124 ANIMAL LIFE IN DESERTS 



of dormancy, some of them as pupse, others as eggs, 

 others probably as resting larvae. A few species 

 prolong their season of activity and produce a 

 series of broods by utiUzing first one food plant and 

 then another, as the plants successively become 

 available. A good example is furnished by Papilio 

 machaon, the Swallow Tail Butterfly, in Mesopo- 

 tamia. In April and May it fed on the flowers of 

 Ruta tuherculata, and as this plant began to go to seed 

 Ammi ma jus came into flower, and became for the 

 moment the plant on which eggs were most com- 

 monly laid. This plant was followed by Ducrosia 

 anethifoUa, which was not common, and probably 

 not an important food plant. While A, ma jus and 

 D, anethifolia were running to seed, Ammi visnaga 

 flowered and became an important food plant ; it 

 was in full flower in June after the first three were 

 quite dry. A fifth plant, Foeniculum vulgare, was 

 also found to be eaten by the larvae of P. mxichaon. 

 It seems then in Mesopotamia that the Swallow 

 Tail Butterfly has a regular succession of food 

 plants belonging to two unrelated natural orders 

 of plants — the Ruta to the Rue family, the others 

 to the Umbelliferae (Peile). One might argue from 

 this that if a caterpillar or other plant-eater pos- 

 sesses the power of living on a variety of plants it 

 may be able to survive under conditions which 

 would exterminate another caterpillar that could 

 only feed on one plant : in fact, that polyphagy 

 may be one factor determining the survival of 

 certain species in the desert. 



In rather a similar way I noticed in Mesopotamia 



