Silverfish

Silverfish are primitive, wingless insects that have remained virtually unchanged for over 400 million years — predating even dinosaurs. These teardrop-shaped, silver-scaled insects are 12-19mm long with three long tail-like appendages and two long antennae. They are nocturnal, extremely fast runners, and prefer dark, humid environments with relative humidity above 75%.

Silverfish feed on starches, sugars, and cellulose-based materials. Their diet includes book bindings, wallpaper paste, photographs, documents, cotton and linen fabrics, cereal, flour, and even the glue on postage stamps and cardboard boxes. They can also feed on dead insects, leather, and synthetic fabrics. This broad diet makes them a genuine threat to libraries, archives, stored clothing, and important documents.

A female silverfish lays 1-3 eggs per day in cracks and crevices, depositing roughly 100 eggs over her lifetime. Silverfish develop slowly — taking 3-4 months to reach adulthood — but they are exceptionally long-lived for an insect, surviving 3-8 years. This longevity means that even a small population sustains itself over years if conditions are favorable.

Silverfish thrive in bathrooms, basements, attics, kitchens, and laundry rooms — anywhere with consistent moisture. They are often found behind baseboards, in wall voids, under sinks, inside stored boxes, and between book pages. Because they are nocturnal and avoid light, infestations can grow unnoticed for months or years.

A closely related species, the firebrat (Thermobia domestica), prefers warmer environments (above 90 degrees F) and is commonly found near furnaces, ovens, and hot water heaters. Both species cause similar damage and are treated with the same methods.

Silverfish do not bite, sting, or transmit diseases, so their danger level is low from a health perspective. However, the property damage they cause — particularly to irreplaceable items like photographs, family documents, and book collections — can be significant over time.