The Worm People are worm-like beings with bulbous heads and green stripes. They range in size from normal worm size to significantly larger than Finn. Some are shown to speak English, as shown in "The Real You." It is possible that the ones that appear in that episode may be a different type of Worm from the ones shown in "Evicted!" and "King Worm."
The worms shown in "Evicted!" all seemed to be able to radiate waves from their heads, including the King Worm. When they do this, they bend their heads upward and make a "wawa" sound. They appear to do this when threatened. The smaller worms seem to have no effect on larger beings when doing this, but King Worm's waves may affect others.