Why Are Woodpeckers Called "The Doctors of the Forest"?

Flying back and forth in the forest, woodpeckers stop at this tree at one moment and that tree the next. A woodpecker holds the tree trunk tightly with its claws, props itself up with its tail and knocks at the tree trunk with its beak to see whether there are any worms inside the trunk. if the knock doesn't sound right, a wood-pecker will peck a hole into the tree with its long beak, stretch the tip into the hole, dig out the won-n with its thin, long, hooked tongue, and eat it. in this way, woodpeckers patrol and knock in the forest day by day, eating injurious worms inside trees. So, woodpeckers are called "the doctors of the forest."