This is the time of the year when bagworms, webworms and tent caterpillars start appearing on trees and shrubbery. All can be serious pests, but by taking preventive measures, they can be controlled satisfactorily.

All are easy to identify: the bagworm’s bag resembles a small Christmas tree ornament hanging from a limb, and the larvae (caterpillar) begin to emerge from their silken bags in which they have over-wintered from late May to mid-June. The webworms and tent caterpillars are the larvae of several different species, but all make their presence known by spinning web nests, which can be  numerous, unsightly and esthetically detracting within a landscaped area. Some of these webworms and caterpillars are known as the fall webworm, walnut caterpillar, yellownecked caterpillar, eastern tent caterpillar, catalpa sphinx and poplar tentmaker.

The bagworm is more likely to be found on arborvitae, red cedar and other juniper species, although they reportedly feed on 128 plant species. The fall webworm is often a serious pest of many species of forest, shade, fruit and ornamental trees (except conifers) throughout the United States.  Walnut caterpillars feed on a variety of deciduous trees, but prefer walnut, butternut, pecan and hickory.  Yellownecked caterpillars also feed on a variety of trees, including birch, elm, maple, walnut, oak, honeylocust, hickory, sumac, crabapple, and cherry. The eastern tent caterpillar's preference of host trees is wild cherry, apple and crabapple, but will occasionally feed on forest and ornamental trees such as ash, birch, maple, oak, poplar, cherry and plum. The catalpa sphinx only feeds on catalpa trees, and the poplar tentmaker feeds on foliage of various species of poplar and willow.

What can be done to rid your trees and shrubs of these serious pests? Proper timing is very important, because insecticidal sprays are not very effective on either bagworms, webworms or tent caterpillars after the bagworms have matured and attached themselves to branches, or the webworms and tent caterpillars have spun their webs.

For bagworms, some species of birds, such as sapsuckers and woodpeckers are able to tear open the bags and feed on the larvae, and can control small populations, but for more severe infestations, more drastic measures need to be taken.

The cheapest method of controlling bagworms on small trees and ornamentals is to handpick the bags. Pick off all bags and destroy them. For larger plants where handpicking is not practical, they can be controlled by spraying with an insecticide, but this must be done in the spring as soon as the eggs hatch and the small larvae begin emerging from the over-wintering bag. Spray applications are most effective while the larvae are still small.

Webworms and tent caterpillars can be controlled naturally by searching the foliage and branches for newly developing nests or tents, and pruning off and destroying infested leaves and twigs. Removal of the silken tent of the eastern tent caterpillar cannot be done by pruning because the tents are often found on the fork of a major scaffold limb where pruning would not be desired. However, during the night or on cloudy, overcast days when the caterpillars are in their tents, the tents can be scraped off the trees and destroyed.

For larger trees where it is impractical to search the foliage, it is best to apply an insecticide, which needs to be done as soon as larvae appear.