190 A NATURALIST IN HIMALAYA 



its nest beneath an overhanging ledge on the face of a 

 chff composed of a fine conglomerate. Now a nest of 

 smooth, pale mud lying against the stones of this cliff 

 would be very conspicuous, and I felt sure that the 

 wasp must have understood this. For it had covered 

 the whole surface of its nest with pebbles so that it 

 was very difficult to differentiate the nest from the 

 underlying conglomerate. The rounded stones, with 

 which the wasp had studded its nest, were compara- 

 tively large, many over a quarter of an inch in diameter, 

 and it seemed surprising that the insect could carry so 

 substantial a load. 



I was deliohted when I discovered this little nest 

 of pebbles, for I felt certain that I was looking at a 

 beautiful instance of harmonization, so invisible did 

 the nest become by blending with the conglomerate 

 cliff I wrote in my journal that "this was one of the 

 prettiest examples that I had seen in the life of insects 

 of a plastic instinct employed to so useful a purpose, 

 for I have no doubt that it was a gain to the species 

 to render its nest invisible through harmony with its 

 surroundings by covering it with a layer of the same 

 little water-worn pebbles that went to build up the 

 conglomerate cliff" 



But I was making a grievous error. These nests 

 were not common, and for some weeks I could find 

 no others than those on the conglomerate cliff, until 

 one day I discovered a nest of four cells implanted on 

 a smooth slab of slate. I was surprised, for I had 

 felt almost convinced that the covering of pebbles was 

 an example of a wonderful protective instinct and that 

 a wasp constructed a nest of pebbles only against a 

 pebbly cliff, yet, there before me was a nest studded 



