A dirt demon is just a lump. Just like a dust bunny is just a clump of dust.
Have you ever heard of the game "Katamari Damacy?" That game is about a little guy who rolls a ball around, turning it into a bigger and bigger lump. What do you think the Katamari (かたまり) part means? It means lump, of course.
Currently there are no similar looking kanji which exist in the WaniKani learning system