48 GENERAL BIOLOGY 



Individually aphids are insignificant, but collectively 

 their drain upon the plant mav be very serious. Each 

 aphis is an animated sap pump. It sits quietly on bark or 

 leaf, with its proboscis immersed in the green tissues, and 

 pumps by the hour, scarcely changing its place or moving 

 by more than an occasional sweep of its long antennae. 

 Its food consisting of sap, contains considerable sugar 

 much more indeed than the creature is able to assimilate. 

 This excess of sugar is discharged from time to time, along 

 with the other rejectamenta and excreta of the body, in 

 fluid drops of "honey dew." 



Honey dew is very sweet and palatable. It is gathered 

 from the leaves where it falls by ants, bees, wasps and other 

 animals. Bees store it as honey, and although it is not the 

 best of honey still it is not unwholesome, and men eat it 

 gladly. When aphids are abundant on growing trees 

 honey dew is often secreted in large quantities. A sudden 

 jarring of an aphid covered bough may cause such a sudden 

 and simultaneous discharge by the aphids that the honey 

 dew will fall in a shower of fine spray. It often covers the 

 lower boughs of trees and the bushes beneath them, with a 

 shiny, sticky, sweet coating. 



That ants have a "sweet tooth" everyone knows from 

 observations in his own pantry or lunch basket. They like 

 honey dew, and from gathering it at large, they have passed 

 to gathering it at its source from the aphids themselves. 

 The relations between the two that find their simplest ex- 

 pression in chance visits by ants to aphid colonies, become 

 much more intimate when ants begin to guard and care for 

 the aphid flocks, to build shelters for them, or to share their 

 own homes and fortunes with them. 



These relations may be grouped in three categories : 



i. The chance feeding by ants on the honey dew offered 

 by aphids. This is hardly more than accidental associa- 



