Silverfish in Spain – Why They Love Your Bathroom & How to Get Rid of Them (2026)

You switch on the bathroom light at 2am, half asleep, and a tiny silver torpedo darts across the tile floor and vanishes behind the toilet. It moved so fast you are not entirely sure you saw it at all. Then, a few nights later, it happens again — and this time there are two of them.

Welcome to the silverfish experience. If you live in Spain, you will encounter these insects at some point. They are in old village houses and modern coastal apartments alike. They are in Andalucia, Catalonia, Madrid, and everywhere in between. They are ancient, they are fast, and they have an unsettling knack for appearing at the worst possible moment. The good news: silverfish are completely harmless to your health. They do not bite, they do not spread disease, and they are not crawling over your food. The bad news: they can quietly damage your books, documents, photographs, and stored clothing if you let a population build up unchecked.

This guide covers everything you need to know about silverfish in Spanish homes — what they are, why they love your bathroom, what damage they can actually do, and how to get rid of them without calling in the professionals (though we will cover that too, just in case).

What Are Silverfish?

Silverfish (Lepisma saccharina) are one of the oldest insects on Earth. They have been around for approximately 400 million years — predating the dinosaurs by a comfortable 170 million years. To put that in perspective, silverfish were already well established when the first land vertebrates were still figuring out how to breathe air. They have survived every mass extinction event in planetary history. Your bathroom is not going to defeat them easily.

An adult silverfish measures 10-15mm in length, not including its appendages. The body is elongated, carrot-shaped, and covered in tiny overlapping scales that give it a distinctive silver-grey metallic sheen — hence the name. They are entirely wingless. At the rear, three long, tail-like filaments (called cerci) extend outward, and two long antennae protrude from the head. The overall appearance is unmistakable once you have seen one: a small, armoured, torpedo-shaped insect that looks like it was designed for speed.

And speed is their defining characteristic. Silverfish are extraordinarily fast for their size. When exposed to light, they sprint for the nearest crack or crevice with a darting, fish-like wriggling motion that gives them their common name. This speed, combined with their flat profile and ability to squeeze into tiny gaps, makes them very difficult to catch by hand.

Silverfish are strictly nocturnal. They are intensely photophobic — exposure to light triggers an immediate escape response. During the day, they hide in cracks, behind skirting boards, inside wall cavities, and under fixtures. They emerge after dark to feed, which is why almost every encounter happens when you switch on a light in the middle of the night.

In Spanish, silverfish are most commonly called lepisma or pececillo de plata (literally “little silver fish”). If you need to describe the problem to a Spanish pest control company or a neighbour, either term will be understood immediately.

Why Spanish Homes Are Perfect for Silverfish

Silverfish need two things to thrive: humidity and starch-based food sources. Spanish homes, particularly older properties, deliver both in abundance.

Mediterranean humidity

Spain’s Mediterranean climate creates ideal conditions for silverfish. Coastal areas from Catalonia down through Valencia, Murcia, and Andalucia experience relative humidity levels that regularly exceed 70% during the warmer months. Even in drier inland areas, bathrooms, kitchens, and poorly ventilated rooms generate enough localised moisture to sustain silverfish populations year-round.

Older property design

A significant proportion of the housing stock in Spain — particularly the properties that attract expats looking for character and charm — was built before modern ventilation standards existed. Thick stone walls, interior bathrooms with no windows, minimal or non-existent extractor fans, and poor airflow between rooms all create pockets of persistent humidity. The traditional tiled bathroom that stays damp for hours after a shower is a silverfish paradise.

Many older Spanish properties also have extensive use of tile grout, which contains starch-based compounds that silverfish actually feed on. The very material holding your bathroom together is a food source for them.

Storage habits

Expats in Spain often inherit or accumulate large amounts of paper, books, and cardboard in spare rooms, garages, and trasteros (storage rooms). In a climate where these storage spaces frequently lack climate control, you are essentially creating an all-you-can-eat buffet in a warm, humid environment. Silverfish will find it.

The combination of factors means that silverfish are not a sign of a problematic property — they are a near-universal feature of life in Spain, much like cockroaches and ants are universal features of Spanish kitchens. The difference is that silverfish operate quietly, out of sight, and many people share a home with them for years without realising it.

What Silverfish Eat

Silverfish are scavengers with a particular affinity for starch and cellulose. Their diet is remarkably varied for such a small insect, and understanding what they eat explains both where you will find them and what they can damage.

