Lepisma saccharina, commonly known as a silverfish or fishmoth, is a small, wingless insect in the order Thysanura. Its common name derives from the animal’s silvery light grey and blue colour, combined with the fish-like appearance of its movements, while the scientific name (L. saccharina) indicates the silverfish’s diet of carbohydrates such as sugar or starches.
Silverfish are nocturnal insects typically 13–30 mm (0.5–1 in) long. Their abdomens taper at the end, giving them a fish-like appearance. The newly hatched are whitish, but develop a greyish hue and metallic shine as they get older. They have three long cerci at the tips of their abdomens, one off the end of their body, one facing left, and one facing right. They also have two small compound eyes, despite other members of Thysanura being completely eyeless, such as the family Nicoletiidae.
Like other species in Apterygota, silverfish are completely wingless. They have long antennae, and move in a wiggling motion that resembles the movement of a fish. This, coupled with their appearance and silvery scales, influences their common name. Silverfish typically live for two to eight years. Silverfish are agile runners and can outrun most of their predators (including wandering spiders and centipedes). However such running is only possible on horizontal surfaces, as they lack any additional appendages and, therefore, are not fast enough to climb walls at the same speed. They also fear light.
Photo by Christian Fischer [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons