Recognising silverfish: what do they look like?
I regularly get the question: “Johan, what are those little silvery bugs in my bathroom?” The answer: silverfish. They are not dangerous, but they are annoying. Let me explain how to recognise them.
The appearance of silverfish
Silverfish are quite unique in appearance, so if you see one, you will quickly recognise them. What do they look like?
Shape and size: 10-12 millimetres long (about one centimetre). Elongated, tapered body (wide in front, narrow behind). They look a bit like small fish - hence the name.
Colour: Silver-grey to metallic silver. Shiny scales on body. Juveniles are lighter, almost white.
Features: Three long hair wires at the back (two side wires and one middle one). Two long antennae at the front. Six short legs. No wings - they cannot fly.
How do they move?
This is probably how you first notice them: their typical movement. Silverfish move in a swaying motion - a bit like a fish gliding along the ground. Hence their name.
They are fast! If you turn on the light in the bathroom at night, you will see them flash away to dark places. They are light-shy and nocturnal.
Difference From Other Insects
Sometimes silverfish are confused with other small insects. Here the difference:
Silverfish vs paperfish: Paperfish are similar but darker (brown/black) and slightly larger. They mainly live in basements and have the same three hair threads. Both are harmless.
Silverfish vs cockroaches: Young cockroaches can look like silverfish. But cockroaches are rounder, have shorter antennae and no three hair threads at the back.
If in doubt: take a picture and app me. Then I can tell you what it is.
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Where can you find silverfish in your home?
Silverfish have specific preferences. If you know where they like to sit, you can find them more easily. And you can fight them better. Where do silverfish come from? Let me explain.
Bathroom: Their Favourite Spot
9 out of 10 times when people see silverfish, it is in the bathroom. Why? Moisture! Silverfish love high humidity (70-90%). And bathrooms are perfect after showering.
Where in the bathroom do you find them? Behind the washing machine, under the sink, in the shower cubicle (especially in the joints), behind the toilet, in cupboards under the sink, and between tiles and joints.
Check especially in the evening or at night. Turn on the light and look quickly - they will flash away to their hiding places.
Kitchen: At Moisture and Food
Kitchens are also popular with silverfish. Especially if there are leaks or lots of moisture. Where are they? Under the sink (when there are leaks), behind the fridge (condensation), in pantry cabinets with flour, sugar, paper, and behind kitchen cabinets against the wall.
Note: If you see silverfish in pantry cabinets, check your food. They like to eat starch, sugar and paper.
Other places
Less common, but also possible: Basement (damp and dark - ideal), attic (in case of leaks or insulation problems), laundry room (moisture from dryer/washer), and behind books in bookcases (they eat glue and paper).
General rule: silverfish are where it's moist, warm and dark. Combine that with starchy food (paper, cardboard, flour) and you have a silverfish paradise.
Where do silverfish come from?
I often get this question: “Johan, how did those silverfish get into my house?” Because they sometimes appear out of nowhere. Let me explain how they come in and why.
How Do They Get In?
Silverfish enter your home in different ways:
Through boxes and packaging: This is the most common way. You buy something in a shop, the box has silverfish or eggs, you bring it inside. Especially with books, cardboard boxes, and stuff from warehouses with moisture problems.
Via old stuff: Second-hand books, vintage furniture, old cardboard boxes from other people's attics - all potential sources.
Through cracks and holes: Silverfish can crawl through small cracks. Through pipe penetrations, cracks in walls and floors, and ventilation openings (especially in bathrooms).
From neighbours: In flats, they can come through shared pipes and walls.
Why Do They Stay?
Silverfish stay because they find with you what they need: moisture (high humidity), warmth (18-30 degrees - normal room temp), food (starch, sugar, paper, textiles, glue), and dark hiding places.
If your bathroom is always damp (poor ventilation), you have piles of paper or boxes, and it is nice and warm - then the silverfish hotel is open.
What Do Silverfish Eat?
This is important to know for control purposes. Silverfish eat: paper and cardboard (especially the glue), books (glue in the back), wallpaper (glue), flour, oats, sugar, textiles (especially cotton and linen), dead insects, and dander and hair.
They can survive for months without food. But with a good food source (e.g. a pantry full of boxes and paper), they multiply quickly.
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Are silverfish dangerous or harmful?
Let me give the good news straight away: silverfish are NOT dangerous. They do not bite, sting, or spread disease. But they can cause damage and are especially annoying.
No Health risk
Silverfish are completely harmless to humans and pets. They do not bite (they cannot even penetrate your skin). They don't sting. They don't spread bacteria or viruses. They do not cause allergies (unlike dust mites).
You can pick them up with your bare hands without risk (not that you want to).
Well Materiaals chade
Although they are not dangerous, silverfish can cause damage to belongings:
Books and paper: They eat holes in pages and eat glue from book spines. In large numbers, they can damage valuable books.
Textiles and clothing: They can eat holes in cotton clothes, curtains, sheets, and tablecloths. Especially items with starch stains (sweat, food).
Wallpaper: They eat the glue under the wallpaper. This can cause wallpaper to come loose.
Photos and documents: Old photos and important papers can be damaged.
Damage is usually limited, but when there is a large infestation over a long period of time, it can add up considerably.
Nuisance and Hygiene ne
The biggest problem? Nuisance. Nobody wants bugs in their house. It's unhygienic (they run over your toothbrush, laundry, towels). It's unpleasant (you turn on the light at night and see them scurrying away). And it's a sign of too much moisture (which can cause other problems, such as mould).
That's why you want to get rid of them, even if they are harmless.
Frequently asked questions about silverfish
I often get these questions about silverfish. Want to know more? Call for advice.
Silverfish are small, harmless insects that have been around for millions of years. They are 10-12mm long, silver-grey in colour, and have an elongated body with three hair threads at the back. They move swingingly (like little fish) and are light-shy. They mainly live in moist, warm places such as bathrooms. Scientifically, they are called Lepisma saccharina. They are completely harmless to humans - they do not bite, sting or spread disease. However, they can damage materials (paper, textiles, books).
Silverfish love high humidity (70-90%) and bathrooms are perfect after showering. They find everything they need there: moisture (from showering and bathing), warmth (bathrooms are often hot), food (dander, hair, soap scraps), and dark hiding places (behind cupboards, under the sink). If your bathroom is poorly ventilated and always remains damp, it is a silverfish paradise. Solution: ventilate better (window open, extractor on) and keep dry after showering.
No, absolutely not. Silverfish are completely harmless. They do not bite, do not sting, do not spread diseases, do not cause allergies, and are not poisonous. You can touch them with your bare hands without risk (not that you want to). The only problem: they can damage materials (paper, books, textiles) and they are a nuisance (nobody wants bugs in their house). But they pose no health risk to people or pets.
Silverfish enter through: boxes and packaging (most common - they are in cardboard from shops), second-hand books and stuff, cracks and holes (pipe penetrations, vents), and from neighbours (in flats through shared pipes). They stay because they find what they need: moisture, heat, food (paper, starch, textiles). Prevention: check new boxes before bringing them inside, ventilate well (low humidity), clean up paper and boxes, and seal cracks and holes.
Silverfish can get surprisingly old: 2-8 years! That's a long time for an insect. They grow slowly - it takes 3-4 months for them to reach adulthood. A female lays dozens of eggs during her lifetime (not hundreds like many other insects). They can survive for months without food. This means: a silverfish problem will not solve itself. If conditions remain good (moisture, warmth), they will stay and reproduce. Therefore, active control is needed.
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