A full grown silverfish or firebrat is about ¼-½ inch long. Both insects lack wings and have carrot-shaped bodies, thick at the front and tapering towards the posterior. The young look identical to the adults, but are smaller. Silverfish and firebrats have two long antennae on their heads and three tail-like appendages on the tips of their abdomens. The five appendages are approximately as long as the body. Silverfish have uniformly colored silver bodies while firebrats have mottled gray-brown colored bodies. Both insects can move very fast when disturbed and homeowners often mistake them for cockroaches.
Silverfish and firebrats can be accidentally brought into buildings with boxes of materials that have been stored in infested areas. They can also move indoors from the outside. Once inside structures, they move quickly through buildings in search for food. When they find a source, they will generally stay close to it.
Silverfish and firebrats are general feeders, consuming a large variety of materials. They especially eat foods and products that are high in protein, sugar, or starch. This includes vegetable foods, such as flour and cereal; fabrics, including cotton, linen, silk, and rayon; sizing in paper; starch in clothing; and paste or glue. They also eat wallpaper, book bindings, and paper when trying to feed on the glue or paste underneath them. Their damage is usually recognized from their irregular feeding marks and the presence of feces. Silverfish and firebrats can go for months without feeding.
Both insects are active at night and hide during the day. They lay eggs in cracks, crevices, and other narrow, confined spaces. Silverfish prefer cool, moist, dark places with temperatures between 70o - 80° F and a relative humidity between 75% - 95%. They are often associated with basements, closets, bookcases, and storage areas. Firebrats also prefer damp areas but in places with temperatures over 90° F. They are found in boiler and furnace rooms, steam tunnels, insulation around hot water or heating pipes, bakeries, and similar places. Both silverfish and firebrats can also be associated with leaking or unventilated roofs and can be found on upper floors in buildings (if sufficient humidity exits (i.e. bathrooms).
Silverfish and firebrats run with characteristic, quick movements, stopping at short intervals and then moving on rapidly. These insects can not climb on smooth vertical surfaces and may be found trapped in sinks, bathtubs, and similar places. Despite the circumstantial evidence, they do not come up out of drains.
Silverfish and firebrats are primarily nuisance insects, usually causing little damage. Although very uncommon, the potential exists for large, uncontrolled infestations of silverfish and firebrats to damage paper, book bindings, wallpaper, cereals, starched fabrics, leather, fur, silk and rayon. Silverfish and firebrats are not associated with the spread of any disease.