Most of us are familiar with the bagworm, Thyri-dopteryx ephemeraeformis, whose baglike case eventually reaches a length of 1-1/4 to 1-1/2 inches. At this time, they are much smaller and can be effectively controlled as they feed on Eastern red cedar, other junipers, spruce, arborvitae, and various other coniferous and deciduous trees.
A smaller species, Solenobia walshella, occurs sporadically in Illinois. It has been somewhat consistent in its appearance in the Rockford area. This species produces a case similar to the bagworm’s, but it only reaches a length of about 1/2 inch. It apparently feeds as a caterpillar on the lichens growing on the trunks of balsam fir, white spruce, tamarack, black spruce, red spruce, Eastern hemlock, and Eastern white pine. When fully grown, it tends to migrate to other locations, commonly ending up in large numbers on the sides of houses where they are difficult to remove. Landscapers may get blamed for not controlling the pest, but this species is not really a pest of trees, although it feeds there.