Silverfish are nocturnal, elongate, and flattened insects typically between 0.5 and 1.0 inches (12–25 mm) in length. Their abdomen tapers at the end, giving them a fish-like appearance. They are born whitish, but develop a grayish hue and metallic shine as they get older. They have three long cerci at the tips of their abdomens, one parallel to their body, one facing left, and one facing right. They also have two small compound eyes, despite other members ofThysanura being completely eyeless, such as the family Nicoletiidae.

Like other species in Apterygota, silverfish completely lack wings. They have long antennae, and move in a wiggling motion that resembles the movement of a fish. This, coupled with their appearance, influences their common name. Silverfish typically live for two to eight years.

Silverfish consume matter that contains polysaccharides, such as starches and dextrin in adhesives. These include glue, book bindings, paper, photos, sugar, coffee, hair, carpet, clothing and dandruff. Silverfish can also cause damage to tapestries. 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 leatherwear and synthetic fabrics. Silverfish can live for a year or more without eating.