66 



Marvels of the Universe 



THE HOVER-FLY GRUB AND ITS RAVAGES AMONGST THE 



"GREEN BLIGHT" 



BY JOHX J. WARD, F.E.S. 



To distinguish between insect friends and foes in the garden is not an easy task. The average 



gardener kills indiscriminately when insects cross his path, and especially if they happen to assume 



a grub-like form. Nevertheless, a little time devoted to dis- 

 crimination between them would be time well spent ; for his 

 wholesale killing often results in the destruction of his greatest 

 friends ; indeed, he often kills much better killers than him- 

 self. 



'Sly friend the Hover-fly has perfectly protected my sweet- 

 peas from the ravages of the " green-flies," or " blight," during 

 the extraordinary summer just passed. Although at first the 

 green-flies existed in more than usual abundance, and their 

 attacks were even more persistent than ever, 3?et the Hover-fly, 

 and his near relatives, acted so promptly, and supervised things 

 so thoroughlj-, that, later on, I could scarcely find a single 

 green-fly. 



It happened like this. By the side of my sweet-peas there is 

 a bed of mint which quickly produced its flowers. Now of all 

 things in the garden on which Hover-flies love to feast, probably 

 mint flowers stand first. So these black and pale-yellow banded 

 flies came in large numbers, and of various species, to the 

 banquet, poising themselves above the mint flowers in their 



characteristic manner, held there by the rapid vibrations of their wings, and swooping down in 



hawk-like fashion to feast as opportunity occurred. 



There was merrj^-making and love-making amongst them during every hour of sunlight ; in 



due course, too, there was marriage, and also families. It was then that my sweet-peas had 



become badly attacked with the " green blight," which, like the 

 Hover-flies, were thriving apace during the abnormal]}- hot 

 weather. It was then, too, that some of the female Hover-flies 

 became deeply interested in my sweet-peas. 



Day after day they were hovering before the flowers and 

 leaves, alighting upon them and carefully searching them over. 

 The moment they met with a green-fly, they would deposit one 

 of their eggs near to it, and then fly to another flower or leaf for 

 the same purpose. 



Now, as everyone who has tried to cultivate plants will 

 know well, green-flies possess extraordinary powers of repro- 

 duction. A single green-fly will bud out twenty or more young 

 in one day, and these are all females, which quickly develop to 

 maturit}'-, and are almost at once able to produce young in the 

 same manner as their parent, and which are again all females. 

 Photo hii} [J. J. wani. Also, this budding process of reproduction continues for twenty 



GRUB OF HOVER-FL'i'. or more generations during the summer months, without any 



The grub, photographed soon after nialcs appearing. Males are eventually forthcoming in the late 



emergence from the egg. is magnified 



about sixty times autumn broods, and after their appearance eggs are produced 



Pholo bvl [J. J. tVar.l. 



EGG OF HOVER-FLY. 



The egs here shown is magnified to 

 sixty times the natural size. 



