Is It a Silverfish or a Firebrat?
By the Clark Pest Entomology Team
Last updated: October 28, 2026
Quick answer: Silverfish are shiny silver or pearl gray and like damp rooms such as laundry rooms and basements. Firebrats are mottled gray or brown and like hot spots near ovens, furnaces and hot water pipes. Both are about 1/2 inch long with three tail filaments. Check the room, then open the matching guide below.
Which One Did You Find?
Clark covers two look-alike insects that turn up indoors across California and Northwestern Nevada. Think about the room where you saw yours and tap the closest match.
Silverfish
Shiny silver or pearl gray and about 1/2 inch long. UC IPM says it likes damp, warm places such as laundry rooms. Look in bathrooms, basements, closets and bookcases.
Firebrats
Shiny and mottled gray or brown, also about 1/2 inch long. It likes very warm spots near ovens, heating units, fireplaces and hot water pipes.
Photo credits: silverfish by Christian Fischer via Wikimedia Commons, licensed CC BY-SA 3.0. Firebrat by David R. Madison via Wikimedia Commons, licensed CC BY 3.0.
Silverfish, Firebrat, Earwig, Centipede or Something Else?
Silverfish and firebrats have no wings and end in three tail filaments. Check your bug against each row. Details come from UC IPM and Penn State Extension.
| Bug | What it looks like | What it does | Where people find it |
|---|
| Silverfish | Shiny, silver or pearl gray. About 1/2 inch, up to 3/4 inch. No wings, three tail filaments | Scrapes paper and eats starch, glue and dry foods such as cereal and flour | Damp, warm places such as laundry rooms |
|---|
| Firebrat | Shiny and mottled, gray or brown. About 1/2 inch. No wings, three tail filaments | Same diet as silverfish | Near ovens, heating units, fireplaces and hot water pipes. Summer attics and winter furnaces |
|---|
| Earwig | Reddish brown and about 3/4 inch. Two forceps-like appendages at the tail | Feeds at night on seedlings, soft fruit and aphids. Can bite if trapped in clothing | Dark, cool, moist spots. Comes indoors when it is too dry, hot or cold outside |
|---|
| House centipede | Flat and brownish, usually more than 1 inch. One pair of legs on each body segment | Hunts insects at night. Some large centipedes can bite when provoked | Damp areas such as basements, closets and bathrooms |
|---|
| Carpet beetle larva | Hairy or bristly. Black carpet beetle larvae reach about 5/16 inch and taper to a tuft of long hairs | Eats wool, silk, leather, fur, feathers and pet hair | Dark, undisturbed places. Leaves brown, bristly cast skins |
|---|
| Booklouse | Tan, soft-bodied and wingless. Only 1 to 2 mm long | Feeds on mold and fungi. Does not damage paper directly | Humid, damp, dark areas |
|---|
A Silver Bug Just Ran Across My Floor
Look at the back end
UC IPM describes silverfish and firebrats as slender, soft-bodied and wingless, with two long antennae. The body tapers to three thin, tail-like filaments. If you see a pair of pincers at the tail instead, you have an earwig, and UC IPM says its appendages resemble forceps. If you see a flat body with many long legs, think house centipede.
Look at the room
Habitat does the sorting. Silverfish want damp, warm places at about 71 to 90 degrees F. Firebrats want very warm spots above 90 degrees F, and they do best at 98 to 102. A firebrat can live in air as dry as 30 percent humidity, which silverfish cannot. A silverfish at higher temperatures needs humidity above 75 percent. So a bug beside the water heater and a bug under the bathroom sink may not be the same species.
Look at the size and the hairs
At about 1/2 inch, these two are much bigger than a booklouse. Penn State Extension puts booklice at 1 to 2 mm. A hairy or bristly bug is not a silverfish. UC IPM says carpet beetle larvae are covered in hairs or bristles, and silverfish and firebrats carry dust-like scales. UC IPM also says both are nocturnal and dart to another hiding spot when you disturb them. Turn on the light fast.
Silverfish in the Bathtub, Sink or Laundry Room
According to UC IPM, these insects sometimes fall into bathtubs and sinks and cannot climb the slippery sides to get out. A tub sighting tells you where one fell, not where the colony lives. Firebrats crawl along pipes and through openings in walls and floors between levels. Large numbers can move indoors from surrounding areas as those areas dry out in summer.
