Silverfish and Firebrats

Silverfish and Firebrats are small, primitive, wingless insects, fossils of which are found dating back to the Middle Devonian Period, roughly 395 million years ago. These interesting “living fossils” can sometimes be considered a nuisance in the home since they eat a wide variety of foods, including glue, wallpaper paste, paper, photographs, cotton, flour, cereals and leather.

Common types

Both Silverfish (Lepisma saccharina) and Firebrats (Thermobia domestica) are soft bodied and covered with fine scales that are silvery to brown in color. These insects belong to the order Thysanoptera, a name that is derived from the Greek words thysanos (fringe) and oura (tail).

Adults are up to 3/4 inch long, flattened from top to bottom, elongated and oval in shape, being broad near the head and tapering toward the rear making them appear “carrot” shaped. There are two long, slender antennae at the head and three long, antennae-like appendages at the rear, one of which is directed straight back and the other two curving outward. On account of this, these insects are sometimes known as “bristletails.”

These insects can also run very swiftly with a wiggling motion that resembles the swimming action of a fish. The firebrat is quite similar in habits but is generally darker in color with much longer antennae and tail and lacks the silvery sheen of silverfish.


While silverfish prefer damp cool places (with a humidity of 75 to 95 percent) and can be found throughout the home, the aptly named firebrat has a similar high humidity requirement but prefers temperatures over 90° F. As a result, the firebrat is usually found near furnaces, ovens, heating pipes, water heaters, fireplaces, and other heat sources. These insects normally first enter the home by being carried in on food, furniture, old books, papers and old clothing.

Both silverfish and firebrats are chewing insects and general feeders but prefer carbohydrates and protein, including flour, dried meat, oats, paper and glue. Silverfish and firebrats are active at night and hide during the day. When objects are moved where they are hiding, they dart out and seek new hiding places.

Sometimes they can be found trapped in a bathtub or washbasin, unable to climb out. Large numbers may be found in new buildings where the walls are still damp from plaster and fresh lumber. They are long-lived, surviving from two to eight years, and can survive a year without food. Silverfish and firebrats undergo only slight metamorphosis as they grow, the main external change being the appearance of scales after the first few months.

There are at least 6 nymphal stages or instars before developing into an adult. Unlike most other insects, they continue to molt after becoming adults, with over forty molts recorded for one firebrat. Populations of these insects do not build up fast, and a large number in a home usually indicates a longtime infestation. Silverfish females may lay over 100 eggs during a lifetime with eggs laid singly or two to three at a time in small groups, hatching in three to six weeks.

Firebrats by contrast lay about 50 eggs at one time in several batches. Firebrat eggs hatch in about two weeks under ideal conditions. Young silverfish and firebrats resemble adults except being smaller, white and take on the adult color in four to six weeks. Adults can live up to eight years. Silverfish and firebrats may reach maturity in from three to twenty-four months.

Health issues

Silverfish and firebrats are pests primarily because they consume or stain foods, fabric, paper, books, or wallpaper. Damage to these items is significant, however, only in cases where very large infestations build up over long periods of time.

Silverfish control


While good sanitation is important it is not entirely effective in reducing populations because these insects often reside between wall partitions, in books and papers and in other protected places. Removing old newspapers, books and fabrics as well as clearing away spilled food and minimizing the storage of food over long periods of time all help reduce this insect’s abundance. Lowering the home’s humidity with dehumidifiers and repairing leaking pipes to eliminate moisture sources may also be beneficial. Once an infestation has been eliminated, good sanitation can help prevent reinfestation.

Chemical Control

There are many homeowner insecticides labeled for control of silverfish and firebrats that can be applied as sprays, dusts, or baits if conditions merit. Before using any insecticide, always read the label and follow directions and safety precautions. Treat cracks, crevices, wall voids and other likely hiding spots in areas where these pests are noticed.

Control may not be immediate since insects need to move out and contact the insecticide deposit for these residual products to become effective. When infestations are persistent and hard to locate, it is advisable to use the services of a reputable, licensed pest control operator or applicator.