CH.X.] THE PLANT-LOUSE. 185 



In the following magnified figure (fig. 1) it will be 

 seen that the larva tapers from the head to the tail ; 



under the head is a mouth, which (fig. 2) appears 

 armed with two horny pins, and a trident-like dart ; 

 between these is the orifice of the mouth. The 

 creature has the power of emitting a glutinous se- 

 cretion, by means of which it fixes itself to a spot 

 well stocked with aphides, where, like a wolf in a 

 sheepfold, it commits the most dreadful havoc : thus 

 attached to a stem or a leaf, there is no other animal 

 of prey which hunts with so much ease. It begins 

 by turning its head in all directions, backwards, for- 

 wards, and sideways, until it meets with a plant- 

 louse, which it instantly transfixes with its dart : it 

 then contrives to adjust the body of the aphis over 

 its mouth like a cork, and in an instant the victim, 

 with its leg stretched out, is sucked dry. 



Reaumur used to make these syrphi fast a few 

 hours, and then placing one on his hand, he could 

 with the assistance of a lens see the whole operation 

 of feeding, and observe the juices, and even the 

 young aphides sucked out of the body of their parent, 

 go down the transparent gullet of the voracious 

 larva. The drained skin of the aphis is then thrown 

 aside. 



It is easy to calculate, that if they ate incessantly 

 they would destroy a prodigious number of aphides. 



Reaumur has seen a piece of stalk seven or eight 

 inches long, and covered with plant-lice, completely 

 cleared in four days by two or three aphidivorous 

 worms, 



Q2 



