most mites are harmless in small numbers, and can even be beneficial. But if large numbers of mites are present they can stress your scorpion out. Especially if large amounts gather on the scorpions joints. Best thing to do would be to clean your Dubia tub. Check your scorpion over for signs of mites and if present change the substrate. If you keep having problems with mites you can order predatory mites that will kill the others.