338 THE AILANTHUS SILKWORM AND THE AILANTHUS TREE. 



they remain inactive from twenty-four to forty-eight hours, according to 

 the temperature. Before this crisis arrives, they cover the under part of 

 the leaf on which they are with an invisible gummy substance of threads- 

 of silk, and they fix so solidly their membranaceous feet that the old skin 

 remains adhering whilst they pass on. 



The existence of these caterpillars, like those of the Mulberry Silkworm, 

 is divided into five stages. The first is the interval between their birth 

 and the first change ; the second is that between the first and second 

 change ; the third is between the second and third ; the fourth, that from 

 the third to the fourth ; the fifth, that of the fourth change till the forma- 

 tion of the cocoon. The caterpillars have a different colour and shape in 

 each of these stages. Thus, during the first, as I have before said, they are 

 yellow-coloured with a black spot down the belly, independently of black 

 tubercles. During the second change their body is about 4 or 5-tenths of 

 an inch long. They are still yellow, with head tubercles and segments 

 quite black. At the third crisis the caterpillar is from 6 to 8-tenths long, 

 and soon becomes quite white. At this stage there comes all over their 

 body a waxy secretion, forming a sort of white flour, destined to protect- 

 the worm against rain and dew, as water cannot fix on it. At the fourth 

 stage it attains the length of | to 1 inch. Its body is first white ; then it 

 becomes gradually green, with tubercles of the same colour ; and soon the 

 head, the feet, and the last segment become of a golden yellow. There are 

 always black points upon the segments or rings of the body and the floury 

 secretion. At the fifth stage the emerald green colouring is the same, but 

 more intense, and the extremities of the tubercles become of a marine blue. 

 The caterpillar is then from lj to lj inch long, but it grows rapidly, and, 

 according to the abundance and quantity of the food, it attains the length 

 of from 2-| to 3 inches long. 



Arrived at this stage, it begins to eat less and gradually becomes of a 

 yellowish-green. It begins the cocoon by fixing two or three leaflets firmly 

 to the main stem with its silk, so that it may be secure at the fall of the 

 leaf in the beginning of the •winter. 



In weaving its cocoon this worm does not proceed like the Mulberry 

 Silkworm, because it makes an elastic opening for the exit of the moth. 



In working, the caterpillar takes from time to time a little repose, but 

 this only lasts a few seconds. From time to time also, after having placed 

 a number of zigzags of thread, it stops and puffs itself out, as if to push 

 out the sides and make the necessary room. When it works from the side 

 of the opening it makes much longer movements, and places the thread in 

 a longitudinal way, advancing it to the extremity of the opening, cement- 

 ing one thread to another, and returning parallel to the first thread. 

 During all this while its antena? are at work, as well as its mandibles. 

 These seem to serve as polishers, for they neither bite nor cut any part of 

 the w r ork. The threads that form the opening of these cocoons are not cut 

 but simply turned and laid one over another. The cocoons of the 

 Ailanthus worm are of an elongated form, of more or less pale and grey 