Primary food sources include:

• Paper and cardboard — newspapers, stored documents, cardboard boxes, envelopes
• Book bindings — the glue used in traditional bookbinding is starch-based and irresistible to silverfish
• Wallpaper paste — both the paste itself and the paper layer of wallpaper
• Clothing starch — natural fibres that have been starched or sized during manufacturing
• Cotton and linen fabrics — the cellulose content makes these vulnerable, particularly when stored in humid conditions
• Photographs — the gelatin coating on traditional photo prints is a food source
• Dead skin cells and dandruff — silverfish readily consume human skin flakes, which accumulate in bathrooms, bedrooms, and on upholstered furniture
• Damp cardboard — moisture softens the cellulose and makes it easier for silverfish to consume
• Other insects’ shed skins — including their own moulted exoskeletons
• Dried food residues — particularly anything containing flour or starch

This dietary range means silverfish can sustain themselves in almost any room of a Spanish home. A bathroom provides dead skin cells and damp grout. A kitchen offers flour residues and cardboard packaging. A spare bedroom with stored books and old documents is a permanent feeding ground. They are generalists, and that is part of what makes them such persistent household companions.

Damage Silverfish Can Cause

Let us be clear about the risk profile: silverfish are not a health hazard. They do not transmit pathogens, they do not bite humans, and they are not associated with allergic reactions in the way that cockroaches or dust mites are. The concern with silverfish is entirely about property damage, and for certain people — particularly book collectors, anyone storing important documents, and those with irreplaceable photographs — that damage can be genuinely significant.

Books and documents

This is where silverfish cause the most distress. They feed on the starch in paper and book bindings, leaving irregular holes and notched edges on pages. Damaged paper often shows yellowish staining around the feeding sites — a combination of silverfish excrement and the oxidation of exposed paper fibres. Over months and years, a silverfish population in a bookshelf or document storage area can render books unreadable and documents illegible.

For expats who have brought treasured book collections to Spain, or who are storing important paperwork (residency documents, property deeds, insurance records) in home offices, silverfish damage is not a trivial concern. Original documents are irreplaceable.

Photographs

Traditional printed photographs are vulnerable because of the gelatin coating on the image surface. Silverfish consume this coating, leaving the photograph surface cloudy, scratched, or partially destroyed. Digital backups are always wise, but many people have original prints with sentimental value that cannot be replaced.

Clothing and textiles

Silverfish can damage stored clothing, particularly garments made from cotton, linen, and silk. The damage appears as small, irregular holes — similar to moth damage but typically less extensive. Garments stored in humid wardrobes or drawers in infrequently used rooms are most at risk. Synthetic fabrics are generally safe, as silverfish cannot digest them.

Wallpaper

In properties with traditional wallpaper, silverfish eat both the paste and the paper itself, causing bubbling, peeling, and visible damage along edges and seams. This is less common in modern Spanish properties (which tend to favour painted walls) but remains an issue in older, traditionally decorated homes.

The important distinction is that silverfish damage accumulates slowly over time. Unlike a cockroach infestation, which becomes obvious within weeks, silverfish can work away at your belongings for months before you notice. Regular inspection of stored items is the best early warning system.

Where to Find Them

Silverfish are creatures of habit. Once you understand their needs — darkness, humidity, and food — their hiding spots become predictable.

Bathrooms

The bathroom is the single most common silverfish habitat in Spanish homes. Look for them under the sink, behind the toilet, in the gap between the bathtub or shower tray and the wall, and inside bathroom cabinets. Bathrooms in older Spanish properties — particularly interior bathrooms with no window and poor ventilation — can sustain substantial populations. The combination of constant moisture, tile grout (food), dead skin cells (food), and abundant hiding spots makes bathrooms ideal.

Kitchens

Silverfish favour the undersides of kitchen appliances (washing machines, dishwashers, fridges) where warmth, moisture, and darkness converge. They also hide around pipe penetrations under the sink and in the gaps behind kickboards at the base of kitchen units. Any area where food residue accumulates in darkness is attractive to them.

Laundry rooms

A damp, warm room full of textiles — laundry rooms tick every box. Silverfish are commonly found behind washing machines, in utility cupboards, and among stored cleaning products.

Bookshelves and storage rooms

Bookshelves in humid rooms are a serious risk area, especially if the books are tightly packed and rarely disturbed. Similarly, trasteros and garages used for storing cardboard boxes, old documents, and surplus belongings are prime silverfish territory. If you have boxes that have not been opened in a year or more, there is a reasonable chance silverfish have found them.

Behind skirting boards and in wall cavities

Silverfish are flat enough to squeeze into remarkably small gaps. The space behind skirting boards (rodapiés), around pipe entry points, and within wall cavities provides them with safe, dark, humid harbourage that is almost impossible to access without disassembly.

How to Get Rid of Silverfish

The good news about silverfish control is that it is almost entirely within your own hands. Unlike cockroach infestations that sometimes require professional intervention, silverfish can nearly always be eliminated — or at least reduced to negligible numbers — through straightforward DIY measures. The key principle is simple: remove humidity, and you remove silverfish.

