^656 0. B. HAEDENBERG. 



infestation are unfavourable to a continued existence of the 

 species therein, and this travelling instinct to a certain extent 

 prevents the larvae from settling in the same spot where their 

 pregenitors have been bred. 



B. Agents in the distribution. — As the distribution 

 of the species is not effected by the flight of the adult, like 

 in the majority of Lepidoptera, the period in the life of 

 the insect when this all-important process takes place has 

 been transferred from the adult stage to the first instar of 

 ■the larval life. In this, except for offering opportunities to 

 facilitate this distributiou, the larva plays an entirely passive 

 role, and is dependent on external agencies. These agents 

 .fall under three heads, each responsible for a distinctive type 

 of infestation of a new area. 



(a) Wind. — By far the principal agent, favouring distri- 

 bution over wide areas, is the wind. Due to their exposed 

 position on the edges of plantations or on the tips of the trees, 

 brushwood, stumps, etc., the larv« are easily accessible to any 

 air currents, while their lightness, caused by the long silken 

 thread, allows of their being readily picked up and cai*ried 

 for considerable distances. An analogy of this procedure is 

 found in the well-known example of the so-called " Balloon 

 Spiders." During the hatching period of the egg (the later 

 part of August and until the beginning of October) the 

 climatic conditions in this country are such that heavy wind- 

 storms are an almost daily occurrence. The wind rises about 

 nine o'clock in the morning and, usually, dies down towards 

 evening. These wind-storms are often characterised by the 

 presence of eddies, and the young bagworms are either driven 

 before the wind or carried up in the vortex to higher strata. 

 In this way they may be carried for miles, and when the 

 wind dies down and the air becomes calm the bagworms 

 slowly descend and fall literally out of the sky on trees, grass, 

 and other objects indiscriminately. Countless numbers perish 

 by landing in places unsuitable for their existence, but such 

 as happen to alight on one of their many food-plants have a 

 •chance to attach themselves and start feedino-. The Avriter 



