Silverfish

Lepisma saccharina (commonly called the fishmoth, urban silverfish or just the silverfish) is a small, wingless insect. Its common name derives from the animal's silvery grey colour, while the scientific name indicates the silverfish's diet of carbohydrates such as sugar or starches. It belongs to the basal insect order Thysanura, and the species is estimated to have existed for 300 million years.

An eyeless species of silverfish, or a close relative, was discovered in January 2006 in caves in Sequoia National Park, California.

Appearance The body of a silverfish is approximately 10 mm long, excluding the antennae and caudal furcae. The metallic sheen is due to silvery scales, which only appear after the third moult.

Development Silverfish require between four months and three years to grow from an egg to an adult. Silverfish may live up to eight years, and moult up to eight times. Under favourable conditions, silverfish may moult up to four times per year. At temperatures between 25 and 30 °C, females lay clutches of about one hundred eggs, usually in a crevice. If conditions are too cold or dry, silverfish cannot reproduce.

Diet The favourite food of silverfish is any matter that contains starch or polysaccharides, such as dextrin in adhesives. These include glue, book bindings, photos, sugar, hair, dandruff, and dirt. Silverfish can also cause damage to books, tapestries, and textiles. Apart from these cases, the damage caused by silverfish is negligible, and they have no direct effect on human health beyond psychological distress to people who dislike them. Other substances that may be eaten include cotton, linen, silk and synthetic fibres, and dead insects or even its own exuvia (moulted exoskeleton). During famine, a silverfish may even attack leatherware and synthetic fabrics. In extreme cases, silverfish may live for several months without feeding.

Habitat The silverfish is a widespread commensal in human dwellings, much like its relative, the firebrat (Thermobia domestica). Silverfish can often be found under refrigerators or around a well-heated toilet, if the crevices in the floor tiles are large enough. Firebrats prefer warmer conditions, and can be found in bakeries, where they feed on flour and bread, as well as other animal products.

Reproduction Due to their nocturnal nature, the reproduction of silverfish has only recently been studied. The male lays a spermatophore, a sperm capsule covered in gossamer. Having located the spermatophore via a variety of biochemical signals, the female finds the spermatophore and takes it up for fertilisation.

Predation Earwigs and house centipedes are known to be predatory upon silverfish.

Elimination In buildings, silverfish can only exist in sufficiently humid, crevice-rich environments. If these two conditions are removed, the silverfish will not be able to survive. Other measures that may be taken to eliminate silverfish, at least temporarily, include the following:

   A 1:1-ratio dispersion of borax and sugar is a reliable bait to kill silverfish.

   The scent of a sal ammoniac solution should drive away silverfish within 24 hours.

   To capture silverfish, sprinkle plaster on a wet, white cotton cloth, put it in a corner overnight, near the silverfish's hideout.

   Another useful way to capture silverfish is to put a grated potato on a slab by their hideout overnight. The silverfish will crawl into the potato to feed. The next morning, the whole potato, along with the silverfish inside, can be disposed of.


Further Reading:
Hadlington, P. and Marsden, C. (1999) Common Household Pests: A Homeowners Guide to Detection and Control, UNSW Press.

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