If someone were to conduct a bagworm census, I suspect they would find that populations have increased in northeast Kansas in the last few years. There are plenty of junipers and arborvitae to go around, and there are only so many ichneumon wasps (natural predators of bagworms).
Insect populations are often cyclical, and until either the predator population increases enough to decrease the bagworm population or food supplies become insufficient, we may continue to see more bagworms.
You might even have some of the ornament-shaped bags hanging from your trees and shrubs. If you did not pick them off already this year, as many as 1,000 babies can hatch from each bag, and they typically do so in northeast Kansas from mid-May to mid-June.
To control bagworms, either wait until they form new bags and pick them off later this summer, or begin control in the next few weeks. Baby bagworms are about 1/25 of an inch long, so look at your plants very closely over the next few weeks to confirm that the insects are present. The worms will soon begin to spin characteristic silken bags around themselves to protect their soft bodies.
If picking bagworms requires stilts or a ladder, you may wish to try an insecticide. There are both organic and conventional insecticides labeled to control bagworms, but read the label very closely on any product that you buy. Make sure the label says the product will control bagworms and that it is safe to use on the plant in question. With any product, thorough coverage of the tree or shrub is essential, and more than one application may be necessary.
Insecticides applied after mid- to late July are a waste of time and money. The tough silken bags protect the worms inside, and the insects typically stop feeding at this point in the summer.
Even though bagworms can cause substantial damage to evergreens (especially with repeat infestations), they are notable little creatures. Here are some interesting facts:
Baby bagworms “sail” on the wind. Before they begin spinning bags around themselves, bagworm larvae produce a long silken thread that catches the wind. Some bagworm babies will stay where they are to feed, while others float the breeze to another host. Infestations are often heavier on the south and west sides of landscape plantings because of prevailing winds.
Male bagworms transform into a clear-winged moth that looks a little like a moth, but female bagworms simply remain inside their bags and do not develop wings or legs. Male bagworms emerge in August, fly to female bags and mate before dying. Females produce eggs within the bags before dying. The eggs then overwinter inside the female bags before hatching the following spring.