Size: About ¼ to ½ inch long, with a “carrot-shaped” body that’s thicker near the head and grows thinner toward the posterior.
Color: Dark grey or silver, with metallic-looking or shining scales
Silverfish are also sometimes called “bristletails”, because of the three distinctive, tail-like “caudal” (from Latin, meaning ‘tail’) appendages they have on the rear of their abdomens. The two “bristles” that point sideways to the left and right of the silverfishes’ abdomen are called “cerci”, while the one that points straight backward is called a “filament”. Both the cerci and the filament range in length and may be as long as the silverfishes’ body.
As arthropodal insects, silverfish have clearly segmented bodies that appear to taper off as the silverfishes’ body becomes more slender from head to abdomen.
Silverfishes’ bodies are covered in small, silvery scales. These scales detach from the silverfishes’ body very easily, which makes silverfish surprisingly difficult for predators to grab onto. These scales give silverfish their distinctive metallic or shiny appearance.
In addition to their abdominal cerci and filament, silverfish have two long, slender antennae or “feelers” extending outward from their heads. Silverfish use highly-developed sense receptors in these antennae as their primary means of navigating environments. A silverfishes’ antennae can sense the size and shape of objects in space, minute changes in air temperature and current, and more.
The second half of the scientific name for silverfish, saccharina, is derived from the Latin “Saccharum”, meaning sugar. Silverfish earned this name for their appetite for carbohydrates including sugars and starches.
Given their choice, silverfish prefer food high in protein, sugar, starch, or carbohydrates. They love to infest vegetables and vegetable bi-products, flour, cereal, various dried foods, dead insects, beef, and a wide variety of other sugary foods.
Even though they prefer food, however, silverfish aren’t picky when it comes to where they carb up. Silverfish commonly eat various fabrics, paper, glue and other adhesives, paper, book binding, photographs, and more.
Silverfish aren’t particularly motivated by food when it comes to where they choose to infest. Instead, they tend to eat whatever’s nearby, or they venture away from their nests to feed at night. Silverfish can even survive without food of any kind for very long periods of time.
SIlverfish prefer dark, moist, and cool locations. They’re commonly found near bathtubs, sinks, closets, basements, bookcases, storage areas, and other humid locations. The ideal temperature for silverfish is between 70 and 80 degrees Fahrenheit, with a relative humidity between 75 and 95 percent.
Silverfish avoid contact with direct light sources at all times. If they encounter light, they flee swiftly to the nearest dark cover. This behavior gives them their reputation for frightening people by darting away suddenly when encountered. They generally hide under dark cover during the day and forage for food at night.
Silverfish are capable of rapid movement. They can also change direction quickly to evade light or predators by crawling sideways at the same speed they move normally. Silverfish are characterized not only by their quick, somewhat jerky movements, but also by the way they move. When silverfish run, they appear to slither from side-to-side, almost like they’re swimming. This unusual running style and scaly, fish-like appearance led to the common name “silverfish” that most people know the pest by today.
Silverfish have surprisingly flat bodies that allow them to comfortably fit beneath very small enclosures. They often choose to squeeze into tight enclosures for the shelter and darkness they provide. Consequently, the pest is very commonly encountered beneath boxes, bags, furniture, rocks, piles of leaves or other vegetation, or in books.
Silverfish perform an elaborate, dance-like mating ritual each time they reproduce. During the “dance” ritual, a male silverfish releases his spermatophore (sperm packet) from a thread produced by the tip of his abdomen, near the filament. The female silverfish picks up the spermatophore and uses it to fertilize her eggs.
Once fertilized, the female deposits her eggs in cracks and crevices. Silverfish eggs are deposited in clusters of one to three. The female silverfish may lay several fertilized eggs after a single courtship over the course of several weeks. A single female silverfish may lay around 100 eggs in her lifetime, provided she is healthy enough and has a partner to perform the mating ritual with. In most indoor conditions, however, silverfish produce few young.
The speed of silverfish egg incubation and life cycle is determined largely by the temperature of the silverfish egg’s environment and the mating silverfishes’ access to resources. In ideal, warm environments, silverfish eggs may hatch in as few as 19 days and reach sexual maturity in weeks. In less advantageous environments, the hatching process may take up to 43 days or more, and may not reach sexual maturity for years.
Silverfish grow slowly, and must shed their skin or “molt” several times as they grow toward maturity. Immature silverfish look similar to their adult counterparts, except they are smaller and do not possess the pest’s distinctive silvery scales. Silverfish can live for two to three years, or even longer in humid and predator-free environments where they can easily access high-quality food.
Signs of Infestation
The most common sign of silverfish infestation is also the simplest: encountering one. Silverfish are often found when moving boxes, firewood, furniture, or other materials that may have remained stationary for long periods of time. Silverfish are particularly noticeable because of the speed with which they retreat to nearby darkness when encountered.
Silverfish may leave behind bite marks, waste, or shed skin behind on the food or clothing they infest. Though they can’t inflict significant damage, they may also chew through paper products, linen, adhesive, or other materials in their pursuit of sugary food materials.
Silverfish often climb into sinks, drains, showers, bathtubs, or other places where they can get moisture. Unlike so many other pests, however, silverfish aren’t particularly competent climbers. Often, after they get into a tub or sink, they can’t get out. Discovering dead or dying silverfish near plumbing fixtures may be a sign of nearby infestation.
When silverfish infest sensitive materials such as books or clothing, their waste and dead skin may damage them or promote mold growth. If books sitting on a shelf for long periods of time feel musty or soggy when touched, or clothing looks dirty or moldy, silverfish may be to blame.
Treatment and Prevention
Silverfish gravitate toward damp, moist, or humid areas. Sealing drafts, patching plumbing leaks, ensuring proper drainage and ventilation, and investing in a dehumidifier are all ways to reduce indoor humidity and make your building less attractive to silverfish and various other pests.
Silverfish dislike direct light and need to live in enclosed, sheltered, and dark areas. Deprive silverfish of as many potential hiding places as possible by storing packages, boxes, firewood, or other storage material off the ground, in sealed containers. Let natural light into rooms whenever possible, and keep naturally dark rooms like basements or attics clean.
Patch cracks around doors, windows, flooring, ceiling, and the foundation to deprive silverfish of hiding places, nesting sites, and possible access points all at once.
Removing food sources entirely may be difficult, but organizing or discarding old stacks of paper, cardboard boxes, piles of clothing, or various other clutter can help make your building less attractive to silverfish. Keep any food stored in your building in airtight, hard plastic containers, and elevated off the ground in a pantry, cupboard, or refrigerator.