Common Silverfish (Lepisma saccharina)

Silverfish and firebrats belong to a very primitive group of soft wingless insects, evolving on earth even before the cockroach. They have a distinctive carrot-like form, long and slender, broader at the front end and gradually tapering to the rear. Their name is derived from the Greek: thysan, a fringe, and ura, tail. The fringe comes from the silver, flattened, hair-like scales scattered over the body and the "tail" is made up of three long posterior filaments. The young look very similar to the adults only they are smaller.

All silverfish and firebrats are vegetable eaters, some are subterranean or live in caves, and others are found in ant and termite nests. Most species remain hidden under bark or in leaf litter and require relatively high humidity. Of the 320 species of silverfish and firebrats found throughout the world, 18 species occur in North America. Of these 18, two species are major cosmopolitan pests, the common silverfish (Lepisma saccharina) and the firebrat (Thermobia domestica). Both of these species occur in domestic situations, feed on starchy materials and may be able to withstand considerable drying. They can also survive long periods without food.

Identification

Common Silverfish (Lepisma saccharina)

Uniformly silver to slate or pearl gray, ½ inch in length. These silverfish are a common pest in homes, libraries and museums where they eat paper, fabrics, and get into cereals. They have mandibles that can remove the sizing of paper in books, and magazines, damaging etchings and prints. They nibble on book bindings and feed on the glue and paste in the binding. This insect prefers cool, damp situations; their preferred temperature range is 72 to 80 degrees F with 72 to 95% relative humidity. The common silverfish can live for as long as two years and may molt up to 50 times during this period. There are other species of silverfish that may also be present and their identification, biology and control are similar.

Firebrat (Thermobia domestica)

Mottled gray to tan in color, with tufts of brown setae, ½ inch in length. This species prefers to feed on paper and paper products, such as books with a glazed finish. This insect prefers the warmer situations around furnaces, boilers, and steam pipes. Temperatures of 90 degrees to 106 degrees F are in the optimum range. This insect lives from one to two years and can molt more than 50 times during this period. Injured appendages are regenerated throughout life.

Biology

If you see silverfish or firebrats running over the floor, you can be sure there are more specimens lurking behind the walls, in voids of shelving and under baseboards. Their eggs are very small, often laid in cracks and crevices and are carried into buildings along with cardboard boxes and other shipping containers. A single female may lay less than 100 eggs during her lifetime of 2 to 3 years. These insects are primarily nocturnal and will quickly retreat into hiding when lights are turned on. In general, silverfish are found at the floor level and on shelving. Moist, dark areas make the most attractive habitats. Firebrats are found around furnaces, boilers, and hot water pipes.

Evidence of Damage

• Book bindings show minute scrapings. The sizing of paper is removed in an irregular fashion and the edge of the paper presents a notched appearance. Where the damage is severe, irregular holes are eaten directly through the paper.
• The small dark feces of silverfish and firebrats are visible to the eye, and their scales can be identified with a hand lens.
• Sticky survey traps can be set out to capture specimens for verification of species. These traps will also help to locate how pests are entering an area. Firebrats are often trapped as they enter a room from radiator pipe openings. Traps can also be used to measure the success of control measures.

Control

There is normally considerable difficulty in eliminating silverfish or firebrats, most infestations are chronic and are seldom resolved completely. However, in many situations it may be possible to tolerate a low level of these pests. If chemicals are the basis of a control program, the accumulation of dead carcasses and their scales over time may create other problems including allergies. Dead insects are a food source for carpet beetles, so the area should be thoroughly vacuumed. Under ideal circumstances, it is best to change the environmental conditions that allowed the population to exist in the first place.

The following steps are effective in reducing populations of silverfish or firebrats over time:

• Eliminating moisture in the immediate vicinity of an infestation. Dry out an area and keep it dry. Using desiccants such as silica gel in the microhabitat may accelerate this drying process. Frequently the installation of moist wallboards in new construction projects will introduce silverfish into an area.
• Prevent access to food, especially starch containing materials such as paper. Enclose in tightly sealed containers if possible. Another method is to use sticky tape or chalk barrier to prevent silverfish or firebrats from climbing up the legs of equipment.
• The use of heat, especially for the common silverfish, and cold for the firebrat will reduce populations significantly. By maintaining a room at a temperature consistently below 60 degrees F, both species will be discouraged from breeding.
• If environmental conditions cannot be altered, and they are ideal for firebrat development (warm temperature and high moisture with lots of cracks and crevices) then a combination of traps and baits may help reduce populations to acceptable levels.
• It is always a good idea to improve sanitation by picking up accumulated debris, drying out the area and removing any potential sources of food.