Hover-Flies. 



329 



Photo by] 



[H. Bastin. 



Grouse Locust. 



Apparently a noniially formed grasshopper, it will 

 be found upon close examination that what appears 

 to be the wing-covers is really an outgrowth from 

 the fore-body forming a hard shield that extends 

 back over the wing-covers. The purpose of this 

 shield, so similar to what is found in the Mem- 

 bracids, has not been satisfactorily explained. 

 The actual length of the bodv is about half an inch. 



unbclic'\-ing gardener a demonstration of its 

 practical assistance, which may go a good way 

 towards convincing him. 



The soft, maggot-Hke grubs are broad behind 

 and taper away to a fine point forward when the 

 creature is hunting for its prey. It is pale green 

 in colour, with a white line down the middle of the 

 back. It is blind and it has no feet ; but like 

 other maggots it contrives to cling by means of 

 slight roughness of the skin, and its lower surface 

 can be so flattened out as to bring it into close 

 contact with the plant. Flattening out its hinder 

 part, it takes hold in this elementary way, and 

 extends the remainder of its body as far as 

 possible. Its mouth is provided with a triple 



spine which can be hooked into the leaf to secure its hold. Then it releases its hinder 



part and draws this forwards towards the mouth, takes hold again and extends 



the fore-part as before, proceeding much after the manner of a geometer-caterpillar. 



This ni-thod of progression, and its extremely soft and ductile body, are of great 



use to it n; the search for its victims. Having cleared the green-fly off one leaf, 



it marches up ll^e stem to the next leaf, where, taking hold with its hind-quarters, 



it elevates its bodv in the air, and sways it about from side to side. It cannot see, 



but it appears to have the sense of smell. There is a green-fly in the middle of the 



leaf, and the hover-fly grub correctly locates it. No sooner does he get within 



reach than his body is stretched 



to the full extent, and the 



green-flv is delicately impaled, 



then held triumphantly in the 



air as high as the grub can 



elevate it. It is rather like 



a drinker tilting back his head 



in order that the contents of 



a bottle may run out and down 



his throat by simple gravitation. 



Possibly the grub is helped in 



the same way, for in about a 



minute the green-fly leather- 

 bottle has been emptied of its 



fluid contents, and the useless 



envelope is dropped. The 



green-fl\' Hn'cs by suction of 



the fluids of plants, and has 



no hard parts. The grub of 



the hover-fly has only to tap 



the green-fly, and secures in 



Photo by] 



IE. Step: F-L.S. 



White-lined Hover-Fly. 



An example of these famiUar and useful flies on a scale of four times the natural 

 size. The hind-bodv is marked by connected bands of black on a yellow ground, 

 .IS in all the hover-tlies : but this species has also two light lines on the fore-body 

 behind the big compound eyes. 



