The tent of the eastern tent caterpillar is among the largest built by any tent caterpillar. The tents are constructed in the crotch of the host tree and are typically oriented so that the broadest face of the structure faces the southeast, taking advantage of the morning sun. 

The caterpillars initiate the construction of a silk tent soon after their eggs hatch.  In the video above, silk accumulates in the crotch of the tree as the caterpillars move back and forth forming the beginings of the tent.  Once established, the caterpillars typically aggregate at the tent site for the whole of their larval life, expanding the tent each day to accommodate their increasing size.  The tent is essential to the success of the early instars, greatly facilitating their ability to thermoregulate on cold spring days.

The tent has openings that allow the caterpillars to enter and exit the structure.  Openings are formed where branches jut from the structure but are most common at the apex of the tent.
Caterpillars continue to expand their tent until they enter the last phase of their larval life.  The sixth-instar caterpillar conserves its silk for cocoon construction and adds nothing to the tent. The tents appears multifunctional.  They facilitate basking, offer some protection from enemies, provide for secure purchase, and act as a staging site from which the caterpillars launch en masse forays to distant feeding sites. The elevated humidity inside the tent  may facilitate molting
Shelter Building
The caterpillars typically add silk to the structure at the onset of each of their daily activity periods.  Silk is added directly to the surface of the tent as the caterpillars walk back and forth over the structure. The silk is laid down under slight tension and it eventually contacts, causing the newly spun layer of silk to separate from the previously spun layer. The tent thus consists of discrete layers of silk separated by gaps within which the caterpillars rest.

In this time lapse video, the arrow marks the location on the outer layer of silk at the beginning of four descrete bouts of en masse spinning occuring at approximately 6 hour intervals.