4．Earthworms that Help Improve the Soil
The earthworm is a useful animal．Out of the ground，it is food for other animals．In the ground，it makes rich soil for fields and gardens．
Earthworms dig tunnels that loosen the soil and make it easy for air and water to reach the roots of plants．These tunnels help keep the soil well drained．
Earthworms drag dead leaves，grass，and flowers into their burrows．When this plant material decays，it makes the soil more fertile．
No other animal is so useful in building up good topsoil．It is estimated that in one year fifty thousand earthworms carry about eighteen tons of fine soil to the surface of an acre of land．One worm may add three quarters of a pound of earth to tho topsoil．
4．帮助改良土壤的蚯蚓
蚯蚓是一种有益的动物。来到地面上，它成了其他动物的食品，而在地里，它却为田地和花园制造着肥沃的土壤。
蚯蚓挖掘风洞，使土壤变松，并使空气和水容易抵达植物的根部。这些风洞有助于土壤迅速排水。
蚯蚓把枯树叶、草和花朵拖进自己的洞中，这种植物性物质腐烂后，便使土壤变得更肥沃了。
在制造优良的表面土壤方面，没有别的动物能像蚯蚓这样有用。据估计，一年中，5万条蚯蚓能把大约18吨的细壤送到1英亩土地的表面，一条蚯蚓也许能把3／4磅的土壤加到地表层。