34 STRUCTURE OF THE LEPIDOPTEBA 



that a considerable number of the extremely delicate threads must 

 be necessary to hold it in position ; but, if you would like to know 

 how a very small and feeble caterpillar can manage to roll up a 

 comparatively large and rigid leaf, you must watch the little crea- 

 ture at its work. 



You need have but little difficulty in finding a willing worker, 

 for such caterpillars are extremely numerous. Take a few out of 

 their self-made homes, place them on a sprig of the food plant, 

 and you will soon have the pleasure of seeing one start its extra- 

 ordinary work. 



At first it spins a number of threads stretching from the edge of 

 a leaf to about the middle of the surface. These threads are not 

 tight by any means, and the leaf is, as yet, unchanged in position. 

 But now the little mechanic exhibits a tact that almost seems to 

 prove a knowledge of the principles of its art. Each thread in turn 

 is pulled at right angles at its middle, and then fastened by means 

 of the creature's spinneret. Each time this is done the edge of 

 the leaf is bent round a. tittle ; and when at last the cylinder is 

 completed, a number of other threads are stretched across from the 

 scroll to the flat part of the leaf to secure it firmly in its place. 



Many caterpillars are solitary in their habits : that is, they are 

 always found singly, whether walking, resting, or feeding. But a 

 large number of species are gregarious, living in dense clusters 

 either throughout their larval state or, perhaps, only while young. 

 In many such cases it is difficult or even impossible to find any 

 reason for this gregarious tendency — to discover any advantage 

 that the insects may derive from the habit. Many species, how- 

 ever, are true co-operators in the defence of their communities. 

 The caterpillars of such live in clusters, sometimes several scores 

 in each, and all help in the spinning of a complicated mass of silk 

 fibres, which, with the leaves and twigs they join together, form a 

 safe home in which they can rest, feed, or change to the chrysalis 

 state. In early summer hundreds of such caterpillar ' nests ' are 

 to be seen in many of our hawthorn and other hedgerows. 



Before closing our general account of the caterpillar we must 

 have a word to say about the breathing appai'atus, more especially 

 as in our future descriptions we shall freijuently have to mention 

 the colours and markings which surround the openings in its body 

 through which the air supply is admitted. 



If you examine the sides of the segments of a caterpillar, using 

 a lens if the insect is a small one, you will observe some little 



