Silverfish
Grey silverfish: how to identify them and what to do
A grey silverfish (Ctenolepisma longicaudatum), also called the long-tailed silverfish, is a grey, hairy relative of the common silverfish of 10 to 15 mm, with a speckled back and three tail bristles about as long as its body. The common silverfish is smaller, shiny silver and lives mainly in damp spots; the grey silverfish also lives in dry rooms, bookcases and lofts. It was first recorded in the UK in 2014 and is now found in homes across the country.
In this article
| Grey silverfish | Silverfish | Firebrat | |
|---|---|---|---|
| Latin name | Ctenolepisma longicaudatum | Lepisma saccharinum | Thermobia domestica |
| Length | 10 to 15 mm | 7 to 12 mm | 10 to 12.5 mm |
| Colour | greyish with a speckled back | shiny silver | dark grey, speckled |
| Hairs | hairy | hardly any | hairy |
| Tail bristles | about as long as the body | shorter than the body | long |
| Where in the home | also dry rooms, bookcases, lofts, between walls | damp: bathroom, kitchen, cellar | only very warm spots, next to a boiler |
| Lifespan | up to 7 to 8 years | 2 to 3 years | not given in our sources |
What is a grey silverfish?
A grey silverfish is a wingless insect from the order of bristletails (Zygentoma), the same group as the common silverfish. It avoids light, hides during the day in cracks of 2 to 3 millimetres and comes out at night. Young grey silverfish look like the adults but are paler.
What is the difference between grey silverfish and common silverfish?
The grey silverfish is larger, grey rather than silver, hairy and speckled, and has longer tail bristles than the common silverfish. The most useful difference is where you find it: the common silverfish needs a lot of moisture and lives in the bathroom and kitchen, while the grey silverfish also lives in dry rooms. If you see them in a bookcase, a bedroom or the loft, it is very likely a grey silverfish.
Is it a firebrat?
Probably not: a firebrat (Thermobia domestica) is a dark grey, speckled relative that only lives in very warm spots, such as next to a boiler. A silvery or grey insect in a bathroom, bedroom or bookcase is almost always a silverfish or a grey silverfish.
Why are grey silverfish spreading in the UK?
Grey silverfish travel with our belongings and thrive in warm, well insulated homes. The first UK record was in 2014, in a home in Reading; by 2021 researchers had records from England, Scotland and Northern Ireland, mostly in homes and flats, and they expect it to keep spreading. They think insulation and central heating give the insect the stable climate it needs. It comes in with packaging, removal boxes, second-hand books and furniture, and in blocks of flats it spreads through service ducts and cavities.
How long do grey silverfish live?
Grey silverfish live for up to 7 or 8 years, much longer than the common silverfish (2 to 3 years). At 24 °C and 60 % humidity it takes about 14 months from egg to adult. A female lays on average 56 eggs a year in batches of 2 to 20, which only hatch at a humidity of at least 55 %. Grey silverfish can go more than 250 days without food.
What do grey silverfish eat?
Grey silverfish mainly eat carbohydrates such as cellulose, starch and sugar, found in paper, wallpaper paste, books, cotton, linen and viscose. Now and then they also eat protein, including dead insects. Below 16 °C they stop eating.
Are grey silverfish harmful?
Grey silverfish are not harmful to your health in small numbers, and direct transmission of germs to people has never been recorded. In large numbers they damage wallpaper, books, stamps, posters, prints and clothes, and they do far more damage to paper than common silverfish. If you keep archives, a bookcase or a collection of papers, tackle them early.
How do you get rid of grey silverfish?
You get rid of grey silverfish by sealing their hiding places, keeping your home dry and not too warm, and catching the ones already there. Drying alone is not enough for grey silverfish, because they tolerate drier air than the common silverfish:
- Seal joints and cracks at skirting boards, pipe openings and sealant.
- Keep the humidity below 50 % and do not heat a loft or storeroom unnecessarily.
- Vacuum often along skirting boards and in cupboards, and clear piles of paper and cardboard.
- Store books and papers in plastic boxes that close.
- Put down traps where you see them, so you know where they come from. Whether the Super Ninja Silverfish Trap also catches grey silverfish has not been tested separately.
- Call a professional pest controller if they keep coming or are in several homes: in a block of flats the whole building often needs treating.
The full approach is in our guide how to get rid of silverfish, and our traps are in silverfish traps.
Sources: Kulma M. et al. (2021), Ctenolepisma longicaudatum Escherich (1905) became a common pest in Europe: case studies from Czechia and the United Kingdom, Insects 12(9), 810; Kennis- en Adviescentrum Dierplagen (KAD, Dutch knowledge centre on animal pests), knowledge base; Milieu Centraal; literature study by Wageningen University students for Super Ninja (ACT 2428, 2020), including Aak et al. (2019) and Eder (1940).
