Thysanurans undergo ametabolous metamorphosis, passing through egg, young and adult stages. Each new immature stage resembles the previous one in body form, only that it is larger. It is interesting that Thysanurans are one of the few insect orders in which moulting continues after the adult stage is reached. Thysanurans are silver-gray or brown in colour, and their bodies are usually covered in scales. Adults range in size from 1 to 50 mm in length. Some bristletails are found outdoors, under rocks and other objects in warmer parts of the world, but the common silverfish, and firebrats, (Thermobia domestica), normally inhabit houses and other buildings where they feed mainly on starchy products. Most species have three hair-like structures protruding from their abdomen, a median caudal filament and lateral cerci.