CHAPTER XIX. 



THE RELATIONS OF ANTS TO PLANT-LICE, SCALE-INSECTS, 

 TREE-HOPPERS AND CATERPILLARS. 



" Has formicarum vaccse." Linne, " Systema Naturae," Ed. 12, I, 1766. 



" Vierment enfin ces peuplades qui couvrent la surface de la terre, et dont 

 les republiqiies sont si nombreuses que le globe ne leur suffiroit pas si la nature 

 n'eut mis de justes bornes a leur multiplication. Une foule d'insectes deviennent 

 leur proie ; la petitesse des individus est compensee chez elles par le nombre, 

 mais la force n'est pas leur principale ressource. Ce ne sont pas non plus les 

 fleurs et les fruits qui ieur fournissent leur pature ordinaire; elle est 1'objet 

 d'une Industrie plus recherchee. Les peuplades dont nous parlous, vont la 

 recueillir atipres de certains etres pacifiques qui vivent en troupes, et leur pro- 

 diguent sans contrainte les sues qu'ils savent extraire des plantes. Elles ont 

 1'art de s'en faire entendre, de les reunir dans leur habitation, et de les defendre 

 centre leurs ennemis." P. Huber, " Recherches sur les Mreurs des Fourmis 

 Indigenes," 1810. 



In gaining their wide and intimate acquaintance with the vegetable 

 world the ants have also become acquainted with a large number of 

 insects that obtain their nutriment directly from plants, either by 

 sucking up their juices or by feeding on their foliage. To the former 

 group belong the phytophthorous Homoptera, the plant-lice (Aphididse), 

 scale insects or mealy bugs (Coccidae), tree-hoppers (Membracidse), 

 lantern-flies (Fulgoridae) and jumping plant-lice ( Psyllidse ) ; to the 

 latter belong the caterpillars of the Lycasnid butterflies, the " blues," 

 or " azures " as they are popularly called. All of these creatures 

 excrete liquids which are eagerly sought by the ants and constitute the 

 whole, or at any rate, an important part of the food of certain species. 

 In return the Homoptera and caterpillars receive certain services from 

 the ants, so that the relations thus established between these widely 

 different insects may be regarded as a kind of symbiosis. These rela- 

 tions are most apparent in the case of the aphids, and as these insects 

 have been more often and more closely studied in Europe and America, 

 they may be considered first and at somewhat greater length. 



The consociation of the ants with the aphids is greatly facilitated 

 by the gregarious and rather sedentary habits of the latter, especially 

 in their younger, wingless stages, for the ants are thus enabled to 

 obtain a large amount of food without losing time and energy in rang- 

 ing far afield from their nests. Then, too, the ants may establish their 



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