The best way to remove bag worms from pine trees is to remove the bags by hand or to kill the bag worms using an insecticide. Controlling bag worm population is important as they can spread from tree to tree.
The bags of bag worms can be removed from the tree by hand, sealed in a plastic bag and thrown away. This is best done before hatching begins in late May. After eggs hatch, the bag worms can be killed by spraying the tree with an insecticide aimed at lepidopteran insects. After late May or early June, destroying the bag does not kill all the bag worms since the worms are mobile and not fully contained to the bag. Bag worms on pine trees are camouflaged as small pine cones.
After spraying the tree with pesticide, locate any remaining sacks, and remove them from the tree manually. The sacks can be placed in a bucket of soapy water to ensure the live worms in the sack are eliminated.
To determine the best way to deal with bag worms, understand their life cycle. Bag worms overwinter in their bags. When the larvae begin to hatch from May to early June, they eat the foliage of the pine tree. In August, the bag worms begin to build their bags for mating and laying eggs. The bags suffocate the tree and cause the areas they cover to brown and die.
Bag worms are actually caterpillars that grow to be an inch in length. They are a dull grey with darker markings close to their heads. Bag worm males eventually mature into small, black, fur-covered moths with clear wings, but the females remain in a larvae-like state and do not come out of the bag.