2i6 LIFE : OUTLINES OF GENERAL BIOLOGY 



For centuries there has been admiration of the parental care 

 exliibited by many insects, but who ever suspected the extra- 

 ordinary nutritive exchange or "trophallaxis" between some 

 mother-wasps or worker- wasps and the grubs in their cells? In many 

 cases the motliers or stepmothers feed the grubs with the chewed 

 flesh of insects, the jaw-apparatus of the larvae being very poorly 

 developed. Hut when the meal is supplied, and sometimes in defect 

 of it, the larva exudes from its mouth a drop of sweet elixir, which 

 is greedily licked off. In some instances the drones have learned 

 the trick, but they give nothing in exchange. This kind of intricacy 

 is being increasingly revealed. It is not that Nature is more of a 

 tangle than we thought, it is rather that the pattern of her fabric 

 is more intricate than it seemed at first. 



For a long time naturalists have been familiar with the dry-as- 

 dust meals of the wood-eating termites or white ants, and some 

 have expressed themselves puzzled by the way these insects thrive 

 on such physiologically unpromising material. But who suspected 

 that the termites can make nothing of their food unless there is 

 in their alimentary system a vigorous culture of beautiful Infu- 

 sorians, found nowhere else, which do something to the food which 

 makes it available and profitable to the termites? And strange 

 facts emerge when wc inquire how the soldiers thrive, whose jaws 

 are so big that they are not suitable for chewing wood. But we 

 have already referred to this. 



The diagram that ecology has imprinted on our intelligence is 

 that of a circle intersecting and being intersected by many other 

 circles. Thus the hollow petioles of a South American tree called 

 Tachygalia afford shelter to small beetles, which have established 

 an alimentary partnership with minute mealy-bugs. The two 

 insects live together, and the mealy-bugs, which feed on the tissue 

 inside the ix^tiole, yield a supply of honey-dew when the beetles 

 massage them, as they do somewhat forcibly. Tree, beetle, bug — 

 a triple alliance; and when certain aggressive ants appear on 

 the scene, each of these circles is intrrsoctcd. 



Ants and Aphids. — In further illustration of the intricacy of 

 inter- relations in the web of life we take a few deliberately 

 very diverse illustrations — half a dozen out of hundreds. It has 

 long been known that "honey-dew" — the sugary overflow of the 

 aphids or green-flies which feed on plant juices — is a food greatly 

 prized by many insects, and by ants in particular. Many ants 

 have learnt how to stroke the aphids so that a drop of the syrupy 

 fluid exudes. Some ants do this only when an opportunity occurs; 

 but others have come to dejx^nd on this "honey-dew" as one of 

 their principal sources of food. Such ants, as we may read for 

 example in Forel's great book {The Social World of the Ants), tend 

 the aphids as carefully as man tends his domestic animals: they 



