Silverfish and Fire Brats: Thysanura

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Thysanurans (thigh-suh-NOOR-uhns) have no wings. Their flattened bodies typically are covered with overlapping silvery gray scales. Most species are 0.4 to 0.8 inches (10.2 to 20.3 millimeters) in length, but a few species range from 0.04 to 1.9 inches (1 to 48.3 millimeters). One fossil (FAH-suhl) thysanuran, about 350 million years old and measuring 2.36 inches (60 millimeters), is the largest silverfish known. The thysanuran head may or may not have small eyes, each eye with several lenses. The antennae (an-TEH-nee), or feelers, are long and threadlike. Like those of all insects, the mouthparts of thysanurans are on the outside of the head. Each jaw is attached to the head at two points.

Silverfish and fire brats have ten-segmented abdomens. All but the first abdominal segments have paired structures underneath to help support the abdomen and keep it from dragging on the ground. The tip of the abdomen has two shorter tails and one longer, threadlike tail. Thysanuran larvae (LAR-vee), or young, look like the adults.


Thysanurans are found worldwide.


Thysanurans are found in moist habitats, but a few are found in sandy deserts. They live under bark, rocks, rotting logs, and leaf litter. Some species prefer to live in caves, among ants or termites, or with people.


Thysanurans eat decaying or dried plants and animal remains. Species living with people feed on starchy materials, such as paper, cardboard, book bindings, wallpaper paste, and some fabrics. They also eat the starch used to make fabrics stiff. Species living with ants get food by stealing it from their hosts.


The flat bodies of thysanurans allow them access to all kinds of narrow spaces as they search for food and mates at night. During the day they hide under stones or leaves. When they are alarmed, they can move with incredible speed.

Although the females of some species of silverfish can reproduce without mating, most species require males and females to produce fertilized eggs. Males deposit a sperm packet on the ground, beneath a silken thread. The packet is later picked up by the female. Females lay their eggs inside cracks and between spaces in leaf litter. The eggs are about 0.04 inches (1 millimeter) long and are longer than they are wide. At first they are soft and white, but after several hours they turn yellow and then brown. The larvae resemble small adults. Silverfish continue to molt, or shed their outer skeletons, throughout their lives and may live for up to six years.


Some species of silverfish are especially suited for living with people. They have been accidentally transported throughout the world. These species are considered household pests because of the damage they cause to household goods as they feed.


Fire brats live mostly with humans and prefer homes and buildings where both the temperature and moisture levels are high. They often are found near hot-water pipes, heaters, and fireplaces as well as ovens in bakeries. Their eggs take only twelve to sixteen days to hatch at 98.6°F (37°C). At 104°F (40°C) fire brats grow quickly, shedding their external skeletons every nine to eleven days. They live for about two years and will molt forty-five to sixty times.


No species of thysanuran are threatened or endangered.


Physical characteristics: Adult silverfish measure up to 0.4 inches (10.2 millimeters) in length. Their bodies are covered with silvery scales.

Geographic range: Silverfish probably originally came from tropical Asia; the species is now found living with people worldwide.

Habitat: This species lives in warm, damp places in the home, especially basements, closets, bookcases, shelves, and baseboards.

Diet: Immature and adult silverfish are fond of flour and starch and are sometimes found in cereal; they also feed on muslin, starched collars and cuffs, lace, carpets, fur, and leather. They are also cannibalistic, feeding on molted silverfish skins and dead and injured individuals.

Behavior and reproduction: Silverfish forage, or search, for food at night. They spend their days hidden in dark, protected places.

The male spins a silk thread and deposits a packet of sperm underneath; the female picks it up and places it in her reproductive opening. Eggs are laid singly or in small batches of two to three and deposited in crevices (KREH-vuh-ses) or under objects. Under the best conditions, a female lays an average of one hundred eggs during her life span. The larvae have no scales up to the time of their third molt. After ten molts, they reach sexual maturity; the adults, with a life span of two to eight years, keep molting about four times every year.

Silverfish and people: Silverfish are considered household pests because their feeding activities damage household goods.

Conservation status: Silverfish are not threatened or endangered. ∎


Physical characteristics: The long, slender body of this thysanuran grows as long as 0.47 inches (12 millimeters), without antennae or tails. The antennae are one and half times the body length, and the tails are slightly longer than the body, growing to 1.41 inches (35.8 millimeters). These thysanurans do not have eyes, and their whitish or transparent, or see-through, bodies lack scales.

Geographic range: This species is only known from the Toca da Boa Vista caves in the north of Bahia, Brazil.

Habitat: They prefer the deepest and wettest areas of the cave, near standing bodies of water.

Diet: The species feeds on dry leaves and other plant tissues carried into the cave by bats. They also probably eat the paper wrapping of markers left years ago by scientists studying the caves.

Behavior and reproduction: Very little is known about the behavior of this species. They are usually found running quickly over rock formations on the cave floor. Males are unknown, which might mean that females can reproduce without mating.

Cubacubana spelaea and people: This species has no direct impact on humans or their activities.

Conservation status: This species is not threatened or endangered. ∎


Web sites:

"Critter Catalog: Silverfish." BioKids. (accessed on September 2, 2004).

"Thysanura: Silverfish and Firebrats." Tree of Life Web Project. (accessed on September 2, 2004).

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Silverfish and Fire Brats: Thysanura

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