INTERDEPENDENCE OF ORGANISMS 



49 



Fro. 37. — Aphid colony on a leaf of Ceanothus, 

 attended by ants seeking honey dew. h, a 

 larva of a syrphus fly, feeding on a wingless 

 aphid. 1', a winged aphid. /, an ant patting 

 an aphid with its antennae, k, the empty 

 skin of an aphid that has been parasitized. 



tion. It may be recognized in an aphid colony that 

 is attended by one kind of an ant on one day, by another 



kind on another 

 day, and is part of 

 the time unattend- 

 ed. 



2. The habitual 

 guarding of aphid 

 colonies by ants, 

 safeguarding their 

 own supply of 

 honey dew. — This 

 is the commonest 

 type of association, 

 and the one easiest 

 to observe. I n 

 summer or autumn, on many a curled dock orthistle or dog- 

 wood bush, wherever ants are seen gathered together upon 

 the green foliage, there one may expect to find on 

 closer inspection, an abundance of aphids as well. 

 And if one approach quietly and watch carefully 

 he may see the ants moving about among the 

 aphid herd, fondling them with their antennae, patting 

 or stroking an individual here and there, and obtaining 

 sometimes as a response, the extrusion of a drop of honey 

 dew, which is lapped up as soon as it appears. The ants 

 will often be seen to drive away intruders — chiefly winged 

 parasitic insects, which seek to lay their eggs upon the 

 bodies of the aphids. They will even rush at an intruding 

 finger, and attack it fiercely, though ineffectively, with their 

 jaws. Yet, though they show great dash and courage in 

 dealing with any parasitic syrphus fly or ichneumon that 

 ventures too near the flock, they show a sad lack of insight 

 in allowing the egg, when one has been successfully laid by 



