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Silverfish are the small, silvery insects that dart for cover when you switch on the bathroom light at night. They do not bite and they do not spread disease, but they graze on paper, books and wallpaper, and a growing number of homes are finding a larger relative, the grey silverfish, which is harder to shift.
What do silverfish look like?
The common silverfish (Lepisma saccharina) grows to about 10 to 12mm. It is flat and carrot-shaped, tapering towards the tail, and covered in silvery scales. It has two long antennae at the front and three bristly tails at the back, and moves in quick, wriggling bursts that look a little like a fish.
The grey silverfish (Ctenolepisma longicaudata) is larger, up to about 15mm, greyer and duller, with noticeably longer antennae and tails. It has spread in UK homes in recent years and is often found in newer, well-heated houses, including rooms that are not damp at all. It is thought to travel in cardboard packaging and stored paper.
Firebrats, a related species, are browner and like warmth. They are sometimes found around boilers, ovens and commercial kitchens.
Where do silverfish live?
Common silverfish need high humidity, so you will usually find them in bathrooms and kitchens, under sinks and baths, in cellars and around leaks. They hide by day in cracks and crevices: under skirting boards and floor coverings, behind wallpaper and boxes, and inside stacked paper and books. They come out after dark to feed.
Grey silverfish are less fussy and turn up in living rooms, bedrooms and offices, often in the same places as stored paper and cardboard.
Are silverfish harmful?
Not to people or pets. The concern is what they eat. They feed on carbohydrates and protein, including:
- paper, books, photographs and stored documents
- wallpaper and wallpaper paste
- book bindings and the glue on cardboard boxes
- cereals, flour and food crumbs
- mould, dead insects and skin flakes
The damage is usually surface grazing, small irregular holes and yellowish marks, and in most homes it is minor. Where paper, books or photographs of value are stored somewhere damp, it can add up over time.
Signs of silverfish
- Silverfish seen at night, especially when you turn on a light in a bathroom or kitchen.
- Grazed or holed paper, wallpaper or book covers.
- Tiny dark droppings, like pepper, near where they feed.
- Shed skins and fallen scales in drawers, on shelves and among stored items.
What you can do
- Reduce humidity. Use extractor fans in bathrooms and kitchens, ventilate after showering and cooking, fix leaks promptly and run a dehumidifier in problem rooms. This alone deals with most common silverfish.
- Declutter. Clear out piles of newspaper, magazines and cardboard boxes, especially in cellars, lofts and under beds.
- Store paper and books sensibly. Keep valued documents and photographs in sealed plastic boxes rather than cardboard, in a dry room.
- Vacuum regularly, including along skirting boards, in cupboards and under furniture, to remove crumbs, eggs and the silverfish themselves.
- Seal hiding places. Fill gaps along skirting boards, around pipes and at the edges of floor coverings.
- Keep dry food sealed in airtight containers.
- Check deliveries. Unpack parcels promptly and do not store cardboard boxes in living areas.
Sticky monitoring traps are useful for showing where silverfish are most active and whether numbers are falling.
When to call us
Silverfish are hard to reach because they live in so many small spaces: under floors, behind skirting boards, inside walls and among stored belongings. If you have dealt with the humidity and are still seeing them, or you think you have grey silverfish, which do not respond to drying out in the same way, send us a photo. We identify the species, find where they are concentrated, and treat those areas, with advice on the changes that keep them down.