The Life of the Caterpillar 



I see two reasons. In the first place, they 

 are hairless; and a brusjilike coat may well 

 be indispensable to the collection of the virus. 

 In the second place, far from lying in the 

 tilth, they live above the soiled stratum, being 

 largely separated from it by the bed of leaves, 

 which is renewed several times a day. Despite 

 crowding, the population of a tray has no- 

 thing that can be compared with the ordinary 

 habits of the Processionary ; and so it remains 

 harmless, in spite of its stercoral toxin. 



These first enquiries lead us to conclusions 

 which themselves are very remarkable. All 

 caterpillars excrete an urticating matter, 

 which is identical throughout the series. But, 

 if the poison is to manifest itself and to cause 

 us that characteristic itching, it is indispensa- 

 ble that the caterpillar shall dwell in a com- 

 munity, spending long periods in the nest, a 

 silken bag laden with droppings. These fur- 

 nish the virus; the caterpillar's hairs collect 

 it and transfer it to us. 



The time has come to tackle the problem 

 from another point of view. Is this for- 

 midalle matter which always accompanies the 

 excretions a digestive residuum? Is it not 

 rather one of those waste substances which 



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