ANIMAL AGENCY IN SOIL -MAKING. 487 



The effect of this action of ants on the soil-material is peculiar. 

 The tendency is like that noted by Mr. Darwin in the case of earth- 

 worms to bring the finer particles to the surface. I am inclined to 

 think the ants accomplished this part of their work even more effect- 

 ively than the earth-worms, for the reason that they penetrate more 

 deeply between the stones than their less active associates. Like the 

 earth-worms, but in larger measure, the ants convey considerable 

 amounts of organic matter into the soil.- Their winter store of food 

 is deeply buried, and much of it remains unconsumed in the nether 

 earth. There is thus a constant inhumation of vegetable matter be- 

 neath the materials which they bring to the surface. 



Although the burrowing vertebrates operate most vigorously in the 

 forest-covered regions, they also exercise a certain influence on the 

 open country. The moles which work only here and there in the for- 

 est are conspicuous agents in overturning the soil in the grassed regions. 

 Still, as this group is peculiarly limited in its distribution, and rarely 

 penetrates to more than four or five inches below the surface, it exer- 

 cises a relatively small effect. The field-mice are more potent agents 

 in effecting the character of the soil. Their dwelling-chambers are at 

 a considerable depth below the surface, and in forming them, they 

 bring a certain amount of matter to the open air, moreover the re- 

 mains of their food, as well as their excrements, are important contri- 

 butions to the organic matter of the soil. Insects in their laiwal stage 

 exercise a less effect in the open field than in the forest-covered regioi^ ; 

 still, they are not to be left out of account in considering the process 

 of soil-making in such areas. In Europe the rabbit, which has a habit 

 of burrowing to a considerable depth, and in certain districts west of 

 the Mississippi, the prairie-dog, overturn the soil on the areas they 

 occupy with considerable rapidity. Still, as the number of these creat- 

 ures in any given district is not great, their influence is mostly exer- 

 cised in a very local way. 



The foregoing considerations make it tolerably clear that our ants 

 are, in some districts, by far the most important agents in overturning 

 the soil and in commingling the superficial organic matter with the 

 mineral material of which it is composed. Although on a field of a 

 certain class those which are of a clayey nature, the earth-worms, are 

 probably more efficient soil-makers than the ants, this latter group ap- 

 pears to be, at least in the eastern part of North America, on the 

 whole, by far the most effective in the preparation of the soil for the 

 needs of plants. They do not, it is true, take the soil into their bodies 

 and thus disintegrate it, as the earth-worms do, but they accomplish 

 what is perhaps the more important task of rapidly overturning the 

 soil-material as well within the forests as in the open fields wherever 

 that material is of a sandy nature. 



