Silverfish 30-III
Archaeognatha & Zygentoma
A Silver fish on a wall.

Chapter Outline
  1. Description of Insecta
  2. Classification of Insecta
  3. Archaeognatha & Zygentoma
  4. Pterygota
  5. Neoptera
  6. Orthopteroidea
  7. Orthoptera
  8. Paraneoptera
  9. Endopterygota
  10. Diptera
  11. Hymenoptera
  12. Lepidoptera and Trichoptera
  13. Coleoptera


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Bristletails and Silverfish used to be lumped together in the same order. At a glance, the two types of organisms look quite similar. Insects in both orders have elongated bodies that taper towards the back, long antennae, three cerci (or "tails"), are wingless and are active at night. But there are enough differences upon further examination to warrant a separate classification in the view of some entomologists.

The main difference, which puts Archaeognatha in a group separate from all other insects, is the way in which the jaw attaches to the head. In Archaeognatha, the jaw attaches to the head by a single condyle, or joint. This is in comparison to the two condyles that connect the jaw to the head in all other insects. Because of this, insects are divided into two broad groups called "Monocondylia" and "Dicondylia". Archaeognatha is the only order of Monocondylians.

Unlike many insects, neither Bristletails nor Silverfishes go through metamorphosis. When their eggs hatch, the young look essentially like adults, only smaller. This is compared to a butterfly example where the young are caterpillars which go through metamorphosis to become butterflies.

There are more obvious ways to distinguish Bristletails from Silverfishes. Bristletails have large compound eyes, usually touching in the middle of the "face". Silverfishes have small compound eyes or none at all. Bristletails and Silverfishes both have three cerci, or "tails", but the middle one is much longer than the other two on Bristletails while all three cerci are about the same length on Silverfishes. Silverfishes can be seen running around quite fast but Bristletails are more likely to jump (up to 10cm) by quickly flexing their abdomens. And while both groups of insects can be found under bark, stones and leaf litter outside, only Silverfishes have added human homes to their habitat preferences.


The order of bristletails contains two families. The name Archaeognatha means "primitive jaw", which refers to the fact that bristletails have jaws that connect to the head by a single joint or condyle, which is considered more primitive than the type of jaws found on other insects. Bristletails can be found under bark, stones and leaf litter in grassy and wooded areas. They feed on algae, lichens and decaying plants. Their eyes will glow at night when a light is shined on them. Their ecological role is that of a decomposer, recycling nutrients locked up in dead organisms.



The order Zygentoma contains the silverfish and firebrats. Members of this order have three cerci (or "tails"). While similar to Bristletails, Zygentomans have some differences (see top of page).

Silverfishes, unlike bristletails, have taken to man-made environments such as homes. They can be seen scurrying across walls and trying to get out of bathtubs. While they prefer a diet of algae, lichens and decaying plants, they will also eat wallpaper glue, book bindings, cereal, cotton and other household items. In addition to man-made habitats, Silverfishes can be found under tree bark, rocks and leaf litter in wooded areas.

    • Forest Silverfish
    • Subterranean Silverfish

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