Silverfish are nocturnal insects typically 13–30 mm long.Their abdomens taper at the end, giving them a fish-like appearance.The newly hatched young 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.
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 the light.
Silverfish are 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 Roof voids, basements, bathtubs, sinks, and showers.
The reproduction of silverfish is preceded by 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 trembling 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 fertilise the eggs.