60 THOSE OTHER ANIMALS. 



three insect scourges ; it is enough that one aphis alone is 

 fully capable, if left to its own devices, of developing in the 

 course of a single year into a host so mighty that it would 

 cover the land and wither up and devour all green things. 

 While the caterpillar devours the substance of plants, the 

 aphis only sucks their juices, and kills by so enfeebling the 

 shoots that they are unable to put forth their leaves. It is an 

 awkward, slow-moving creature, with its heavy green body 

 swelled almost to bursting with vegetable juice, supported 

 by legs so thin and fragile that they can scarce hold up its 

 weight ; and yet it seems to pervade all nature, and to appear 

 at its season in vast armies, which fall almost simultaneously, 

 it would seem, upon the plants it affects. So sudden and 

 unaccountable is their appearance, that there are many 

 persons who have maintained, and vast numbers still firmly 

 believe, that the aphis is spontaneously produced from the 

 juices of the plants it affects. The rose-grower will go into 

 his garden and watch the young shoots from the leaves 

 making vigorous progress, and he smiles to himself at the 

 thought of how soon the sprays will be covered with rich 

 blossoms. A cold night comes, followed perhaps by a day 

 or two of dull weather. He shakes his head as he inspects 

 his bushes, and marks how the delicate young leaves are 

 slightly discoloured. He knows what will follow. Two or 

 three days later every shoot is closely packed with a layer 

 of the green fly sucking up its vital juices. It is not 

 surprising that the grower absolutely refuses to believe that 

 the whole of this infinite number of creatures were floating in 

 the air waiting to pounce upon his plants at the very instant 

 when, weakened by the frost, they are the less able to resist 

 its attacks. 



