170 HONEY-DEW 



larvae to feed upon their living bodies ; and the ants watch 

 over the aphides with the greatest vigilance, driving off the 

 ichneumons whenever they approach their little prot&g&s. 



Many other insects besides ants, however, are fond of 

 the sweet secretions of the aphides, and it is probable that 

 the honey-dew thus acts to some extent as a preservative 

 of the species, by diverting possible foes from the insects 

 themselves, to the sugary liquid which they distil from 

 their food-plants. Having more than enough and to spare 

 for all their own needs, and the needs of their offspring, 

 the plant-lice can afford to employ a little of their nutri- 

 ment as a bribe to secure them from the attacks of possible 

 enemies. Such compensatory bribes are common enough 

 in the economy of nature. Thus our common English 

 vetch secretes a little honey on the stipules or wing-like 

 leaflets on the stem, and so distracts thieving ants from 

 committing their depredations upon the nectaries in the 

 flowers, which are intended for the attraction of the fertilis- 

 ing bees ; and a South American acacia, as Mr. Belt has 

 shown, bears hollow thorns and produces honey from a 

 gland in each leaflet, in order to allure myriads of small 

 ants which nest in the thorns, eat the honey, and repay the 

 plant by driving away their leaf-cutting congeners. Indeed, 

 as they sting violently, and issue forth in enormous swarms 

 whenever the plant is attacked, they are even able to frighten 

 off browsing cattle from their own peculiar acacia. 



Aphides, then, are essentially degraded insects, which 

 have become almost vegetative in their habits, and even in 

 their mode of reproduction, but which still retain a few 

 marks of their original descent from higher and more 

 locomotive ancestors. Their wings, especiaDy, are useful 

 to the perfect forms in finding one another, and to the im- 

 perfect ones in migrating from one plant to its nearest 

 neighbours, where they soon become the parents of fresh 



