Do you have a bagworm infection in your trees? The bags they inhabit are easy to spot but often confused for cones or seed-bearing structures.

According to the University of Illinois Extension of Kankakee County and The Morton Arboretum, they take up homestead in conifer, arborvitae, spruce, eastern red cedar, other junipers or white pine trees.

The bags are usually 1.5- to 2-inches long and will look different depending on the host plant, the Morton Arboretum says. For example, the bag on a maple will look different from a bag on an arborvitae. Because bagworms add plant materials to the top of the bag, the freshest and greenest material is on the top of the bag. Inside the “bag” is, or was, a worm. A few of them and your trees would be OK, but a whole lot of them could eat down your tree or bush.

The dark brown bagworm caterpillars are 1/8- to 1/4-inch long when they first hatch, eventually reaching 1-inch long. As the insect feeds, it creates a silken case covered with the leaves made from the host plant, binding the bag together and attaching it to the plant with a silken thread.

Once a plant is infested, populations can grow quickly.

Life cycle

Bagworm young hatch in the overwintering bag and emerge in June to begin feeding, the extension says. They are blown to other plants easily. As they feed, female worms construct their case (bag) for about three months; sometimes during this stage, it is possible to see the bags “moving” as the worms move. In late summer the mature worms pupate for seven to 10 days; winged males emerge and exit the bag, and wingless females stay and mate while still in the bag. One female lays up to 1,000 eggs in the bag, where they will stay until the next year. Meanwhile, the female dies.

You will find bagworms feeding during the summer, but they are much easier to kill when they are small. These caterpillars remain susceptible to chemical treatment into early July. Heavy infestations can be unsightly with all the eaten foliage and can kill branches or whole plants.

By the time August comes, when bagworms are most likely to be noticed, these caterpillars already have formed their bags, it is too late for chemical control. Hand picking is an option.

So, now is the time to get outside and remove the bags. They can be handpicked and destroyed from fall through spring, thus removing the eggs and helping to eliminate the threat next year.

Damage being done

Bagworms usually begin feeding at the top of the tree, according to the extension office. When small, the worms feed in the layers of the leaf tissue, creating light patches on leaves. As they age, they consume entire needles or leaves.

A severe infestation could defoliate plants, which can kill branches or entire plants. A healthy deciduous tree or shrub that has been defoliated usually produces a new flush of leaves and survives. However, a defoliated evergreen cannot push out an additional set of leaves and might die.

Sources: University of Illinois Extension of Kankakee County and The Morton Arboretum

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