186 



ANALYSIS OF THE ENVIRONMENT 



water loss. Many soft-bodied animals are 

 active at night and burrow or remain in 

 other protective niches during the day. 



6. Humidity Control 



The building of enclosed nests and 

 covered runways, as exhibited by termites 

 and ants, is a possible development from 

 burrowing behavior. This serves, among 

 other things, to help these social insects 

 gain control of the humidity to which they 

 are normally exposed. 



7. Migration, Emigration and Nomadism 

 Many birds and mammals of arid regions 



migrate when water becomes scarce or, as 

 a result of drought or for other reasons, the 

 food supply is low. Mammals in such areas 



be available comes with the power to live 

 without drinking. A common adaptation is 

 the abiUty to live on the moisture obtained 

 with food, as shown by herbivores and 

 carnivores. Even domestic cats can exist for 

 long periods with no moisture intake other 

 than that from the flesh and blood of re- 

 cently killed animals (Caldwell, 1931). 

 Many herbivores utiUze the high water con- 

 tent of plants in this manner, the insects 

 especially. Some precise data for insects 

 are given in Table 13. 



Inspection of this table indicates that a 

 number of insects, like the granary weevil, 

 contain water greatly in excess of that 

 found in their food. This seems to be the 

 usual situation even when food material is 

 relatively rich in water. Thus, the larva of 



Table 13. Water Content of Insects and Their Food (From Uvarov, 1931, after Robinson) 



are particularly given to irregular roaming 

 without definite return to a given place, a 

 type of activity aptly called nomadism. 

 Droughts may also produce the eruptive 

 types of emigration that are associated with 

 the movement of swarms of grasshoppers 

 characteristic of extensive arid lands. 



8. Water from Food and from Metabolism 



Another adjustment to Ufe in regions of 

 low humidity where liquid water may not 



the mourning cloak butterfly feeding on 

 willow leaves maintains a water content 

 slightly higher than that of the leaves on 

 which it feeds. Succulent green plants, such 

 as cabbage, may furnish a higher concen- 

 tration of water in their tissues than is 

 found in the bodies of insects feeding on 

 them. Watermelons and other plants store 

 water that is often used by animals. In ad- 

 dition, most animals make more or less use 

 of so-called water of metabolism, meaning 



