104 ANIMAL LIFE IN DESERTS 



they take refuge by day in burrows dug under 

 stones, and issue forth at night when the air is cool 

 and the humidity not very low : the ants have 

 successfully overcome the cHmatic difficulties, and a 

 number of species may be found in the Great Palae- 

 arctic Desert and in Central AustraUa ; many of 

 them come up from their subterranean nests in 

 the morning and late evening, but others are active 

 during the heat of the day. 



In the group of animals which uses burrows 

 constructed by other animals are included the 

 majority of desert snakes and Uzards (at any rate 

 in the Great Palaearctic Desert) and a number of 

 nocturnal beetles (especially some Carabidae and 

 such Tenebrionidse as Blaps). 



Many larger creatures, whose powers of movement 

 enable them to rest at some distance from their 

 feeding-grounds, take refuge in caves. Conditions 

 in a cave differ fundamentally from those prevailing 

 in the open desert : in the cave, temperature is 

 nearly constant, humidity is more constant and 

 higher than in the desert, and Hght is absent (C. B. 

 WiUiams). But for the presence of caves the 

 existence of bats in desert areas would be impos- 

 sible, but in deserts in which caves occur, particu- 

 larly if drinking-water is available, bats are fre- 

 quently numerous, both as species and as individuals. 

 Birds which nest or which roost in caves are quite 

 an important element in the fauna of the Great 

 Palaearctic Desert : examples are sub-species of 

 the Eagle Owl {Bubo bubo) and Little Owl (Athene 

 noctua), and of the Swifts (Gypselus apus, 0. murinus, 



