IN THE FIELD 223 



of temperature and moisture ? Although it must always 

 have moisture, it cannot live long in water and in very 

 wet soil ; therefore earthworms are found near the surface 

 and on higher grounds in a rainy season. In a dry season, 

 however, they retreat to lower grounds and burrow deeper 

 into the soil ; and if the drought is prolonged and the lower 

 soil too compact, they coil themselves into little balls, and 

 in this quiescent state await the showers, which enable them 

 to renew their activity. In late fall they go down below 

 the frost line, coil themselves up, and pass the winter in a 

 torpid state. In this latitude they reappear in March or 

 April, according to the weather. 



The eggs, from which complete worms hatch, are laid in 

 cocoons in the ground. 



In former lessons we learned what important factors 

 insects, birds, trees, and grasses are in the great household 

 of nature. The great English naturalist, Darwin, has shown 

 that even this humble worm performs important work in 

 the vast workshop of nature. He found that the soil thrown 

 up in their castings or pellets varied from seven to eighteen 

 tons on an acre in one year. It is plain that by the activity 

 of these worms the soil is made finer and rendered more porous, 

 therefore its fertility is increased. In some places burrowing 

 mammals transfer a very considerable amount of soil to the 

 surface. The writer has observed islands in Minnesota lakes 

 on which every foot of soil had been turned over by wood- 

 chucks, skunks, gophers, and other small mammals. Rank 

 weeds soon cover such excavated soil, showing by their 

 luxurious growth that the little folks in fur have put the 

 ground in good condition for plant growth. Have you ever 

 observed how much soil digger wasps and ants, especially 

 the latter, will bring up? From early spring until late 

 autumn you can find hundreds of small ant holes on almost 



Insect injuries on leaves, flowers, fruit, and twigs. 



