You may have had bagworm issues last year and called the local pest control to spray your yard and they used a pesticide that is non-specific and kills everything, bad as well as good insects. Additionally, you were probably not told that once you started seeing the new bags the worms were pretty much safe. There is a better way that is more environmentally friendly that targets only the bagworms and mid-winter is a good time to start preparing to determine when the worms are most vulnerable.
Bagworms can be treated effectively if you catch them in the right life stage. Worms hatch out in the early spring and begin feeding shortly thereafter. As they feed, they begin gathering materials to build their protective bag. A female worm never leaves her bag, lays eggs in her bag, dies, and the eggs over-winter, protected by the bag. When the weather becomes favorable in spring the eggs hatch and begin the next cycle.
Go out into your yard now and pick about 15 bags off your trees and shrubs and put them in a sealed plastic bag or jar. The bags that you will find are either abandoned male bags or female bags that contain eggs. Place the bags where they are exposed to outside temperature, out of the light, and watch the bag. When you start seeing tiny worms moving about in the bag, it is time to treat for them. It is important to treat while the worms are tiny and actively feeding before they can build their bags.
The most effective and environmentally friendly treatment is a spray of Bacillus thuringiensis or BT. This is a naturally occurring bacteria that makes toxins that affect immature insects (larva/caterpillars) when they eat it. The bagless larva will eat foliage that has been sprayed with the BT solution and get very ill. BT does not affect a wide range of insects like most chemical pesticides and the bacteria are only active for a few days after they are sprayed on your trees and shrubs. The bagworms have only one cycle a year, so at worst case you will have a lot fewer worms this summer.
Last year BT sold out quickly because it is an effective treatment for bagworms, army worms, and tent caterpillars but currently stores have it on their shelves. You might want to purchase a couple of bottles while there is plenty available.
Resources
https://agrilifeextension.tamu.edu/library/gardening/bagworms/
by Rob Franks, ECMG