Marvels of the Universe 



69 



P/iolo Jy] [y. J. Ward, F.E.S. 



HOVER-FLV GRUB. 



The grub, two days old. has seized a green-fly. 

 Four limes the natural size. 



with a victim, when a three-pronged fork, or trident, 

 at its mouth is immediately thrust into the green-fly's 

 body ; so it is elevated into the air. 



The method of feeding of the full-grown grub is 

 clearlj- shown in the illustrations on page 67. The 

 grub is of a green colour, with a white stripe down the 

 centre of its back, which is tinged with purple at the 

 base. When hungry, after searching for prey, these 

 grubs are very ravenous, consuming green-flies at the 

 rate of more than one per minute. As they feed 

 during the night as well as the day, the enormous 

 amount of destruction they work amongst these garden 

 pests is incalculable ; indeed, man's insecticides and 

 fumigating devices scarcely count against the persistent 

 onslaughts of these grubs. 

 The grub's method of locomotion is curious. It is not provided with feet, but adheres to the 



leaves by means of the rough edges of the skin at the sides of its body. It consequently has some 



difficulties to overcome when on the move ; nevertheless, it travels at a remarkable pice. 



It stretches out its head — which is little more than a tapering proboscis bearing at its apex the 



trident pre\dously referred to — as far as it can reach, then, gripping the leaf by means of its trident 



and immediately drawing up its hinder parts imtil its tail-end almost touches its nose, appears as 



if about to turn a somersault. Just as you expect to see it perform that movement, however, 



its head is suddenly thrust forward again ; so it moves along in this loop-by-loop fashion. It always 



appears to be in a big hurry, both when travelling and in making its thrusts around in search of prey. 

 At the end of the ten days' feeding period, the grub's enormous appetite declines, and it attaches 



itself to a leaf or stem by the trident at its 



mouth. There it hangs for another ten or eleven 



days, its skin hardening and becoming of a 



golden brown colour. After that time has 



passed, this pupa or chrysaUs is suddenly burst 



open, and we find that the voracious grub has 



been transformed into a shining black and 



yellow-banded Hover-fly. 



It is obvious that the Hover-flies are amongst 



the gardener's most valuable allies. When we 



recognize the enormous rate of increase of which 



the green-iiies are capable, together with the 



knowledge that, if their multiplication remained 



unchecked, every green plant or tree on the sur- 

 face of the earth would soon become converted 



into living green-flies, and that, in consequence, 



the food supplies of aU terrestrial animals would 



quickly terminate, we can only marvel at the 



efficiency of Nature's sentinels-which are ever on 



guard and ready to strike. When the green-flies 



become too abundant. Hover-flies and other 



natural foes of the green-flies quickly appear, and '■'""" ''*] [•/• •'• "<"''. /■'■«•■'«■ 



the work of destruction then goes on persistently hover-,'^l'>' grub enlarged. 



,-1 ,1 1 1 1 • , 1 A portion of the previous photo enlarged to sixty 



until the normal balance is restored. ,i^„ .^^ „^,„,^i ,5,^, 



