Fall Webworms or Bagworms?

Fall Webworms or Bagworms?

There is often confusion as to which insect pest is called webworms and which is called bagworms. Some think that bagworms and webworms refer to the same insect pest. There are three different insects on trees where the names are sometimes confused or interchanged. The three insects are fall webworms, bagworms, and Eastern tent caterpillar.

Fall webworms are sometimes mistakenly called bagworms. Fall webworms are the webs you can see at the ends of branches on many trees during the fall season. Fall webworms are a mass of webbing at the end of tree branches. The webs contain many tiny, hairy caterpillars. Most often the fall webworm is found late summer into the fall on pecans, sourwood, and persimmon although they feed on over 600 species of trees and shrubs. Fall webworms can be easily destroyed or disrupted by pulling down webs that are within reach with a stick or pole. Pulling down the webs exposes caterpillars to birds and wasp. Carbaryl (Sevin) can be used to spray webs within reach. When using an insecticide for fall webworms, spray the foliage closest to the web mass. Spraying the web itself does not give good contact with the caterpillars. If the webs are not within reach, do not worry because although they are unsightly they usually do not harm the tree’s overall health.

Bagworms are small (1/8″ to 2″ long), diamond-shaped silk bags. The worms make and live inside the bags. The bags can be easily missed because the worms camouflage the bags with parts of the tree. These bagworms are often found on arborvitae, Leyland cypress, and juniper. The easiest way to control bagworms is to pick or clip them off of the tree limbs and drowned the bags in soapy water. If using insecticides, they need to be used in June or early July when the bagworms are small or else the insecticides will not penetrate through the bag and reach the worm. Insecticides that can be used to control bagworms include:  B.t. (Dipel), carbaryl (Sevin), and malathion.

The Eastern tent caterpillar is often called webworms, but there are two major differences between the two insects. The Eastern tent caterpillar forms webs in the center of a tree’s canopy in late-spring into summer, while the fall webworms form webs at the end of tree branches in late-summer into the fall. The Eastern tent caterpillars are black with a gold or white stripe down the back. Eastern tent caterpillars are most often found on wild cherry, crabapple, and apple trees but many other kind of trees are occasionally infested. Trees that are defoliated for several years by Eastern tent caterpillars may decline noticeably. Because the Eastern tent caterpillars spend the winter inside the egg masses, one effective method of controlling the caterpillars is to remove and destroy the egg masses before the caterpillars hatch. If the caterpillars have already hatched, the tents can be pulled down with a sick and the caterpillars crushed. Carbaryl (Sevin) is labeled for controlling Eastern tent caterpillar.

It is important to note for safety reasons that it is not recommended to use fire to destroy fall webworms or Eastern tent caterpillars as a fire can set up an extremely dangerous situation. Fire may get out of hand and destroy the tree, endanger the person, and nearby properties.

Maybe this will reduce some of the confusion on what insect pests are called bagworms, webworms, and tent caterpillars. All three are common on many trees in the landscape. By knowing how to tell the difference between the three, one can determine when to take the best control measures.

Recommendations for the use of agricultural chemicals are included in this article as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this article does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical.

 Jessica Strickland is an agriculture extension agent, specializing in horticulture for North Carolina Cooperative Extension in Wayne County.