ANIMALS THAT LIVE WITHOUT WATER 15I 



teus (which is too bitter for man), while the juice of 

 the barrel cactus (Echinocactus) may furnish several 

 pints of fluid which even man can drink. Many if not 

 most of the succulent plants are thorny, and though it 

 may be thought that this thominess is a protective adap- 

 tation against thirsty animals, it is more likely that it 

 is merely an outgrowth of the homy, hypertrophic cuti- 

 cle and that any protective value is incidental. 



As the annual and tuberous-rooted plants show marked 

 seasonal activity, so also do a great variety of animals. 

 Between the rains, the grasshoppers, beetles, and other 

 insects disappear into the earth, and in many species the 

 reproductive cycle places them in an inactive larval or 

 pupal stage below the ground in the dry season, to ap- 

 pear again, sometimes in abundance, with the short- 

 Hved annual vegetation. Some are abundant in mid- 

 summer, not because midsummer conditions suit them 

 particularly but because several months before there had 

 been food and water for the larvae. Ants, which are gen- 

 erally insect eaters, tend to follow the rest of the insect 

 cycle, but many live on plant juices or the secretions 

 of plant Hce which are accimiulated dviring a period of 

 abundance. Specialized workers store these foods in the 

 stomach, and become so distended that they are known 

 as honey-pot ants. 



Lizards and other desert reptiles can probably subsist 

 on the preformed and metabohc water of the insects 

 which constitute their food, but no reptile, so far as is 

 known, can live on dry food such as seeds. The Amphibia 

 are at an even greater disadvantage: frogs and toads 

 must burrow into the earth where there is substantial 

 humidity, emerging only at night, and during the dry 

 season they pass into a state of relative inactivity below 

 the ground, sleeping in the subsoil moisture. 



The migratory birds, living on ants, insects, frogs, or 

 lizards, may invade the desert in increasing nimibers dur- 

 ing the lush season, but relatively few have estabhshed 



