Bagworms, Webworms, or What?
Confusion sometimes surrounds the various insects which use silk to build shelters for themselves. I thought a short discussion about the ones we commonly see in Ohio might help clarify things a little. So, here goes....
 |
| Bagworm on red maple |
|
| Bagworm on juniper. Click on image for a larger view. |
 |
| From left: Eastern tent caterpillar, forest tent caterpillar, and gypsy moth larva |
 |
| Fall webworm larvae |
|
 Additional Information |
|
|
|
Bagworms (Thyridopteryx ephemeraeformis) can be serious pests, especially in landscapes. Beginning in late May through mid-June, larvae of this native moth feed on arborvitae, junipers, pines, spruces, and many deciduous trees. Larvae build loose silken bags which cover their entire bodies. Bags are camouflaged with pieces of plant material, and may be mistaken for natural parts of the tree. Females do not look like moths (no wings, legs, antennae, eyes, or mouthparts) and remain in silken bags throughout their entire lives. When larvae are fully grown, their protective bag is 1.0 to 1.5 inch long. In late summer, male moths (black, with nearly clear wings approximately 1 inch across), emerge from their bags after pupation. One generation occurs per year.
Eastern tent caterpillars (Malacosoma americanum) can cause significant defoliation during periodic outbreaks. This native insect favors cherry, apple, and crabapple trees, but will also attack ash, birch, blackgum, willow, witch-hazel, maple, oak, poplar, peach, and plum. Larvae build silken tents in the crotches of host trees in the spring. Caterpillars leave the nest to feed on newly opened leaves and as the caterpillars grow, so does the nest. Caterpillars are generally black, with a white stripe down the back. Yellow stripes and blue spots are found along the sides. Reddish brown adult moths emerge from white cocoons in late June or early July. One generation occurs per year.
Forest tent caterpillar (Malscosoma disstria) is another important native defoliator of eastern hardwood forests. In early spring, larvae begin feeding on aspen, blackgum, sweetgum, oak, birch, ash, maple, elm, and basswood. The larvae do not form a communal tent, rather individuals build small silken mats on the trunks of host trees which they use for resting cover. Caterpillars have whitish keyhole-shaped markings down the middle of their backs. Adults are small tan moths a little over 1.5 inches long. One generation occurs per year.
The gypsy moth (Lymantria dispar) is a serious exotic (non-native, introduced) pest of hardwood forests. Outbreaks can be severe, since natural enemy populations are often poorly developed. Small, black, hairy larvae hatch from egg masses in April and May and begin feeding on a wide variety of host trees. Preferred hosts, however, include oaks, apple, alder, basswood, hawthorn, aspen, and willow. Caterpillars do not build a nest or web. As they mature, they often feed at night and move down the tree to take refuge in shady places during daylight hours. Feeding stops around late July, larvae pupate, adults emerge and lay eggs in August. Mature larvae are hairy and have five pairs of blue spots and six pairs of red spots down the middle of their backs. Adult females are flightless, about 2 inches across, and whitish. Male moths are strong fliers, smaller, and dark brown with feather-like antennae. One generation occurs per year.
Fall webworm (Hyphanria cunea) is a less important native defoliator of hardwood forests because most of the foliar damage is done in the late summer and early fall after trees have produced and stored most of their energy away for the season. Fall webworm will feed on almost any deciduous tree, but prefers black walnut, hickory, cherry, and American elm. A larval colony will build a silken nest around foliage and begin feeding inside the nest. Larvae expand their nest to include new branches as they seek additional foliage on which to feed. Larvae are yellowish, hairy, and have either a black or red head. Two generations per year are common in Ohio.
As you can see, similarities in appearance among some of the insects described above may lead to misidentifying a problem in the forest. The use of terms like bag, web, and tent often add to the confusion when describing what you are seeing to others. I have attempted to point out the many differences among these insects, which should make them much easier to tell apart. When trying to decide which insect or damage you are looking at, consider all the factors you can. Look, of course, at the identifying features on any larvae or adults you can find. Also look at the species of the host tree(s), the time of year, and the type and location of any protective structures (nests, webs, etc.). Consideration of these factors may yield an answer through the process of elimination! |