Now that Japanese Beetles are on the way out, Bagworms are already in! A Bagworm is just as it sounds; a worm inside a bag. The newly hatched caterpillar starts out small but goes out with a bang. Mature larvae can reach from 1 to 2 inches inside their bags. Once fully enclosed inside the bag, they can have up to 1000 eggs to devastate the tree for the next year.