Silverfish

Introduction

All members of the order Zygentoma have a teardrop/carrot/fish-shaped body and get the common name of bristletail because of their 3 long, bristle-like or tail-like appendages on the posterior/rear end of their body. Firebrat is the common name for those species which prefer areas of high temperature, 90°F (32.2°C) and above. Firebrats are found throughout the United States, and the world. 

Recognition

Adult body length, not including tails, about 1/2-3/4″ (12-19 mm). Wingless with flattened body. Shape teardrop/carrot/fishlike, tapering from head to rear, and generally covered with scales. Color silvery to gun metal, 1 species with dark lines running length of body. Antenna long, threadlike. Posterior end of abdomen with 3 long, bristlelike appendages (2 cerci, 1 median caudal filament). In addition, compound eyes small, widely separated; ocelli absent; coxae lack styli (fingerlike processes); tarsi 3- or 4-segmented; some abdominal segments with a pair of styli; abdominal sternites (underside of segment) lack median setal combs (tufts of hair) or if present, last abdominal tergite (upper side of segment) longer than wide; abdominal tergites with outer dorsal setal combs (tufts of hair) or if lacking, last abdominal tergite longer than wide.

Immatures similar to adults in appearance, except for size. Scales appear with 3rd or 4th molt.

Similar Groups

1. 1. Firebrats (order Zygentoma) lack silvery sheen, usually with mottled color, abdominal sternites (underside of segment) with median setal combs (tufts of hair) and last abdominal tergite (upper side of segment) wider than long.
   2. Jumping bristletails (order Microcoryphia) have large compound eyes which touch each other, middle, hind coxae usually bear styli (fingerlike processes), jump when disturbed.
   3. Diplurans (order Diplura) have only 2 appendages (cerci) at end of abdomen, body without scales, lack compound eyes, tarsi 1-segmented.
   4. Springtails (order Collembola) lack 3 abdominal appendages/tails but usually have a forked appendage at end of abdomen, lack styli on abdomen, antenna short.
   5. Larvae and wingless adults of insects with complete metamorphosis lack 3 bristlelike/taillike appendages on abdomen and styli on abdominal segments

Damage & Signs of Infestation

Feeding marks are irregular whether they are holes, notches along an edge, or surface etchings. Yellow stains, scales, and/or feces (tiny black pepper-like pellets) may be seen on infested materials

Representative Species

1. 1. Silverfish, Lepisma saccharina Linnaeus. Uniformly silver to steel gray to almost black, with metallic sheen; abdomen without setal combs (tufts of hair) on top but with median setal combs present on abdominal underside; adult body length excluding tails 1/2″ (12-13 mm); throughout the United States.
   2. Fourlined Silverfish, Ctenolepisma lineata (Fabricius). Scales dark gray with 4 dark lines running length of body; abdomen lacking median setal combs (tufts of hair) beneath but with setal combs above; with 3 pairs of styli (fingerlike processes) on rear of abdomen; adult body length excluding tails about 5/8″ (16 mm); eastern United States, southern California, Arizona, Nevada and Oregon.
   3. Gray Silverfish, Ctenolepisma longicaudata Escherich. Scales uniformly gray; abdomen lacking median setal combs (tufts of hair) beneath but with setal combs above; with 2 pairs of styli (fingerlike processes) on rear of abdomen; adult body length excluding tails about 3/4″ (19 mm); midwest, south, and southern California.

Biology

The silverfish (L. saccharina) female lays about 1-3 eggs per day, placing them in cracks, under objects, or left exposed. Egg hatch requires 72-90°F (22-32°C) and at least 50-75% relative humidity. Developmental time (egg to adult) is 3-4 months under favorable conditions, but may require up to 2-3 years otherwise. The majority live about 3 years. The most favorable conditions are 72-80°F (22-27°C) and 75-97% RH.

The fourlined silverfish (C. lineata) produces the enzyme cellulase in its midgut and can therefore digest cellulose.

The gray silverfish (C. longicaudata) female lays her eggs in batches of 2-20, placing them in cracks. The first instar lacks setae (hairs) and scales, scales appear in the 4th instar, and genitalia in the 14th instar. Sexual maturity is reached in 2-3 years and it may molt 3-5 times per year for another 5 years. Cellulose-digesting bacteria and enzymes are found in its midgut.

