Firebrats Thermobia domestica scatter as they are exposed to light. Firebrats belong to a primitive group of insects called the bristletails and are household pests that can damage books and fabrics, and contaminate food. The bristletail group gets its name from the bristle_like appendages, called filaments, found at the end of their abdomen and which are organs of touch. Adults can reach a length of 1.5 cm and are found in most parts the world.