THE FOOD OF THE OTHER LAND ANIMALS 97 



The true worms, or annelids, are represented on land by the 

 earth-worms, the land leeches, and the onychophores. Earth- 

 worms are found all over the world, living in burrows in the 

 ground or in decaying material. They swallow earth and pass 

 it through their bodies, digesting out of it some of the organic 

 matter it contains, a manner of feeding adopted by very few 

 insects, though duplicated in the snails. Darwin calculated 

 that there were on an average 53,000 earth-worms in an acre 

 of garden ground, and that they passed 10 tons of soil annu- 

 ally through their bodies. Some earth-worms grow to a very 

 large size, five or six feet in length, but most of them are a 

 few inches long. They furnish food for the young of certain 

 parasitic flies and certain fire-fiies and probably also of other 

 predaceous tjT^es, for some centipedes, some snails, and the land 

 planarians, for moles and occasionally other mammals, and for 

 various birds, and they are always much infested with internal 

 parasites. The land leeches in the eastern tropics are few in num- 

 ber of kinds, but abundant in individuals in suitable locations, 

 and greedily suck blood. The onychophores are curious worm- 

 like creatures, active at night, which feed on various insects which 

 they catch by spitting liquid silk at them by which they are 

 hopelessly entangled; they live in the tropics and in the south- 

 ern hemisphere, and for the most part are rare and local. 



Closely allied to the insects are the crustaceans, including 

 the lobsters, crabs and similar creatures. The common wood- 

 lice, pill-bugs or sow-bugs, found in rotting wood, under logs, 

 etc., sometimes in ants' nests and in cellars, occur everywhere. 

 They live chiefly on damp decaying vegetable matter. The 

 land crabs of the tropics and some crayfish are almost entirely 

 terrestrial, though not well adapted for terrestrial life. They 

 feed on plants and dead vegetable matter, and sometimes on 

 carrion; one of the best known of these is the famous eastern 

 robber crab which climbs cocoanut trees. As compared with 

 insects the land crabs and crayfish are very large and pow- 

 erful; but the number of kinds is limited, and most of them 

 do not go very far from water. 



