160 A NATURALIST IN HIMALAYA 



the bird missed its prey and the butterfly looked to 

 all appearances dead. I went to pick it up, thinking 

 that it must be either dead or injured since it did not 

 rest upright, but rather lay on its side like a leaf in 

 the dust. However, it was far from really dead. I 

 had no sooner touched it than it raised itself from the 

 ground, opened wide its wings and flew uninjured 

 away. This seemed a good illustration of the principle 

 of feigning death ; there was no doubt that the Libythea 

 was well aware of its danger and saved its life by 

 adopting the simple ruse of hurling itself to the 

 ground, where it lay motionless pretending that it 

 was dead. 



I have mentioned these instances to show how 

 general is this instinct both amongst spiders and their 

 prey. Whatever may be its origin, it is a very real 

 and valuable behaviour, and the fact remains that the 

 attitude adopted by the species when feigning death 

 is the same as that assumed when the spider or insect 

 is actually dead. 



Before leaving the Hippasa I may mention a few 

 physical properties of the webs of spiders that some- 

 what interested me. The first was the remarkable 

 power possessed by the web of the sheet-building 

 spiders in preventing evaporation in the air beneath 

 it. One species of this tribe of spiders used to con- 

 struct its sheet amongst the rank grass or over hollows 

 in the sand. During the night a deposit of dew used 

 to form on the under surface of the web, and one 

 would think that the warm sun would quickly evaporate 

 the cluster of dewdrops that hung from the silken 

 snare. But the sun did not seem to have the power, 

 for the drops remained. I did not take much notice 



