As fall approaches, you’ll start to notice clumps of webs popping up in the branches of your trees. There are two pests that become super active in late August and early September, Bagworms and Webworms.  And they leave behind the ugly, yet not super harmful, signs of their work. Let’s distinguish the two first.

Bagworms 

Bagworms (Thyridopteryx ephemeraeformis) create a silky nest, about the size of a pine cone. It’s typically covered in bits of foliage from the host tree. They primarily nest in evergreens, such as Leyland cypress, spruce, pine, arborvitae, and juniper trees. But they can also be found in deciduous trees. They create a significantly more adverse impact on evergreens than deciduous trees, including complete defoliation which can kill the tree. 

They feed on the tender leaves of evergreens. You may notice branches die and tips dropping off. If the bagworm destroys 80% of the foliage or more it can easily kill the tree.

The caterpillars are hatched from eggs in the spring and spin a fine thread-like web to travel to adjacent trees and begin forming their cases. They spend much of their time in their case through the summer and emerge as adults in the late summer/early fall to mate. In their adult form they are ashy-black-bodied moths with transparent wings. 

Treatment for Bagworms.  The best approach to getting rid of bagworms is to remove them by hand. They can be crushed, or dropped in a bucket of soapy water to kill the caterpillar inside. Application of an insecticide is also an option but application must be timed correctly.

 

Webworms

Webworms (Hyphantria cunea) form unsightly masses of webbing in the ends of tree branches. They occupy deciduous trees, primarily oak, elm and maples. The webworm spins these web nests and spends most of its time in it where it’s safe from daytime predators, and emerges to feed at night. The webworm feeds on the leaves of deciduous trees, but typically doesn’t cause enough destruction to hurt the tree, as the leaves that are fed on will naturally drop from the tree in fall anyway. It will expand its web nest as it grows. 

Webworms are native to the United States and therefore are prey to many types of predators. They emerge as adults in the Fall. The adults present as mostly white moths with black or brown speckles on their wings; They have hairy front legs and a bright yellow/orange patch on its back.

Treatment for Webworms. To removes a nest, take a stick or broom handle and break up the webbing. Even if the caterpillar isn’t killed in this action, it is now exposed to natural predators. It is not necessary to trim the branches attached to the webbing. And certainly, do not set the web on fire. Light insecticide treatment is an option but it must be applied in such a way to penetrate the web nest.

 

If you have additional questions about possible infestations of your trees, please contact us. We offer complementary tree assessments to identify problems in the trees in your yard. Locally owned and operated from Glen Arm, MD, we provide tree service to northeastern Baltimore County and western Harford County.