Silverfish are small insects, usually between a half inch to an inch in length. Their name derives partly from their coloration, as they are a metallic grey or silver. The second half of their name comes from their body shape, as they are thicker in the front, around the head, and then taper off, similar to a fish. This also leads to fish-like movement when the run. They have long antennae, and do not have wings.
They are nocturnal, and will hide if exposed to light. Also, they are very fast runners, and can avoid most of their natural predators on a horizontal surface. They prefer areas of high humidity, and will often take up residence in bathrooms, kitchens, and damp basements. If undisturbed, silverfish can have relatively long lifespans, ranging anywhere from two to eight years.
Even with these longer lifespans, female silverfish typically lay less than 100 eggs through the course of their life. When eggs are laid they are in batches of less than 60 and hidden away in crevices. Hatching of the eggs can take anywhere from two weeks to two months depending on external conditions. Upon hatching, the baby silverfish, called nymphs, look like small versions of the adults but are white in color instead of the characteristic silver. They become darker and more metallic in color as they age, and they continue to molt and grow in size throughout their life.