A silverfish (Lepisma saccharina) is a small, wingless insect in the order Thysanura. Its common name derives from the animal's silvery light grey and blue color, combined with the fish-like appearance of its movements, while the scientific name (L. saccharina) indicates the silverfish's diet consists of carbohydrates such as sugar or starches.
Silverfish are nocturnal insects typically 13–25 mm (0.5–1.0 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 two long cerci and one terminal filament at the tips of their abdomens, the filament projects directly off of the end of their body, between the left and right cerci. 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 avoid light.
Silverfish are a cosmopolitan species, found in Africa, the Americas, Australia, Eurasia, and other parts of the Pacific. They inhabit moist areas, requiring a relative humidity between 75% and 95%. In urban areas, they can be found in attics, basements, bathtubs, sinks, kitchens, and showers.
Before silverfish reproduce they carry out a ritual involving three phases, which may last over half an hour. In the first phase, the male and female stand face to face, their quivering antennae touching, then repeatedly back off and return to this position. In the second phase the male runs away and the female chases him. In the third phase the male and female stand side by side and head-to-tail, with the male vibrating his tail against the female. Finally the male lays a spermatophore, a sperm capsule covered in gossamer, which the female takes into her body via her ovipositor to fertilize her eggs. The female lays groups of fewer than 60 eggs at once, deposited in small crevices. The eggs are oval-shaped, whitish, about 0.8 millimetres (0.031 in) long, and take between two weeks and two months to hatch. A silverfish usually lays fewer than 100 eggs in her lifetime.
When the nymphs hatch, they are whitish in colour, and look like smaller adults. As they moult, young silverfish develop a greyish appearance and a metallic shine, eventually becoming adults after three months to three years. They may go through 17 to 66 moults in their lifetime, sometimes 30 in a single year - much more than most insects. Silverfish are among the few types of insect that continue to moult after reaching adulthood.
Silverfish consume matter that contains polysaccharides, such as starches and dextrin in adhesives. These include book bindings, carpet, clothing, coffee, dandruff, glue, hair, some paints, paper, photos, plaster, and sugar. They will damage wallpaper in order to consume the paste. Silverfish can also cause damage to tapestries. Other substances they may eat include cotton, dead insects, linen, silk, or even their own exuvia (moulted exoskeleton). During famine, a silverfish may even attack leatherware and synthetic fabrics. Silverfish can live for a year or more without eating if water is available.
Silverfish are considered household pests, due to their consumption and destruction of property. However, although they are responsible for the contamination of food and other types of damage, they do not transmit disease. Earwigs, house centipedes, and spiders are known to be predators of silverfish. Silverfish die on contact with toxins such as Permethrin or Deltamethrin.
The scientific name for the species is Lepisma saccharina, due to its tendency to eat starchy foods high in carbohydrates and protein, such as dextrin. However, the insect's more common name comes from the insect's distinctive metallic appearance and fish-like shape. While the scientific name can be traced back to 1758, the common name has been in use since at least 1855.
Together with jumping bristletails, the predecessors of silverfish are considered the earliest, most primitive insects. They evolved at the latest in mid-Devonian and possibly as early as late Silurian more than 400 million years ago. Some fossilized arthropod trackways from the Paleozoic Era, known as Stiaria intermedia and often attributed to jumping bristle may have been produced by silverfish.
Other similar insect species are known as silverfish. Two other silverfish are common in North America, Ctenolepisma longicaudata and Ctenolepisma quadriseriata. Ctenolepisma urbana is known as the urban silverfish. The Australian species most commonly referred to as silverfish is a different lepismatid, Acrotelsella devriesiana. The firebrat (Thermobia domestica) is like a silverfish but smaller and with darker markings of brown and black.