Silverfish: Life Cycle, Effects, and Pest Control
Interesting and Annoying Creatures
Common silverfish (Lepisma saccharina) are small, wingless insects that wriggle as they move. They are interesting little creatures, but they can also be very annoying and destructive household pests. A major component of their diet is starch. Encountering the insects is often an immediate call to action in order to protect food, paper, and other starch-containing items.
Silverfish can sometimes be eliminated by natural means, which is always my preference. Chemical methods can also be used to get rid of them. After the insects have disappeared, a few precautionary steps will make another infestation unlikely.
How to Identify a Silverfish
A silverfish has an elongated and fairly flat body that tapers at the end. It has a segmented surface and is covered with shiny, silvery-grey scales. There are two long antennae at the tip of its head and three long bristles at the end of its body. The bristles are responsible for the alternate name "bristletail", which is used for both the silverfish and its relatives. Like other insects, a silverfish has three pairs of legs. Adults are a quarter inch to half an inch long.
As silverfish wriggle and move rapidly along the ground, it’s sometimes hard to see their thin, light-colored legs and appendages. This creates the illusion of little silver fish swimming on land and makes their common name very appropriate. The insects tend to move for a short interval, pause, and then move again.
Silverfish enter a house on their own or in a container such as a box that has been stored outside. They are pests and destroy property, but as far as researchers know they don’t transmit diseases.
The insects are usually found in damp areas with high humidity, such as basements, laundry rooms, bathrooms, and kitchens. They may be found in large numbers in new buildings if the plaster or wood in the buildings still contains moisture.
Silverfish are nocturnal creatures. During the day, they hide unnoticed in cracks and crevices. At night, they become active and search for food. They sometimes leave scales and yellow stains behind as they travel.
Since silverfish are secretive insects, they may reproduce and do a lot of damage before they're discovered. It's important to inspect dark and hidden places in a home regularly to determine whether pests are present.
Silverfish eat a wide variety of food, especially carbohydrates. They feed on paper, photographs, wallpaper paste, starch in clothes, fabrics such as cotton and linen, and any foods rich in carbohydrates that they find in the house. These foods include sugar, flour, bread, rolled oats, and other cereals. The insects even feed on starches in the glue found in book bindings.
Silverfish also eat mold, dandruff, and body coverings from insect molts. In addition, they eat high-protein foods such as meat and dead insects. They can survive for several months without food.
Silverfish Bodies and Egg Hatching
During the mating process, the male silverfish releases a package of sperm called a spermatophore onto the ground. The female picks the package up with an organ at her rear end called an ovipositor and then inserts it into her body. Sperm are released from the spermatophore and fertilize the female’s eggs.
The female lays the tiny eggs in any cracks and crevices that she can find. The eggs are white, oval, and about one millimeter long. They may hatch in weeks or months, depending on the environmental conditions. The nymph that is released from an egg looks like a smaller version of the adult, except it’s lighter in color and isn’t shiny. The nymph periodically molts (sheds its old body covering) as it grows. It eventually develops the dark and metallic shine that is a characteristic of the adult.
Silverfish are long-lived insects. They may live for two to eight years, depending on their environment. They continue to molt even when they are adults, which is unusual for an insect.
Silverfish may live for a long time if they aren't killed by humans or attacked by a predator. Common predators include earwigs, centipedes, and spiders.
Natural Pest Control
It’s best to avoid removing silverfish with pesticides unless chemicals are absolutely necessary, especially if you have children or pets. The fewer dangerous toxins in the home the better. A small to moderate infestation may be solved by eliminating the insect's food sources, preventing moisture buildup, and reducing humidity. A larger one may require trapping and disposal.
The following house cleaning and maintenance steps will help to solve a silverfish problem and may eliminate the pests completely.
- Repair any leaky pipes or faucets.
- Improve ventilation.
- Use a dehumidifier to reduce moisture in the air.
- Perform regular tidying, cleaning, and vacuuming to remove silverfish eggs and crumbs, scraps of paper, debris, and mold.
- Remove any uneaten pet food.
- Clean under sinks.
- Don’t forget to clean crevices too, such as around the base of ovens and refrigerators and along baseboards.
- Fill any cracks that you notice.
- Seal any areas where wallpaper has become detached from the wall.
Taking steps to avoid a silverfish invasion may also be very helpful for preventing infestations by other pests.
Storage of Food and Important Paper Products
Silverfish scales and droppings in food would be very unappetizing, to say the least. The destruction of irreplaceable family photos and important documents by silverfish would be heartbreaking. These effects can be avoided by the following strategies, which help to starve the insects.
- Make sure that all food containers and packages, photo albums, and containers of important papers are securely shut and sealed.
