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THE HABITS OF A DIPTERON PREDACEOUS ON MOSQUITOS 



IN NYASALAND. 



By W. A. Lamboen, M.R.C.S., L.R.C.P. 



On 12ih. September 1919, while watching at a pool near Kotakota, Lake Nyasa, 

 the emergence of mosquitos from their pupae, which in the case of this particular 

 species takes place mostly between 4.30 p.m. and dusk (about 6.30 at that time 

 of year), the writer saw at rest on some scum on the surface of the water, an An- 

 thomyiid fly of the genus Lispa, which after a few minutes made a sudden rush 

 at a mosquito just emerging from its pupa-case. The mosquito with its wings 

 still unexpanded and part of its legs and the hinder segments of its abdomen stiU 

 within the pupa-case was absolutely at its mercy. The fly grappling it from behind 

 with its front legs proceeded to thrust its proboscis into the thorax. The fly was 

 by no means timid, and it was possible to lean over and approach one's head to watch 

 the proceedings so closely that it was even possible to determine by its antennae 

 the sex of the unlucky mosquito ; it was a male. The fly was captured before 

 it had finished its meal, lest it should suddenly fly up and escape. 



Next morning the pool was again visited and quite a number of the same flies 

 were observed on the scum. One was seen to make a sudden thrust with its pro- 

 boscis into the water, at the edge of the scum, followed by a series of similar but 

 smaller eflorts, as if it had seized some body, though insecurely at first. Presently 

 it raised itself and partly drew out of the water a mosquito larva, about half-grown, 

 impaled on its proboscis, which it proceeded to suck. The larva was not seen to 

 move, possibly being paralysed by some buccal secretion from the fly. Advantage 

 was taken of the fly's lack of timidity to push beneath the scum a broad stick 

 on which it and its victim were gradually raised, so that the feeding process could 

 be studied as near at hand as one wished. A good series of the flies, subsequently 

 taken, were all removed in this manner, the stick being thrust into the mouth of a net 

 which was then closed. 



One fly was seen on the same occasion to grasp and thrust its proboscis into a 

 mosquito, a female, which had failed to emerge completely from its pupa and may 

 or may not have been dead at the time ; it was not seen to move at all. The 

 rest of the series were all seen at one time or another attacking mosquito larvae, 

 not always with success, but when successful dragging them out of the water and 

 sucking their juices. 



On 13th September, the emergence of a Ciilex was witnessed almost from the 

 first ; the thorax bursting its covering, the imago then extracting its head, the rest 

 of the body following until the wings and some of the legs were free. At this point 

 a LisjM, which had been resting about four inches off on some scum, approached 

 deliberately on the surface film, grasped the still soft Culex with its forelegs, and 

 thrust its proboscis into the thorax, dragging the mosquito beneath its body to a 

 little piece of leaf, about two inches off, floating on the water. As the captor 

 walked, one could see quite clearly the legs of the victim trailing beneath. The 

 fly with its prey was then taken. The mosquito, a female, was still alive and 

 moved its legs feebly. 



