Silverfish have elongated, flattened bodies that are usually covered with scales. They lack wings and have long antennae with many segments. At the abdomen tip are 3 appendages that look like antennae or “tails,” and the eyes are small, compound, and on opposite sides of the head. They run quickly on their six legs.
The common silverfish (Lepisma saccharina) is silvery, tapered toward the tail, about ½ inch long, and lacks stripes, bars, or other markings. The firebrat (Thermobia domestica) is shorter and stouter, not as tapered at the abdomen tip, is more yellowish, with brown bands and spots above.
Similar species: Bristletails (in the order Microcoryphia) are cylindrical (not flattened), with an arched or humped thorax, usually darker and mottled, with large eyes that touch (not on opposite sides of the head). They live outdoors under bark or stones or in leaf litter (never in houses) and move by jumping.