- Books, magazines, and newspapers should be placed in enclosed areas such as cabinets, cupboards, and plastic storage containers.
- Cupboards and containers should be cleaned to remove any silverfish eggs before paper products are stored in them.
- Make sure that cupboard doors and storage container lids close firmly, with no gaps, or seal them shut until silverfish have been eliminated from the home.
How to Trap Silverfish
Silverfish can’t move on smooth, vertical surfaces, so if they fall into sinks or bathtubs they will be trapped. A simple and effective insect trap can be made by covering the outside of a glass jar with masking tape and putting some bread inside the jar. The tape provides traction for the silverfish to climb up to the mouth of the jar. If the insects fall into the jar they will be trapped, since they won’t be able to climb up the smooth inner surface of the glass to get out.
If you need help deciding where to place traps, a technique that’s often recommended is to place index cards coated with a dried paste of flour and water in areas where you suspect silverfish activity. Leave the cards there for at least a week before you decide that none of the insects are present. Look for the appearance of notched edges and scrape marks on the index cards to indicate the presence of silverfish.
A Natural Pesticide
If you need chemical help to rid your house of pesticides, you might want to try diatomaceous earth first. This is a powder made of the crushed fossils of diatoms, which are microscopic creatures with hard coverings made of silica. The powder is abrasive and may remove the waxy covering on the surface of the silverfish. The coating helps to prevent water loss from the insect’s body. If a silverfish loses its waxy coating, it will dehydrate and die.
Diatomaceous earth is not toxic to humans or pets. It's important to be careful when using it, however, since the dust is a lung irritant. Wear a dust mask or respirator when you are applying the powder. Avoid getting it into your eyes or touching it, since in addition to being a lung irritant it's also a desiccant (a substance that removes moisture from materials).
Diatomaceous earth can be spread into crevices and pushed into cracks, but it may not be suitable for a house with pets. You really don’t want dogs or cats to sniff the areas where the powder has been applied or to inhale the dust.
A chemical pesticide may be necessary for a heavy silverfish infestation. The decision to use one should never be taken lightly, however. The pesticide may be applied as a spray or a powder.
Boric acid also kills silverfish, at least in some formulations. The acid is often reported to have very low toxicity in humans and pets when used in a dilute solution, but scientists have concerns about its safety as it becomes more concentrated. It's said to kill silverfish by dehydration and also by toxicity when it's ingested. Children and pets shouldn't have access to boric acid.
Pyrethrins are chemicals present in the flowers of specific species of chrysanthemums. They are classified as insecticides because they interfere with an insect's nervous system, killing the animal. They have low toxicity in humans and other mammals, however. They are often used in preference to more dangerous pesticides. I've never used pyrethrins, but they are said to work well in the fight against silverfish.
Pyrethroids are synthetic insecticides derived from pyrethrins. They last longer in the environment than pyrethrins and are often more toxic to humans. Different types of pyrethroids have been created. They have different characteristics and different degrees of toxicity.
If chemicals are needed to treat a silverfish infestation, it's best to consult a professional pest remover. Although pesticides can be very effective, there are potential dangers associated with them. This is especially true for some chemicals. An expert can remove pests and give safety advice as well.
A Silverfish Poll
Have you ever had silverfish in your home?
Firebrats: Silverfish Relatives
Some insect pests may be misidentified as silverfish. The firebrat (Thermobia domestica) is a relative of silverfish and may also be an unwanted guest in homes. Firebrats are similar in appearance to silverfish except for the fact that they don't have a silver body. Instead, their bodies are a grey or brown color and have black bands.
Firebrats live in warmer environments than silverfish. They can often be found around ovens, water heaters, and furnaces, especially in insulation. Like their relatives, they are pests and feed on carbohydrates, starches, and some proteins.
Silverfish and firebrats are closely related and belong to the Thysanura order of insects. There are about 370 species in the order. 18 species live in North America. Not all species in the order are pests.
Preventing a Future Infestation
Since silverfish aren't harmful to human health, there‘s no need to panic if you see a few of them in your home. A large infestation is more troubling, however, due to the potential property damage. A natural control method may be all that's needed to get rid of the pests.
Once the insects are eliminated or before they appear, good housekeeping techniques should protect a home from an invasion. Reducing moisture buildup, maintaining a clean home in good repair, and carefully storing food and paper products are good long-term strategies for making homes unattractive for silverfish.
Silverfish and firebrats in homes from University of Minnesota Extension
Silverfish and firebrats pest notes from the University of California
Facts about bristletails from PennState College of Agricultural Sciences
Information about pyrethrins from the National Pesticide Information Center
Pyrethroid fact sheet from Texas A&M Agrilife Extension
Integrated pest management for silverfish from the National Parks Service
© 2010 Linda Crampton