Step 1: Reduce humidity

This is by far the most important step. Silverfish require relative humidity above 75% to thrive, and they cannot breed effectively below 60%. Your target is to get key rooms below 60% relative humidity consistently.

Practical measures for Spanish homes:

• Install or use a dehumidifier in rooms where silverfish are active. A basic portable dehumidifier costs €80-150 on Amazon.es and makes an immediate difference. Run it in the bathroom overnight and in storage rooms during the day.
• Use bathroom extractor fans religiously. Many Spanish bathrooms have extractor fans that nobody turns on. Run the fan during and for at least 20 minutes after every shower or bath. If your bathroom does not have an extractor fan, installing one is one of the best investments you can make — both for silverfish prevention and to prevent mould.
• Open windows for cross-ventilation whenever weather permits. Many Spanish homes are designed to be sealed against heat, but some airflow is essential for humidity control.
• Fix any leaking pipes or taps. Even a slow drip under the bathroom sink creates a permanently humid microenvironment that silverfish will exploit.
• Buy a cheap hygrometer (€5-10 at any ferreteria or on Amazon.es) and monitor humidity levels in problem rooms. You cannot manage what you do not measure.

In older Spanish properties with interior bathrooms and poor natural ventilation, humidity control requires more deliberate effort, but it is always achievable. This single step will do more than all other measures combined.

Step 2: Remove food sources

Once humidity is under control, the next step is to reduce the available food supply.

• Store books and important documents in sealed plastic containers with clip-down lids. This is especially important for items stored in spare rooms, garages, or trasteros. Clear containers are ideal because you can inspect contents without opening them.
• Remove cardboard. Replace cardboard storage boxes with plastic alternatives. Cardboard in a humid Spanish storage room is both a food source and a harbourage site — a double attraction.
• Clean regularly in hidden areas. Vacuum behind toilets, under sinks, behind kitchen appliances, and along skirting boards. Removing accumulated skin cells, dust, and food residues eliminates a significant portion of the silverfish diet.
• Vacuum cracks and crevices using a narrow attachment. This physically removes silverfish, their eggs, and food debris from hiding spots.
• Wipe up flour and food residues in the kitchen promptly, particularly around the cooker and on worktops where baking takes place.

Step 3: Trapping and treatment

With humidity and food sources addressed, targeted treatments mop up the remaining population.

• Sticky traps — Place commercial sticky traps (available on Amazon.es as trampas adhesivas para insectos) near known hiding spots: behind toilets, under sinks, along skirting boards. These are monitoring tools as much as control tools — the number of silverfish caught tells you whether your humidity control is working.
• Diatomaceous earth — This is the standout product for silverfish control. Diatomaceous earth (tierra de diatomeas) is a fine powder made from fossilised algae. It works by abrading the waxy coating on the silverfish’s exoskeleton, causing them to dehydrate and die. Apply thin layers in cracks, behind skirting boards, under sinks, and in any gap where silverfish travel. It is non-toxic to humans and pets but devastating to silverfish. Available on Amazon.es — search for “tierra de diatomeas alimentaria” (food-grade diatomaceous earth). A 1kg bag typically costs €8-15. For more detail on this and other products, see our best products guide, which covers diatomaceous earth and boric acid in depth.
• Boric acid powder — Another highly effective treatment. Acido borico is available at Spanish pharmacies (farmacias) without a prescription, typically for a few euros. Apply it as a thin powder in cracks, behind skirting boards, and around pipe penetrations. Silverfish walk through it, ingest it during grooming, and die within days. Keep it away from areas where children or pets could access it.
• Commercial baits — Silverfish-specific baits are less widely available in Spain than cockroach baits, but general insect bait stations placed in known activity areas can help reduce populations.

Step 4: Seal entry points

Preventing new silverfish from accessing your living spaces completes the control programme.

• Apply silicone sealant around pipe penetrations — every pipe that enters a wall in your bathroom and kitchen is a potential silverfish highway. A tube of silicone sealant costs a few euros at any ferreteria and takes minutes to apply.
• Fill gaps behind skirting boards — if there are visible gaps between skirting boards and the wall or floor, fill them with decorator’s caulk or silicone. This eliminates both harbourage and access routes.
• Seal around window and door frames where gaps exist, particularly at ground level.
• Check and seal gaps around extractor fan housings and ventilation ducts.

The combination of these four steps — humidity control, food removal, targeted treatment, and physical exclusion — will resolve the vast majority of silverfish problems within four to six weeks. You should see a noticeable reduction in sightings within the first two weeks of consistent humidity management.

Prevention for Spanish Properties

Prevention follows the same principles as control, applied proactively rather than reactively. If you are moving into a new property in Spain, or simply want to ensure silverfish never become a problem, these habits will keep you ahead.

