Types of Worms in Outdoor Trees

Worms attack outdoor trees during the better portion of the year. Even if a tree is hardy enough to withstand worm damage, the effects of worms building homes and thriving on the tree's foliage can make for an unattractive lawn ornament. Knowing which types of worms reside on which tree species can be instrumental in combating the problem and in applying the proper insecticide or worm repellent.

The fall webworm looks like a caterpillar with long, spiky hairs poking out from all sides of its body. This worm derives its name from the massive, spiderlike web it spins around tree leaves. According to Pennsylvania State University, the webworm lays eggs underneath the leaves of trees like hickory, walnut and cherry, which gives the resulting larvae convenient access to food upon hatching. These worm babies are responsible for spinning a web on tree branches, which allows them to eat the leaves down to nothing in safety and comfort. While this activity might not actually kill the tree, it does make its leaves far less attractive.

The orange striped oakworm is actually a caterpillar with a black body and two orange stripes spanning its body's length. According to the Maryland Department of Agriculture, these worms target white oak and red oak species for food. Like the fall webworm, the orange striped oakworm also lays eggs beneath the leaves; when the larvae hatch, they feed from the oak tree leaves, leaving large, nibbled areas or leaf skeletons. Gardening expert Walter Reeves, of walterreeves.com, says the orange striped oakworm's lifespan is short, so unless they are causing significant damage, insecticide might not be necessary.

The catalpa sphinx, also referred to as the catawba worm, incurs serious damage to ornamental lawn trees, according to Auburn University's Department of Entymology. These worms, which are black-bodied and bear a sharp horn near their back ends, are typically present through spring and summer, though their season might extend to fall. The catalpa mother lays eggs in the typical manner, underneath tree leaves; after the larvae hatch, they wreak havoc by eating most or all of the tree's foliage.

Bagworms generally target species of evergreen trees. According to the University of Kentucky College of Agriculture, juniper, pine, spruce and cedar trees are the bagworm's most desirable victims. A bagworm caterpillar forms its larvae in brown, bag-shaped cocoons, which resemble a long mop or head of hair. Once the larvae hatch, they munch on evergreen needles and other plant foliage. Unlike other worm pests, which only deform a tree and don't actually kill it, bagworm activity is sometimes lethal to the tree, especially if allowed for several years.