Silverfish (Lepisma saccharina) are not fish at all but rather small, primitive, silvery light grey and blue wingless insects in the order Thysanura.
Nocturnal, silverfish are typically half an inch to an inch long, have two long cerci and one terminal filament at the tips of their abdomens, and have two small compound eyes and long antennae, and move in a wiggling motion that resembles the movement of a fish. Living for two to eight years, silverfish are agile runners and can outrun most of their predators on horizontal surfaces, but, lacking additional appendages, are not fast enough to climb walls at the same speed.
They avoid light and inhabit moist areas, and can be found in attics, basements, bathtubs, sinks, kitchens, and showers.
Silverfish engage in a mating ritual involving the male and female standing face to face, touching their quivering antennae, followed by the male running away, to be chased and caught by the female, at which point the bugs stand side by side and head-to-tail, with the male vibrating his tail against the female, before laying 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 oval-shaped, whitish, 0.031-inch long eggs at once, deposited in small crevices.
After hatching, the nymphs moult, shedding their exoskeleton, and continue to do so into adulthood, perhaps as many as 60 times in their lifetime.
Silverfish consume matter that contains polysaccharides, such as starches and dextrin in adhesives, book bindings, carpet, wallpaper, clothing, coffee, dandruff, glue, hair, some paints, paper, photos, plaster, cotton, dead insects, linen, silk and sugar. They can live for a year or more without eating if water is available. Considered household pests due to their consumption and destruction of property and the contamination of food, they are not recognized as transmitting disease. Earwigs, house centipedes, and spiders are known to be silverfish predators.