38 NATURAL HISTORY OF GLOSSINA PALPALIS 



to be reattacked the moment its head was raised. On 

 one occasion when sitting on the beach of Damba I saw 

 a Varanus come out from the forest and walk slowly 

 past me. Tse-tse were around me in considerable num- 

 bers, but the Varanus was evidently equally attractive, for 

 several went to it and began to feed, as was evidenced 

 by the repeated movements it made to scratch them off 

 with its hind legs. 



Crocodiles are also an extremely important source of 

 food, and their habits favour this, for like Varanus they 

 often lie for long periods at the water's edge. Measurements 

 of the blood corpuscles in wild flies seemed to indicate 

 that nearly 41 per cent, of the reptilian blood is from 

 this source. It appears at first sight rather remarkable 

 that the horny plates should prove no impediment to 

 the proboscis of the fly ; yet Fiske and I on Kimmi in 

 1914 watched closely for half an hour a small crocodile 

 which the natives had caught and was tethered near the 

 water, and between 8-35-9-45 a.m. forty flies had fed 

 fully ! This figure did not include those that were 

 disturbed and did not feed to repletion. 



The sites chosen by the fly were carefully noted in each 

 case save two, and are indicated below : 



38 



It is seen that the fly was even able to penetrate through 

 the back ! 



