Silverfish and Fire Brats: Thysanura

Thysanurans (thigh-suh-NOOR-uhns) have no wings. Their flattened bodies typically are covered with overlapping silvery gray scales. Most species are 0.4 to 0.8 inches (10.2 to 20.3 millimeters) in length, but a few species range from 0.04 to 1.9 inches (1 to 48.3 millimeters). One fossil (FAH-suhl) thysanuran, about 350 million years old and measuring 2.36 inches (60 millimeters), is the largest silverfish known. The thysanuran head may or may not have small eyes, each eye with several lenses. The antennae (an-TEH-nee), or feelers, are long and threadlike. Like those of all insects, the mouthparts of thysanurans are on the outside of the head. Each jaw is attached to the head at two points.

Silverfish and fire brats have ten-segmented abdomens. All but the first abdominal segments have paired structures underneath to help support the abdomen and keep it from dragging on the ground. The tip of the abdomen has two shorter tails and one longer, threadlike tail. Thysanuran larvae (LAR-vee), or young, look like the adults.