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Habits

All these silverfish species hide during the day and prefer to hide or rest in tight cracks or crevices. They can be found almost anywhere in a house including living rooms, bedrooms, bathrooms, attics, basements, garages, and shake roofs. Silverfish infest commercial structures such as offices, stores, and libraries. They tend to roam quite some distance while searching for food, but once they find a satisfactory food source, they remain close to it. Within structures, they can be breeding in a variety of areas, including wall voids, in/under the subflooring, attics, etc. Silverfish can survive for weeks without food or water.

Many species of silverfish are good climbers. Shake roofs are excellent breeding sites for silverfish during the warm weather months. Here, there is an abundance of moisture, cellulose, starch, and dead insects. From here, they can easily gain entrance and move down through the insulation to the sheetrock board with its glue and paper coating below. People notice them when they come down on ceiling soffits and/or drop from skylights and canister light fixtures in the ceiling.

Silverfish (L. saccharina) prefer areas of room temperature  (70-85°F/21-29°C) and high relative humidity (70-100%). They prefer proteins to carbohydrates and are cannibalistic. Silverfish are often introduced into buildings via cardboard cartons of books and papers from an infested location. They are pests of paper, particularly of glazed paper and paper with sizing, wallpaper and wallpaper paste, book bindings, gummed labels and envelopes, etc. Silverfish eat proteins such as dried beef and dead or injured of their kind.

The fourlined silverfish is not so limited by temperature and moisture. It may be found throughout a building, in the basement, in wall voids, the attic especially if the roof has wooden shingles, and in the garage. Outdoors, it occurs in the mulch of foundation flower and shrubbery beds, and under the bark of Eucalyptus trees in California.

The gray silverfish can be found throughout a building from basement to attic, but are not found outdoors. Often heat ducts and ventilators from the basement serve as avenues for widespread infestation. They survive well in both dry and moist conditions. Gray silverfish feed on carbohydrates and proteins of both plant and animal origin. They are fond of wheat flour and beef extract, especially when used as a paste on paper. Gray silverfish prefer papers of high chemical pulp content such as onion skin, cleansing tissue, cellophane (almost pure cellulose), etc., as opposed to newsprint, cardboard, and brown wrapping paper. They readily eat artificial silk, linen, rayon, lisle (long-strand cotton), and cotton, but not wools or true/natural silks; linen is most preferred.

Insect Control Naples

The key to control is identification which directs one to the preferred areas of habitation and food materials as outlined above. Identification is followed by a thorough inspection of preferred habitat areas and where appropriate food materials are present. If the infestation is localized on the inside, one can assume that it is recent and was either brought in via infested items or represents a recent invasion from the outside. Once the infestation(s) is found, selection of an appropriate pesticide and formulation is followed by a thorough application. Many infestations are very localized and environmental modification can greatly enhance control-e.g. controlling or eliminating moisture by repairing leaking pipes, sealing up easily accessible cracks and crevices, removal of potential food sources, etc. Dusts, especially inorganics, are particularly effective in wall voids, attics, crawl spaces, bathroom and kitchen fixture voids, subflooring voids, etc.

If the infestation is widespread, then attention should be directed to the outside. Silverfish can be found in firewood, wood piles, under debris piled up on the soil, in/under plywood and cardboard, etc. Anything stored against or very near the house’s exterior must be moved or removed since silverfish can easily climb up walls and find entrance around window and door frames, utility pipes, vents, fascia boards, etc. The cleared building perimeter can then be treated with an appropriately labeled pesticide. Be sure to treat up under the bottom row of any siding present.

If the shake roof is found to be infested, advise the customer to have it professionally and thoroughly powerwashed, and then water sealed; it should be resealed every other year. If the shakes are in poor condition and/or the customer cannot or will not have the shakes cleaned and sealed, then all of the crevices associated with the overlapping shakes and flashing will require thorough pesticide application, a very laborious process. If the infestation goes into the attic space, it may be necessary to pull back the insulation, treat underneath it with a long-lasting dust, and then put it back in place; perimeter areas including the roof overhang and wall studs below are critical and cannot be neglected.

Treatment for control of the fourlined silverfish will probably require treatment of foundation mulch beds and possibly the underside of shingles. Bookshelf treatment involves a thorough crack and crevice treatment of the bookcase itself, not treatment of the books. ULV treatment of heavily infested rooms is helpful in reducing numbers as is the use of a vacuum.