SOUTH AFRICAN BAGWORMS. 655' 



and also the outer branches of such trees as form the out- 

 side edge of a block. It also causes the larva to feed on the 

 young tips of the foliage, as long as any leaves are being 

 produced. Toward the end of the feeding period we find a 

 reversal of this instinct ; the larva now prefers a more con- 

 cealed spot in which to pass its pupal stage. 



(b) The extensive use of the spinning glands. — 

 While in the majorit}' of caterpillars the spinning glands 

 are not brought into full use until the time for pupation 

 approaches, when the manufacture of a cocoon becomes 

 necessary, we find here that one of the first acts of the young 

 larva is the spinning of a long silken thread. By means of 

 this it descends from the parent bag, and, att.aching the 

 tliread to a twig or branch, a sheet of webbing is made on 

 which the larva travels up and down. This webbing is 

 extremely light and is disturbed by the slightest air-current. 

 This same webbing is produced when the larva has reached 

 the exposed parts of the trees or brushwood, and the area 

 where the larvas have been hatching by the thousands looks as 

 if covered with a layer of spider-web. In later instars the 

 spinning glands are almost exclusively used in the construction 

 of the bag, and only when the food-supphMnins short does the 

 caterpillar again construct long threads of silk by means of 

 which it descends, and either reaches the ground and crawls 

 to another tree, or is swayed by the wind to the branch of a 

 neighbouring tree to Avhich it then attaches itself. 



(c) The meandering instinct. — As a third additional 

 provision to safeguard the distribution of the species we 

 have on the part of the young larva the peculiar instinct 

 that it will not feed during the first few days of its existence. 

 It appears that its desii^e for a certain amount of travelling- 

 has to be satisfied befoi'e it will settle down to feed and 

 construct its dwelling. This increases the difficulty of rearing 

 the specimens in captivity from the egg, as the majority of 

 the minute caterpillars leave the fresh young wattle twigs 

 supplied to them and start travelling about. As will be 

 shown later, the conditions in a plantation after a heavy 