Bathroom ventilation is critical. Many Spanish bathrooms — particularly in apartments — have no window at all. If yours has an extractor fan, use it every single time you shower or bathe, and leave it running for at least 20 minutes afterward. If your bathroom has neither a window nor an extractor fan, consider installing one. The cost is modest (€50-150 for a basic unit plus installation) and the benefits extend far beyond silverfish — it will also prevent mould and mildew, which are persistent problems in Spanish bathrooms.

Do not store cardboard in humid areas. This sounds obvious, but it is astonishingly common. The garage full of cardboard moving boxes that never got unpacked. The trastero with stacked delivery boxes. The spare bedroom wardrobe packed with shoeboxes. Every one of these is a silverfish habitat. Replace cardboard with plastic containers and your risk drops dramatically.

Use plastic storage containers for documents and books. Clip-lock plastic containers with rubber seals create a microenvironment that silverfish cannot access. They are inexpensive, stackable, and available everywhere in Spain — IKEA, Amazon.es, Leroy Merlin, or any Chinese bazaar (bazar chino). For particularly valuable items, add a small silica gel packet to the container to absorb residual moisture.

Regular cleaning of hidden spots. Build a habit of periodically pulling out the washing machine, vacuuming behind the toilet, and wiping under the bathroom sink. These are the areas where silverfish populations build unnoticed. Even a monthly clean significantly reduces the available habitat.

Monitor with sticky traps. Even if you have never seen a silverfish, placing a couple of sticky traps in the bathroom and near bookshelves gives you an early warning system. Check them monthly. If you start catching silverfish, address humidity before the population grows.

For a more comprehensive approach to household pest prevention, our pest prevention checklist covers silverfish alongside other common Spanish household pests in a single actionable document.

When to Call a Professional

Silverfish are one of the few household pests in Spain where professional treatment is rarely necessary. The DIY methods described above are effective for the vast majority of infestations, and most pest control professionals will tell you the same thing: fix the humidity, and the silverfish will leave.

However, there are circumstances where professional help makes sense:

• Severe infestation in a historic property — if you own or rent a property with extensive stone walls, numerous wall cavities, and limited access to harbourage points, a professional can apply residual treatments in areas that are difficult to reach with DIY methods.
• Silverfish damaging valuable books or documents — if you have a significant book collection, archival documents, or irreplaceable photographs at risk, a professional can provide faster results through targeted application of professional-grade products.
• Persistent problem despite humidity control — if you have consistently maintained humidity below 60% and removed food sources but silverfish remain active after two months, a professional inspection can identify harbourage points or moisture sources you may have missed.

Professional silverfish treatment in Spain is typically carried out as part of a general pest control treatment (desinsectacion general) rather than as a standalone service. Cost varies by region and property size, but expect to pay €80-150 for a standard treatment. For a more precise estimate based on your property, our cost calculator can help you understand what to budget.

When contacting a Spanish pest control company, look for a business that holds a DDD certification (Desinfeccion, Desinsectacion, Desratizacion) — this is the standard professional qualification for pest control in Spain. Ask specifically whether they use residual insecticides or dust formulations in cracks and crevices, as these are the most effective professional treatments for silverfish.

Silverfish vs. Other Spanish Household Pests

It helps to put silverfish in context alongside the other creatures you will encounter in a Spanish home.

Compared to cockroaches, silverfish are a minor concern. Cockroaches are a genuine hygiene issue — they contaminate food, trigger allergies, and reproduce rapidly. Silverfish do none of these things. However, the two pests share a preference for warm, humid environments, so if you are seeing silverfish, it is worth checking for cockroach activity too. The same humidity control measures help with both.

Compared to ants, silverfish are far less disruptive to daily life. You will never find a trail of silverfish marching across your kitchen worktop. They are solitary, secretive, and rarely seen in daylight. But while ants are mainly a nuisance, silverfish can cause genuine long-term damage to valuable possessions that ants typically would not.

The important takeaway: silverfish are a low-urgency pest. They do not require the immediate response that a cockroach infestation or a wasp nest demands. But they do require a response, particularly if you value your books, documents, or stored clothing. The longer a silverfish population goes unaddressed, the more damage accumulates — silently, in the dark, one tiny bite at a time.

Key Takeaways

• Silverfish are harmless to health — no biting, no disease, no food contamination.
• They are a property damage risk for books, documents, photographs, and natural-fibre clothing.
• Humidity is the root cause. Control moisture, and you control silverfish.
• Spanish homes are naturally vulnerable due to climate, older construction, and bathroom design.
• DIY methods — dehumidifiers, diatomaceous earth, boric acid, and sealing — resolve most problems.
• Professional treatment is available but rarely necessary — budget €80-150 if needed.
• Prevention is straightforward: ventilate bathrooms, store paper items in sealed plastic, and clean hidden areas regularly.