72 ANIMAL LIFE IN DESERTS 



the secretions of Plant-lice during the season of 

 active growth which follows rain, and store these 

 fluids in the stomachs of certain specialized " worker " 

 ants ; these become enormously distended with 

 fluids, and are known as honey-pot ants, and from 

 them moisture is obtained during the dry period. 

 There are several genera (Camponotus, Myrmeco- 

 cystus, Melophorus) in which this habit has been 

 developed, and they are found both in the American 

 and Australian deserts. 



It is natural that, just as the insects are most 

 numerous in the clement spring and temperate 

 autumn, so they are much more numerous in a 

 season following good spring rains and a normal 

 flood than in a year in which moisture and therefore 

 annual flowers have been deficient. In this connec- 

 tion the enormous variations from the normal which 

 characterize the annual rainfall of deserts (pages 11- 

 13) will be remembered. If the regular winter rains 

 are deficient the annual plants and the butterflies, 

 bees, and other insects are scarce as regards indivi- 

 duals ; apparently also certain species are entirely 

 absent, at any rate they are so rare that they are 

 not detected. The possibility that insects and plants 

 can " carry over " an unfavourable period not of 

 months but of years requires investigation, but 

 there is a good deal of evidence to suggest that it 

 may indeed be so. For instance, Hartert was in 

 the country south of Biskra, Algerian Sahara, in 

 1908 and 1909 : he noticed white butterflies very 

 rarely between Biskra and Borj Saada, and none 

 between Borj Saada and Tuggurt. In 1912, after 



