106 ANIMAL PARASITES. 



skin for the first time towards the end of May by rubbing 

 against the uneven bark of the oak. They are now of from one 

 third to one fourth of an inch long, of a grey colour, distinctly 

 showing twelve segments, and on the top of each segment a 

 black shield with very short, velvet- like hair of a peculiar lustre. 

 The large hairs are ranged in from two to three bunches on each 

 segment, having lower down on their sides eight spiracles and 

 eight pairs of legs. 



During the time of the casting off of the skin, the grey cater- 

 pillar becomes yellowish-brown, lustreless, stronger, but lazier. 

 The caterpillars mostly gather where a branch withers, and 

 attach themselves so firmly by spinning a cocoon, that cater- 

 pillar and bark seem one. The cocoon is thin and transpa- 

 rent, and attached to its inner part is the cast skin. These 

 caterpillars have quite the appearance of the former, and begin 

 their wanderings afresh a caterpillar leading each troop, having 

 attached to its tail other caterpillars and so on. They grow now 

 very large, and collect together at the end of June or the begin- 

 ning of July in increasing numbers. The caterpillars, placing 

 themselves side by side or one above the other, cast their skin a 

 second time and wander again, leaving threads behind on the 

 path of their emigration. They are now excessively voracious, 

 and deposit largely the matter which is so obnoxious to men and 

 animals. Being now more than one inch in length, and very 

 strong, they are seen to make long journeys, annexing all smaller 

 troops which they meet on their way. They gather at last on 

 the trunk of a thick tree, placing themselves side by side to 

 the extent of a man's hand, and then one above another in three 

 or four rows, after which some of the larger caterpillars are seen 

 to creep from underneath and spin all round the heap. The 

 spinners are relieved by others at regular periods, and from six 

 to eight caterpillars may be seen on the cocoon, which is usually 

 fastened to the sunny side of the trees, rarely to the stormy and 

 northern side, at a considerable height close to the twigs, and 

 where a twig or branch is decaying. A hole is left in the 

 cocoon for the passing in and out of the caterpillars, which is 

 always guarded by several large caterpillars. These guards allow 

 only larger caterpillars to pass, preventing all smaller ones which 

 may happen to follow from entering, and appointing for their 

 use a separate place close to the nest, from whence they are led 

 by a larger caterpillar on new excursions to young leaves, the 



