120 THE WONDERS OF INSTINCT 



But a second caterpillar steps on the slender foot- 

 board and doubles it with his thread ; a third trebles it ; 

 and all the others, however many there be, add the sticky 

 spray from their spinnerets, so much so that, when the 

 procession has marched by, there remains, as a record of 

 its passing, a narrow white ribbon whose dazzling white- 

 ness shimmers in the sun. Very much more sumptuous 

 than ours, their system of road-making consists in up- 

 holstering with silk instead of macadamizing. We 

 sprinkle our roads with broken stones and level them by 

 the pressure of a heavy steam-roller ; they lay over their 

 paths a soft satin rail, a work of general interest to which 

 each contributes his thread. 



What is the use of all this luxury? Could they not, 

 like other caterpillars, walk about without these costly 

 preparations? I see two reasons for their mode of pro- 

 gression. It is night when the Processionaries sally forth 

 to browse upon the pine-leaves. They leave their nest, 

 situated at the top of a bough, in profound darkness; 

 they go down the denuded pole till they come to the 

 nearest branch that has not yet been gnawed, a branch 

 which becomes lower and lower by degrees as the con- 

 sumers finish stripping the upper stories; they climb up 

 this untouched branch and spread over the green needles. 



When they have had their suppers and begin to feel 

 the keen night air, the next thing is to return to the 

 shelter of the house. Measured in a straight line, the 

 distance is not great, hardly an arm's length ; but it can- 

 not be covered in this way on foot. The caterpillars have 

 to climb down from one crossing to the next, from the 



