828 POPULAR SCIENCE MONTHLY. 



Thus the field ant is a great insect destroyer. A nest of this spe- 

 cies is capable of destroying as many as twenty-eight caterpillars 

 and grasshoppers a minute, or sixteen hundred an hour; and 

 such a colony is at work day and night during the pleasant sea- 

 son. In the arid plains of America the beneficent work of ants is 

 revealed in the isles of verdure around their hills. 



There are plants hospitable to ants, which furnish them shel- 

 ter and often food, within the cavities of w^hich the instincts of 

 the ants prompt them to take their abode. This is the case with 

 several ferns, among them the Polypodium nedariferum, the ster- 

 ile fronds of which bear nectaries on their lower face, and are, 

 moreover, of a shape favorable to sheltering the insect. 



Some palm trees, whose young shoots are very tender and 

 insufiiciently defended by their only half-hardened thorns, fur- 

 nish shelter to ants and receive protection from them : the Cala- 

 mus, in its spathe; some species of Dcemonorops, in a sort of 

 galleries on the surface of the stem, formed by the intercrossing 

 of the incurved thorns with which the stalk is invested. In this 

 case the sheltering organ forms only a part of the walls of the 

 cavity inhabited by the ants ; but in the large majority of cases 

 the cavity is entirely formed by the organs of the plant. 



From the examination of a large number of cases of sheltering 

 trees frequented by ants, we draw the conclusion that the bio- 

 logical relations between plants and these insects were primi- 

 tively as simple as possible, being those of plants devoured and 

 insects devouring. Such are the real relations of the harvesting 

 ants and the leaf-cutting ants with the plants which they ravage. 

 It is, however, important to observe that the plants harvested 

 from by ants do not suffer without drawing a kind of advan- 

 tage from the harvesting. Numerous seeds are sacrificed ; but a 

 large number, escaping the voracity of the ants, are scattered by 

 them and owe them for a veritable assistance in the struggle for 

 existence with rival species. 



In the complete industry of ants they do not content them- 

 selves with the simple harvesting of vegetable products, but de- 

 vote themselves to agriculture; and the plants cultivated by 

 them are, by means of the care they receive from them, favored 

 in their struggle with rival species in the same way as the cereals 

 cultivated by man, which have no longer to contend with indige- 

 nous species. Numerous ants content themselves with sweet, 

 liquid substances, as honey and nectar. Primitively, they had to 

 satisfy themselves with gathering the honey scattered over the 

 surface of the leaves; then their suction, localized at special 

 points on the leaves, may perhaps have determined the formation 

 of extrafloral nectaries. These are susceptible of rendering the 

 plants two sorts of services. Ants attracted by them to the sur- 



