180 A NATURALIST IN HIMALAYA 



each new arrival, possibly examines each burden as 

 to its fitness for the store, or identifies each worker 

 before it gives admission in order to prevent the 

 intrusion of a stranger. Sometimes, as though in 

 doubt, it pursues a worker into the interior of the nest. 

 It pays less attention to the departing wasps ; it seems 

 to care little whether they leave empty or carry a 

 little load of earth from the interior of the tunnel. 

 As one ant knows every other in the nest, so it may 

 be that this sentinel knows all others in its own 

 community, and is placed there to prevent a stranger 

 from entering the precious store. 



Another species of wasp, Polistes hebr&us, adopted 

 a method similar to that of Vespa of vibrating its 

 wings to lower the temperature of its nest. A colony 

 of these wasps had built a large nest in a rose tree 

 close to the verandah of my bungalow. The nest 

 consisted of a circular comb hanging from a central 

 stem and built of a single layer of hexagonal cells, all 

 closed above and with the open ends directed down- 

 wards. I noticed that in their efforts to cool their 

 larvae they acted much like the Vespa. The nest was 

 so situated that, throughout almost the whole day, it 

 was shaded from the sun by the surrounding trees ; 

 but, in the early morning, the sun, while still low on 

 the horizon, could peep below an overhanging shrub 

 and fall on one margin of the nest. As a consequence 

 the cells at this margin became uncomfortably warm 

 and gave the wasps much trouble in their labours to 

 keep them cool. It was instructive to watch a worker- 

 wasp creeping about over the heated cells, testing 

 each one with its sensitive antennae. As soon as it 

 discovered a cell which it considered too warm for the 



