Bagworms and Webworms
Bagworms vs. Fall Webworms
With the long hot days of summer upon us, many residents in the Town of Flower Mound are beginning to notice bagworms and fall webworms afflicting trees through out town. Even though both insects have the word worm as part of their common name, they are actually caterpillars.

Bagworms can be seen hanging from the twigs of a variety of trees and shrubs. They are recognized by the distinctive 1.5 to 2 inch long spindle-shaped cocoons that they make. The cocoons are made from a combination of silk that they spin, along with leaf, twig and bark material from the host tree that they are feeding on. A wide range of broadleaf and evergreen trees and shrubs serve as hosts for bagworm species. These include arborvitae and other ornamental conifers, box elder, cedar, cypress, elm, fruit and nut trees, juniper, live oak, locust, maple, persimmon, pines, salt cedar, sumac, sycamore, wild cherry, willow, and many other ornamental plants.

This list is pretty extensive and includes many trees found within the Town of Flower Mound. A host plant will have an increase in bagworms each year because the females don’t fly. The bagworms may become abundant enough in some years to completely defoliate their host plant. This is a real concern for evergreen trees (those that retain their leaves through winter) and might eventually lead to premature death of the host plant. Deciduous trees are better able to cope with the damage left by bagworms because they have the ability to generate new leaves to replace those that are been damaged by bagworms during the same growing season. Dispersal of bagworms to new host plants occurs when young caterpillars hanging from silken threads are spread by wind. This process is called ballooning. Caterpillars can also be spread by birds.

There are multiple methods of treatment for bagworms but the Town of Flower Mound advocates those that are the least harmful to the environment. The best control method would be to remove the cocoons hanging from tree limbs during the fall, winter and early spring time, before the eggs hatch. Some of the cocoons will contain a female bagworm and/or 300 plus eggs. When many small bagworms are present and feeding, an insecticide may be needed to prevent serious damage. The best time to apply an insecticide is while the larvae are still small (less than 1/2-inch long), usually in May to early June for North Texas. Small larvae are more vulnerable to insecticides, and feeding damage is relatively minor. Carefully inspect susceptible landscape plants. Young bagworms are hard to see at first so look closely for the small, upright bags during the spring months. They will have the appearance of tiny ice cream cones made of bits of plant material.

Fall webworms are another caterpillar that may be confused with bagworms. Fall webworms are most readily found in pecan trees throughout the town. They also have been observed in elm, cottonwood, mulberry, and redbud trees.
The female moth will lay a cluster of a few hundred eggs on the underside of the leaves of a host plant in the spring and the eggs hatch approximately one week later. After hatching, the larvae immediately begin spinning silken webs for protection from predators while they are feeding. The caterpillars will skeletonize leaves so that only the veining structure remains. The webs initially start at the tip of branches and can eventually extend all the way down to the trunk of a tree.

The best way to deal with fall webworms is to physically break open the webs and allow birds and other predators to eat the caterpillars. This can be done with handheld tools if the webs are lower in trees, or with a high-pressure water hose for those webs in the upper parts of trees. This process may need to be repeated several times throughout the growing season, but can be effective at controlling webworm populations in individual trees. Pesticides can also be used to control fall webworms. Consult with a certified arborist if this type of treatment is desired.

Additional information about bagworms and fall webworms can be found at the following websites:
If you have any questions or need additional information, please contact the Town of Flower Mound’s Environmental Services Division at 972.874.6352.

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