Home gardeners often find their trees under attack by caterpillars. These pests feed on tree leaves and many are capable of defoliating entire trees when heavy infestations occur. Healthy trees are usually able to stand several defoliations before they die from infestations of caterpillars. Many caterpillars attack trees under stress from injury or drought.
Bagworm caterpillars are common pests of cedar, juniper, arbor vitae, spruce and pine. These caterpillars are known for the spindle-shaped bags they make and place on host tree branches. Bagworms make these silky, brown bags from silk and plant debris and live inside the bag enlarging it as they grow. Bagworms typically feed on host trees for a period of six weeks. Female bagworms lay several hundred eggs inside the bag before she dies. Another caterpillar responsible for defoliation of many trees is the eastern tent caterpillar. These caterpillars prefer wild cherry, crabapple, apple, peach, plum, pear, cherry, Hawthorne and maple. Eastern tent caterpillars place shiny, black egg sacs on the branches of infested trees that usually hatch around bud break.
Young bagworm larvae damage the needles and leaves of host trees through feeding but damage from immature larvae is not usually severe. Older bagworm larvae are capable of stripping entire trees of their needles or can consume entire plant leaves during a single feeding. Trees suffering from severe defoliation or that are infested several years in a row, often die from infestation. Eastern tent caterpillar larvae are black and hairy and feed on host tree leaves. These caterpillars increase the size of their tent as they feed, until it reaches a foot or more in length. Eastern tent caterpillars feed on host trees for approximately four to six weeks before wandering from the host tree.
Most caterpillars do not infest healthy trees. Trees under stress from drought or those suffering from pruning injuries or sunscald are most likely to suffer from caterpillar infestations. Prune trees in close proximity to caterpillar-infested trees to prevent caterpillars from migrating to other plants and trees.
Removing caterpillars from your tree is easily done by hand. Hand-pick caterpillars from your tree and place them in a bucket of soapy water to kill them. Be sure to remove the brown silk bags and large tents to prevent new larvae from hatching. Removing caterpillars and egg sacks is most effective if done during the fall, winter or early spring before eggs hatch and new larvae emerge. Trees suffering extensive damage or repeated defoliation may require insecticides to control caterpillars. Choose a product with the active ingredients malathion, carbaryl or methoxychlor for best results.