398 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



long fills the hollow of the leaf (fig. 3.) A few caterpillars always 

 work on top of the structure, roofing it over with a smooth sheet of 

 web which is anchored along both edges of the leaf. The network 

 beneath soon becomes peppered with blackish grains of frass, show- 

 in«- that the appetities of the workers have already been attended to, 

 and, if we look, we are likely to see that one shift is now laid off 

 and is feeding on the surface of the leaf beneath the tent as in- 

 dustriously as the other is spinning and weaving above. As belated 

 members of the family hatch from the eggs they follow the trail of 

 the others to the web and join the crowd. 



In a day or so the edges of the webbed leaf become strongly rolled 

 upward, the hollow being entirely filled with web and perhaps the 



Fig. 3. — First web of the young caterpillars, spun over the upper surface of a leaf. 



whole leaf wrapped in a thin sheet of silk. A bridge is now spun 

 to a neighboring leaf or twig and the colony begins to spread out 

 over greater territory (fig. 4). If a second leaf is not directly 

 accessible from the first a few venturers explore the twig by Way 

 of the leaf petiole, leaving a trail of silk along their way which 

 guides others over the same course. Soon the stalk of another leaf 

 is discovered and the beginnings of a web are spun about it. Emi- 

 grants from the first leaf follow in increasing numbers and soon a 

 second is swathed in a thin web of shining new silk. Several leaves 

 may be thus individually webbed during the first few days of the 

 caterpillars' lives (pi. 1), but soon the spinning of a more pretentious 

 structure is undertaken, which will inclose a group of leaves in its 

 gossamer walls. The earlier leaves are by this time dying and turn- 

 ing brown and their webs are mostly deserted, though a few cater- 



