When you see bagworms, they are usually in their larval form, hanging from a tree in a little bag they’ve spun together out of plant detritus – thus the name bagworms. They poke their little heads out and devour the tree’s leaves. Adult bagworms are moths – the males have a black, fuzzy body and clear wings, and the females look like worms. They have no wings or legs or antennae, and they live in the bags with the larvae.
Bagworms are found in most states east of the Rocky Mountains but are most prevalent in the Midwest and south from Texas to Florida. There are only about 600 species (a relatively small number in the insect world) and their bags can measure from 1 cm to 15 cm (almost 6 inches) in some tropical species.
Birds often eat bagworm bags that have eggs in them. The eggs have hard shells and can survive the birds’ digestive systems, thereby getting deposited elsewhere and promoting the spread of the bagworms over a large area.
Bagworms have just one generation per year, but not all the eggs hatch at the same time, so it may appear that there are several generations.
Some types of bagworms are monophagous (eating only one type of plant) and some are polyphagous (eating a variety of plants.) We usually see the common bagworm, Thyridopteryx ephemeraeformis, which feeds on arborvitae, eastern red cedars, and other junipers. However, depending on how heavy an infestation we’re having, they can feed on numerous other trees – spruce, pines, maples, black locust, oaks, sycamores, bald cypress, willows and even roses.
Bagworms can defoliate a tree, which can kill it, especially smaller trees. Deciduous trees like maples and sycamores can grow new leaves so they usually survive, but they’re weakened and will be more susceptible to borers (which can definitely kill a tree) or diseases.
Early detection is the best control. If you have trees that are susceptible, inspect them in the fall, winter, or early spring for bagworms. Any “bags” you find will usually contain eggs that will hatch in the spring. Picking them off and burning them will help cut down on infestations. (You must destroy the bags – if you put them in the trash, they will still hatch somewhere!) You can also check during late April or early May, when they hatch and start feeding. Again, pick them and burn them. Of course, if the affected tree is large, and you can’t reach them, this isn’t an option.
If spraying is necessary, bear in mind that small bagworms are a lot easier to kill than large ones! Susceptible trees should be sprayed at least by early June, and then at intervals to catch those larvae that hatched later.
If you would like to consider our tree and shrub program to control bagworms and other insects and diseases, and to keep your landscape healthy, we’d be happy to provide a free estimate. If you’re already a lawn customer and just need a one-time spray, just email us and we’ll get you a price!