The silverfish (Lepisma saccharina) is a small, wingless insect known for its metallic, silvery appearance and quick, wiggling movement. These creatures are considered one of the most ancient insects on Earth, having survived largely unchanged for millions of years. Homeowners rarely see them because they are strictly nocturnal pests, reserving their active foraging and movement almost entirely for the hours of darkness. This hidden behavior allows them to avoid detection while they search for starches and cellulose materials.
Why Silverfish Are Active at Night
Silverfish are nocturnal primarily as a survival mechanism driven by photophobia, an intense aversion to light. Their highly sensitive compound eyes cause them to retreat instantly when exposed to illumination. This desire for darkness shields them from daytime predators like spiders and centipedes, as their only defense is speed.
The nighttime hours also provide the specific environmental conditions necessary for their survival, particularly moisture. Silverfish are vulnerable to desiccation and require a relative humidity between 70 and 90 percent to thrive. As temperatures drop at night, the relative humidity often increases, creating an optimal foraging window for them to leave their shelters. They emerge to seek food and water, though they can survive for weeks without a meal if humidity levels are sufficient.
Hiding Spots During the Day
During the day, silverfish retreat to tight, undisturbed spaces that offer darkness, moisture, and proximity to starchy food sources. They are commonly found in high-humidity areas of the home, such as bathrooms, basements, and attics. These insects exploit small entry points, often hiding in wall voids, under subflooring, and behind baseboards.
Silverfish seek out specific micro-habitats for shelter and sustenance. They frequently hide in the bindings of books, stacks of old papers, and inside cardboard storage boxes, as these items serve as both food and shelter. Homeowners may also find them under sinks, near plumbing fixtures, or behind loose wallpaper, where they feed on starch-based glues. Their preference for undisturbed, dark crevices means that items stored long-term in garages or sheds are also prime daytime hiding spots.
Identifying Signs of Infestation
Because silverfish operate exclusively at night, the most reliable way to confirm their presence is by identifying the physical evidence they leave behind.
One indicator of an infestation is the presence of their feces, which appear as tiny, dark brown or black specks resembling ground pepper. These droppings are typically found scattered where the insects have been feeding or resting.
Silverfish also shed their skin numerous times, leaving behind translucent, scale-like exoskeletons. These shed skins are often found near their harborages. The most noticeable sign is the feeding damage they inflict on household items containing starches or cellulose. This damage appears as irregular holes, notches along the edges, or surface etchings on paper, fabric, wallpaper, and book bindings, sometimes accompanied by a yellowish stain.