Cobb County Extension Service
Horticulture

Silverfish

(Common Name: Silverfish)

(Scientific Name: Lepisma saccharina L.)

Identification

Silverfish are wingless, flat, silver to gray in color. They have tiny silver scales that usually give the body a metallic sheen.  Their bodies are ½ to ¾ inch long and taper carrot-like from head to tail.  Two long antennae extend from the head, usually wrapping around the body A familiar characteristic to insects from the order Thysanura (Common Bristletails), Silverfish have three long, slender “bristles” extending backward from the “tail” end. 

Firebrats are similar to silverfish but lack the silvery sheen.  They are brown to gray, with dark spots that give a mottled appearance.

Biology

Silverfish may take from three months to two years to develop from egg to adult, depending on the environment.  Firebrats usually take about four months.  Adults may continue to live for up to here more years and will molt throughout their lives, sometimes more than 30 times a year.  Eggs take 2-8 weeks to hatch.   Depending on the species, adults lay 5-50 eggs in clutches, in cracks and crevices near food sources.  The nymphs look almost identical to adults, except for being smaller and white.  Because their populations increase very slowly, large numbers indicate that there is a longtime infestation.

 

Habitat

Silverfish are found almost anywhere in the house but favor moist, warm locations – especially around sinks, other plumbing and undisturbed storage areas where the humidity is high.  They are frequently found in sinks or bathtubs because they fall in while seeking moisture and cannot climb out.  Homeowners often see them when they move storage boxes or open a cabinet door.  Firebrats prefer areas of high temperature (90 degrees and above) and high humidity.  They are more common in attics and around ovens, furnaces, water heaters and hot water pipes. 

Both silverfish and firebrats are most active at night and move swiftly, often stopping for short intervals before scurrying on. They move with a wriggling motion that reminds one of swimming fish. Both silverfish and firebrats are often initially brought into a home in paper, books, food, starched clothing or furniture.

Damage

These insects are considered pests primarily because they are a nuisance and an annoyance.  Silverfish feed on a wide variety of materials, including book-bindings, starch in clothing, linen, dried organic ornaments, wallpaper, magazines, paste and glue.  Though they may feed on various types of cloth, most often they are attracted to something that has spilled on the cloth, rather than the cloth itself.  Damage is significant, however, only in large infestations over long periods of time. They prefer carbohydrates and protein food such as flour, dried cereal, dried meat, rolled oats, paper and even glue.

Silverfish are primarily an indoor problem since they are rarely encountered outdoors. They usually are brought into the home in foodstuffs or other items such as furniture, old books and papers.

MANAGEMENT OPTIONS

Sanitation is a major step in controlling these pests. When storing items especially fabrics, be sure they are clean and starch free.  Keep in tight-fitting containers and reduce moisture as much as possible.  Because these pests often reside in wall cavities, keep storage boxes a few inches away from walls and raised off the floor. Sanitation only helps prevent a re-infestation after a population has been eliminated. It alone cannot control silverfish or firebrats and is only marginally effective in reducing their numbers.

However, a reduction in available water or relative humidity is helpful in eliminating silverfish and firebrats. Dry out or ventilate resting or shelter areas to reduce their moisture level. Since these insects prefer darkness, lighting a sheltered are a sometimes forces them to migrate to sites where they cannot survive or where they can be controlled more readily.

Chemical control: If sanitation alone is not sufficient, various pesticides may be useful in eliminating or reducing these pests.  Control may not be necessary if populations are low, limited to small areas and no damage is noticed. Available sprays for ants and roaches in pump sprayers or aerosol cans are usually effective. Contact your local Extension offices for recommended insecticides. Spraying outdoors is not particularly beneficial, but may help to reduce an occasional re-infestation. It is advisable to use the services of a pest control operator when the infestations are large, persistent and hard to find. A commercial operator has the knowledge, training and equipment to perform safe and effective control.

Also boric acid can be puffed into cracks and crevices and loosely around the storage area.  It has an advantage of being very low in toxicity and very long lasting if applied in dry voids where it will remain undisturbed.

Article by Laurene Hall, Program Assistant