the case 

 of a fly which has not completely digested its previous meal, are 

 forcibly ejected from the anus ; in the female they are ejected from the 

 upturned tip of the exserted ovipositor. In a fly which fed for 20 

 minutes, clear fluid drops were ejected from the anus at the following 

 intervals after the fly had been feeding about 11| minutes: 1 min., 

 1 min., 1 min., 1 min., 50 sees., 100 sees., 1 min., 30 sees., 35 sees., 10 

 sees., the drops were ejected to a distance of about 5 mm. and all 

 shot into the same drop of fluid. In another fly clear fluid drops were 

 ejected after feeding five minutes at the following intervals; 15, 15, 

 45, 15, 10, 20, 25 seconds. When fully gorged the fly slowly with- 

 draws the proboscis; slowly in order to take up as much as possible 

 of the extravasated blood rising up the puncture. The place of in- 

 sertion is always marked by a small drop of blood, and not infrequently 

 the fly, after withdrawing its proboscis, will lower it again and sip 

 the extravasated drop of blood; sometimes it will then plunge the 

 proboscis into the old puncture for a further drink. Occasionally 

 the fly will clean its head with its forelegs when fully gorged before 

 withdrawing the proboscis. After the proboscis is withdrawn it 

 invariably cleans its head and proboscis. The abdomen of the fully 

 gorged fly is not only more than twice its usual depth, but is also 

 about half as broad again as the normal breadth. 



