Silverfish and firebrats belong to the insect order Thysanura. These insects differ from most other insects by continuing to molt, or shed their exoskeleton, throughout their entire lives.
Silverfish and firebrats are usually considered a nuisance when they invade homes. They consume and stain books, fabric, foods and wallpaper. These insects prefer starchy foods such as flour, rolled oats, paper or glue. Damage is only significant if a large population is present for a long period of time.
Biology and Description
Silverfish and firebrats have flattened elongate bodies that taper at the end like a carrot. They have chewing mouthparts, long antennae, no wings and three tail-like projections at the end of the abdomen. Fine scales cover their bodies. Silverfish and firebrat immatures look like the adults, only smaller in size.
Silverfish and firebrats typically run quickly and are mostly active at night. In homes, they are commonly found in closets, attics or near bookcases and hide behind baseboards or casings around doors and windows.
The silverfish (Figure 1), Lespisma saccharina (Linnaeus), is probably the most important pest species of Thysanura. Silverfish like temperatures between 70-80 o F with a relative humidity of 75-95%. Females lay eggs singly or in batches either daily or at irregular intervals depending on food availability. Eggs hatch in about 40 days with low temperatures (about 70 o F) or 20 days with high temperatures (about 90 o F). Silverfish may molt up to 60 times in their lifetime, which is usually about 2-3 years.
Figure 1. Silverfish, Lespisma saccharina (Linnaeus).
The firebrat, Thermobia domestica (Packard), is similar to silverfish, but is mottled brown. Firebrats prefer temperatures over 90 o F and therefore are often found near ovens, dryers or hot water heaters. Eggs are laid in batches with an average of 50 per batch. Under good conditions, the eggs hatch within 13 days and the nymphs begin to their development. Firebrats may molt 50 to 60 times during its lifespan which can be up to 2 years in warm areas.
Sanitation should be used to avoid infestations of silverfish and firebrats. It cannot be used as the only means to eliminate infestations. Remove old books, magazines and newspapers. Inspect fabrics that have been stored for long periods for damage or infestation. If books or fabrics will be in storage, store these items in sealed plastic containers. Many times valuable books or papers have infestations of silverfish. These items can be placed into a sealable plastic bag and placed into the freezer for several days to kill the silverfish.
Clean closets on a regular basis to help remove harborage areas. Vacuum regularly and clean up spilled food or drink immediately. Make sure to inspect any items brought into the home, especially those that have been in storage, to avoid an infestation.
In areas of infestation, or areas where books are stored, reduce humidity by using air conditioning units, fans or dehumidifiers. Repairing any plumbing leaks will cut off water sources for these insects.
Insecticide treatments should be targeted to harborage areas such as cracks and crevices, around baseboards, closets and attics. With large infestations, small holes may be drilled in walls to treat the wall void.
Look for products labeled to control silverfish, firebrats or bristletails. Natural active ingredients include d-limonene, clove oil, thyme oil, boric acid or diatomaceous earth. Synthetic active ingredients are items such as bifenthrin, lambda-cyhalothrin, cypermethrin, permethrin or deltamethrin.
Formulations of the above mentioned products may be baits, dusts, or aerosols. These formulations should be used in crack and crevice treatments, in attics, wall voids and other areas inaccessible to children and pets. Dusts should be used with care, and should not be inhaled as they are being applied.
It is advisable to use the services of a pest control operator when the infestations are large, persistent or hard to find. A commercial operator has the knowledge, training and equipment to perform safe and effective control.
Insecticide label clearances are subject to change and changes may have occurred since this publication was printed. The pesticide USER is responsible for the effects of pesticide residues on plants or household goods, as well as problems that could arise from contamination of neighboring properties or plants. Always read and follow carefully the instructions on the container label.
The authors wish to thank Kim Engler and Alan Brown for review of this manuscript.
Photograph by Bastiaan “Bart” M. Drees.