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Previously called Thysanura

Pronunciation:  [Zy⋅gen⋅TOE⋅ma]

Common Name:  Silverfish / Firebrats

Greek Origins of Name:  The name Zygentoma is derived from the Greek ζυγον, (zygon meaning “yoke” or “bridge”), and εντομα (entoma meaning “cut into”).  The idea behind the name was that the taxon represented an evolutionary link (hence “yoke or bridge”) between the Pterygota and the Apterygota (the two suborders within “entom” ology).   This view is now totally obsolete, but the name became firmly established in the late 19th and early 20th century — well before modern phylogenomic methods were developed.

Spot ID Key Characters:

  1. Apterygote (primitively wingless)
  2. Three terminal filaments, roughly equal in length
    including two cerci and a median caudal filament
  3. Eyes small or missing
  4. Body flat, often covered with dusty scales


Ametabolous development, i.e. lacking metamorphosis;  eggs hatch into young which are smaller than adults, but similar in appearance.


Apterygota, primitively wingless


Common in domestic and sylvan habitats worldwide.  Approximately 3 families and 18 species in North America and 5 families and ~370 species worldwide

Life History and Ecology:

Silverfish are fast-running insects that hide under stones or leaves during the day and emerge after dark to search for food.   A few species are resistant to desiccation and well-adapted to survive in domestic environments such as basements and attics.   Silverfish are scavengers or browsers; they survive on a wide range of food, but seem to prefer a diet of algae, lichens, or starchy vegetable matter.

Zygentomans may be rather long-lived — three years is probably typical and up to seven or eight years may be possible.   They continue to molt frequently, even after reaching adulthood.

Silverfish have an elaborate courtship ritual to insure exchange of sperm.   The male spins a silken thread between the substrate and a vertical object.   He deposits a sperm packet (spermatophore) beneath this thread and then coaxes a female to walk under the thread.   When her cerci contact the silk thread, she picks up the spermatophore with her genital opening.   Sperm are released into her reproductive system, and then she ejects the empty spermatophore and eats it.

Appearance of Immatures and Adults:

  1. Body relatively flat, tapered and often covered with scales
  2. Compound eyes small or absent
  3. Antennae long, thread-like, and multisegmented
  4. Abdomen with ten complete segments
  5. Eleventh abdominal segment elongated to form a median caudal filament
  6. Cerci present, nearly as long as median caudal filament
  7. Styliform appendages located on abdominal segments 7-9

Economic Importance:

Domestic species such as silverfish and firebrats may cause extensive damage to household goods.   They often feed on wallpaper paste, bookbindings, and the starch sizing of some textiles.   Cardboard and other paper products may also be damaged.

Major Families:

Lepismatidae — Most of the North American species belong to this family, including the silverfish (Lepisma saccharina) and the firebrat (Thermobia domestica).

Fun Facts:

  • Firebrats have been known to live more than 6 years — through 60 instars.  It has been suggested that frequent molting is an adaptation that reduced the risk of infection by parasitic fungi.
  • One family of Zygentoma (Nicoletiidae) is adapted to live underground in caves, mammal burrows, or in the nests of ants or termites.  Some species mimic ants and steal their food.
  • For many years, the family Lepidotrichidae was known only from Oligocene fossils.  It was thought to have been extinct until 1959 when living specimens were discovered in northwestern California.

Picture Gallery: