A silverfish is featured on the left and a firebrat on the right.
Silverfish and firebrats belong to a group of primitive insects called thysanura. They are wingless and have slender, carrot-shaped bodies that are covered with scales. Both insects have two long slender antennae attached to their heads and three long tail-like appendages at the hind end. Each appendage is almost as long as the body. Adults are about 1/3 to 1/2 inch long (8 to 13 mm). Silverfish are shiny and silver or pearl-gray. Firebrats are mottled gray or brown.