Tent caterpillars are so named because they construct a communal tent of densely spun silken threads, most often in branch crotches. The tents are used for caterpillar protection, resting and molting. 
Tent caterpillars feed on various types of trees depending on the type of insect. Cottonwood, plum, chokecherry, willow and aspen are most oftenaffected. The insects usually feed at night, chewing on leaves as they forage about. They can completely defoliate a plant.
Natural controls such as parasites, disease and birds help keep most populations managed without further treatment.
Physically removing the insects/tents or spraying with Bacillus thuringiensis, spinosad, pyrethrins, or carbaryl can control tent caterpillars. Timing of any spray should correspond with the caterpillars still being present in the tents and on the tree.
For more information, see the following Colorado State University Extension fact sheet(s).
