A common sight along our country roads for the past month has been sophisticated webs at the ends of tree branches that glow like lumanarias when the sunshine hits them at the perfect angle. Many folks say they are created by bagworms, but real bagworms do not create these kinds of webs. Other folks call them tent caterpillars, and Eastern tent caterpillars do create similar webs, but in the spring and at crotches in fruit trees mostly, not at the ends of branches as we are seeing in late summer and early autumn.
What we are seeing is handiwork of the larvae of a native moth, Hyphantia cunea, commonly known as the fall webworm. The small moth is native to the eastern United States and has a wingspan of about 1.5 inches. Females are white and males might have black or brown spots on their wings.
Webs appear in August and last through September or early October. Their favorite host trees are pecans, persimmons, black walnuts and hickories, but in robust years they will feast on other hardwoods such as sycamores, birches and redbuds. In Virginia, they are a nuisance to hops’ growers.
Adriane Barnes of the Arkansas Forestry Commission states, “The caterpillars create silken tents that keep them safe while feeding on leaves. These webs are on the ends of branches, which can be easily pruned out.” An exception, of course, is when the web is toward the top of a 30-foot hickory tree.
The larvae begin tent-making in August with a small web around a leaf or two toward the end of a branch. It is a remarkable example of a community working together. As they are hungrier for more leaves, the larvae expand or combine their tents. The webs are three-dimensional in that they not only surround an area of the tree but also provide pathways across the open space from one branch to another. Interested observers can watch some larvae feed, others hike out across the web to the other side, while others even worm their ways up and down the trunk. Maybe they are scouting for fresh territory. The backs of the segmented hairy larvae are marked by alternating bands of dark gray and light reddish-brown, their heads sort of orange. Underneath they are yellowish.
In lower branches, a homeowner can use a tool to poke holes in the web hoping birds or predator insects will graze on the army of larvae inside. Using a cultivator to rake the tents off lower branches will help temporarily, but industrious webworms rebuild tents within a few days.
For observers who find them suddenly appearing on trees around the home, Barnes states, “Don’t get too concerned – this small creature is not considered a ‘forest pest’ because it rarely kills the host tree. It is, however, unsightly, and occasionally can cause damage to pecan groves.” The defoliation is mostly a temporary cosmetic inconvenience at the end of the season, and the trees almost always recover the following year. However, continued major defoliation of a particular tree might inhibit its growth or productivity.
One key to controlling them is to watch for them early, say in July or August. If a small tent appears, remove it. This approach, of course, will require perseverance for the first year or two, and the webworms have their own cycles as well, so regardless of preventative efforts, they might suddenly appear again in three or four years, anyway.
According to the Baxter County Cooperative Extension office, moths in mid-spring “lay clusters of up to 500 greenish eggs on leaf surfaces of host trees. The eggs are partly covered with white hairs or scales and usually occur on leaves near the ends of branches.” This would seem to be an opportunity for intervention by a careful observer.
The Baxter County article goes on to state the larvae are about an inch long when mature. At that point, “they crawl down the tree to spin a cocoon and pupate in the ground litter in July. There are two generations a year – the first in early June (into July) and the second and normally the largest and most damaging generation of larvae present in August and September (sometimes into early October). Larvae from the second generation remain in the pupal stage until the next spring, when the moths emerge to begin the cycle again.”
This pattern would seem to suggest two more chances to interrupt the cycle. One would be to watch for larvae as they migrate up and down the tree trunk. If the population in their tents is any indication, there would be hundreds of them, and what happens next would be up to the one watching. Also, cultivating under the tree should disturb their happy hibernation and expose them to predators.
Sources also suggest there are horribly terrible poisons an environmentally-insensitive homeowner could spray on them once the tents have been pierced or their off-season hideouts opened up. Then again, a safer choice would be Bacillus thuringiensis, sold as Thuricide, a natural pesticide proved to be effective in controlling caterpillars.
Apparently, some homeowners try to get rid of the webworms by burning the affected parts of the tree. Reliable sources are unanimous that this bonehead strategy would only damage the tree far worse than webworms ever could.
Bagworms
The real bagworms, Thiridopteryx ephemeraeformis, do not make web-like tents. An article from the University of Kentucky Department of Entomology states, “Bagworm caterpillars make distinctive 1.5 to 2-inch long spindle-shaped bags that can be seen hanging from twigs of a variety of trees and shrubs. Sometimes the bags are mistaken for pine cones or other plant structures.” A bagworm will begin in spring to envelop themselves with bits of plant material from its host as protection and camouflage while it feeds. These larvae can defoliate and kill a tree if abundant enough.
Bagworms have been considered a serious pest in Florida orange groves. In Arkansas, they are known to affect junipers, red cedars, Leyland cypress and arborvitae as well. However, in Madagascar, they are encouraged because the protein-rich pupae are collected as food. Yum!
Eastern tent caterpillars
The handiwork of the Eastern tent caterpillar bears a closer resemblance to fall webworm webs but with distinct differences. Tent caterpillars prefer fruit trees such as wild cherry, apple, peach, plum and others.
A cluster of Eastern tent caterpillar eggs encircle a host branch through the winter in a dark varnish-appearing mass with a texture like Styrofoam. They begin to hatch in early spring and gather at a crotch of the host to begin their tents.
Mature tent caterpillars are a bit larger than fall webworms, but they will have done their damage before fall webworms appear. Another difference is tent caterpillars wander from their host trees. The same University of Kentucky article mentions, “They [tent caterpillars] are frequently seen crawling on other types of plants, walkways and storage buildings. They are a nuisance and can create a mess when they are squashed on driveways, sidewalks and patios.”
The same prevention and treatments strategies apply for tent caterpillars and fall webworms.