Dry the room
UC IPM tells homeowners to fix leaks and drips, seal gaps around pipes and conduits, run dehumidifiers in closed spaces and use fans to lower humidity. It warns that large populations are nearly impossible to control while dripping water and moist surfaces remain. Check under sinks and behind washing machines first.
New build or remodel
UC IPM says silverfish can arrive in lumber and wallboard. Fresh concrete and green lumber add humidity, and wallpaper paste gives them something to eat. If they showed up after construction, ask your builder how long the materials stayed wet.
Holes in Books, Boxes or the Pantry
What the damage looks like
Their jaws are weak, so they scrape the surface of paper. On paper and fabric, feeding starts in one spot and spreads as irregular holes that do not connect. Fungi growing alongside can discolor pages. According to UC IPM, scales found near damaged items point to these insects. They eat cereals, flour, pasta and pet food, plus book bindings, wallpaper sizing and starched clothing. They can also go several months without food.
Rule out carpet beetles and booklice
Wool sweaters, fur and feathers point away from silverfish. Carpet beetle larvae feed on animal products such as wool, silk, leather, fur and pet hair, and leave brown, shell-like cast skins. Booklice feed on mold, and Penn State Extension says they do not directly damage paper. It says lowering humidity below 50 percent prevents mold growth.
Why spray alone fails
UC IPM says insecticides will not work unless you also remove the moisture, food and hiding places. It recommends saving chemicals for large infestations. It says baits are not very successful because these insects tend not to feed on them, and it does not recommend foggers. If control has not happened in 2 or 3 weeks, UC IPM says the insects are coming from an area you have not treated.
Clark's Expert Insight
Trap before you treat. Silverfish and firebrats travel long distances, so the source can be hard to find. Set sticky traps, or glass jars with tape wrapped around the outside, in corners and along edges for a few nights. Note which rooms catch bugs. Then follow the water for silverfish and the heat for firebrats. Treating where you saw one does not help if the hiding place is two rooms away.
Silverfish and Firebrat Questions Homeowners Ask
Do silverfish bite?
According to UC IPM, silverfish and firebrats have very weak jaws, so they scrape the surface of paper instead of biting it. If you wake up with bites, look at other causes. According to UC IPM, earwigs can bite if trapped in clothing, and some large centipedes can bite when provoked. See a doctor if a bite gets worse.
What bug looks like a silverfish?
A firebrat looks closest, and UC IPM says the two look alike. Earwigs, house centipedes, carpet beetle larvae and booklice get mistaken for them too. Check the table above. Silverfish have no wings, three tail filaments and a scaly, shiny body. Pincers, many legs or a hairy body mean it is something else.
Can silverfish be brown or black?
A brown one may be a firebrat. UC IPM describes firebrats as shiny and mottled gray or brown and silverfish as shiny silver or pearl gray. UC IPM describes black carpet beetle larvae as light brown to almost black with a tuft of long hairs at the tail, so look for hairs before you decide.
What does silverfish damage look like?
Look for irregular holes that do not connect, scraped paper surfaces and discolored pages. According to UC IPM, feeding starts in one area and spreads. Firebrat damage to paper can include large dark feeding spots and scales with fecal debris. Scales near the damage are a clue.
Are silverfish harmful?
They damage belongings, and the sources checked do not link them to illness. The University of Maine Cooperative Extension says silverfish are not associated with any diseases or the spread of disease. Penn State Extension calls them mostly a nuisance pest. They can harm paper, book bindings, wallpaper, cereal and starched fabrics.
Why do I still see silverfish after I sprayed?
Spraying does not fix the damp or hot spot that feeds them. According to UC IPM, insecticides will not work unless moisture, food and hiding places are removed. If control does not happen in 2 or 3 weeks, the bugs are coming from an untreated area. Find that spot and fix the water source.
When should I call a professional?
Call when you find them in several rooms, when traps keep filling after 2 or 3 weeks of cleanup, or when books or records are being damaged. According to UC IPM, many insecticides listing these pests on the label have not been adequately tested, and some products are limited to licensed applicators. A Clark technician can find the hiding place and treat it.