Probably related to Gullyslugs. The D. scrabbles through ventilator shafts and pipes. It is not of any danger - except to rats, bugs and spiders of course. D. are believed to weigh nothing, since they never leave prints. I think, they might just be able to ignore gravity and are exceptional climbers. They're annoying, since they are the source of many funny sounds old and new buildings produce. Old D. creak while young once scrabble and screetch over metal.
How to fight it
No need to. If you have D. in your wall, it is a good sign, because they would fear anything more dangerous that might also hide in the walls.gab