286 ] The Wonderful Ways of Insects and Spiders 



regions centipedes are small and generally use their poison for 

 killing insect prey. In tropical regions there are larger species of 

 centipedes; their bite may have serious consequences for human 

 victims. 



The Lowly Worms 



Many a child who digs earthworms for fishing bait thinks he 

 is collecting "insects." This idea is indeed very far from the truth. 

 Worms are not closely related to any other creature; in the animal 

 kingdom they occupy their own major niche, just as distinct as 

 the division of "vertebrates" to which man belongs. 



Scientists have classified the many kinds of worms in three 

 main groups, and each of these forms one of the eleven major 

 divisions of the animal kingdom. Some of our most troublesome 

 parasites, such as tapeworms and hookworms, belong to two of 

 these divisions "roundworms" and "flatworms." 



How EARTHWORMS ENRICH THE SOIL 



In the third group ("segmented worms") we find our friend 

 the earthworm. "Friend" it is indeed, for earthworms are of im- 

 mense value to man in growing food. As they move through the 

 ground they do not push the earth around their bodies as a mole 

 does; they actually swallow it! Before they expel the earth again, 

 it is ground fine in the gizzard and lime is added to it in the 

 stomach. 



Earthworms usually plow a foot or more beneath the surface 

 of the earth, and are constantly bringing subsoil upward. They 

 also carry down with them from the surface bits of dead leaves, 

 flowers, and twigs, which enrich the soil as they decay. Charles 

 Darwin estimated that an acre of garden land in England held 

 more than fifty thousand earthworms, and that eighteen tons of 

 vegetable mold passed through each earthworm's body every year! 



Tug-of-War: If a child watches a bird tugging at an earthworm, 

 he may wonder what enables the worm to "hold on." The holding 

 is done with strong muscles aided by tiny stiff bristles that cling 

 to the earth. There are four pairs of bristles on each segment 



