Silverfish don’t bite, sting or spread disease, but they can cause damage to papers, some fabrics and some dry foods.
Although ominvorous in their diet (they will eat almost anything), their preference is for carbohydrates. In particular, they target plant material (silverfish are one of the few animals able to disgest cellulose) and starches. This means they can cause damage to paper, books, photos, wallpaper and glue!
They are of particular concern to homeowners, museums and other establishments that store books, papers and photos.
Silverfish tend to hide in dark, undisturbed placed, but if you find one, there’s more than likely to be many more.
There are around 600 species of silverfish that have been described, but there are likely many more.
Most of the silverfish homeowners will see belong to the family Lepismatidae, with the grey silverfish (Ctenolepisma longicaudata) being the most common silverfish in most countries.
Another interesting species is Thermobia domestica, which is prefers hot dry conditions and is sometimes found around ovens in bakeries.
There is also a whole sub-family of species which have adapted to live in the nests of ants and termites.
All species have a similar shape… they are a wingless insect with three tail filaments. The common grey silverfish, Ctenolepisma longicaudata, as its name suggests is a grey / silver colour with long tail filaments and equally long antennae.
They can grow up to 2cm long, have a flattened body that tapers towards the tail. Generally they are covered in scales, as is the case with the common grey silverfish, which will readily fall off when picked up or squashed!
Although they have no wings, they can run very fast, with a fish like movement, which is how they got their name.
In the natural environment, silverfish typically live in dry habitats such as dry leaf litter, under the bark of trees and under rocks. However, they do thrive in humid conditions (not wet), as they don’t drink, but absorb moisture through the air (through their bum!).
They are tolerant of quite large temperature ranges, being found in damp cool sub-floors and hot, dry roof voids. They don’t like light, which means they hide in dark undisturbed placed, allowing them to cause significant damage before they are noticed.
With their love of paper, they are often found in cardboard boxes, books, documents and roof insulation.
Silverfish undergo incomplete metamorphosis, which means although they moult regularly, their body form remains the same after hatching – baby silverfish look just the like adults, only smaller.
In fact, they continue to moult throughout their life-time as they get bigger. Moulting every 1-3 months, depending on conditions, they can moult up to 50 times during their lifetime, with sexual maturity reached after the 9th moult. In order to lay eggs they need to mate after each moult.
Silverfish undergo a mating dance before pairing up. There is no internal fertilisation, rather after the dance, the male lays a bundle of sperm and threads, which the female sits on!
The silverfish diet is primarily focused on complex carbohydrates such as cellulose and starches, which is why paper, cardboard and glue are readily eaten.
They only have small mouthparts so scrape the surface of materials. If they scrape enough, eventually they make holes.
The will also readily eat plant based textiles such as cotton and linen. Flour and rolled oats, being high in starch are also targeted by silverfish.
The do need some protein intake, so will eat insect carcasses. They will also eat wool and silk fabrics.
Silverfish are hard to spot, as they like the dark, undisturbed places such as the bottom of drawers or wardrobes. If you spot a large adult (over 1.5cm), you should realise it is probably over 2 years old and has been breeding for some time… so there is likely to be a lot more silverfish somewhere!
If you find silverfish in drawers or wardrobes, the first step is to painstakenly empty all drawers and wardrobes to look for more. Squash or spray any you see. You should then wash clothes in as hot a temperature as the clothes label allows to kill any silverfish eggs or adults you may have missed. Placing clothes in a black plastic bag in the sun is an effective heat treatment which will also kill any silverfish and their eggs.
Drawers and wardrobes should then be treated with a suitable insecticide. However, although this will prevent silverfish moving into those areas for some time, it is probable that you won’t have eliminated silverfish from your house, as they may well be in the sub-floor and roof void. This is when a professional silverfish treatment is beneficial.
In addition to treating internal areas such as wardrobes with a suitable product, professional pest managers will also treat roof voids with insecticide dust, and investigate whether a sub-floor treatment is required as well. They will also recommend actions to take to prevent a future infestation (see below).
There is also research into new silverfish control products including silverfish baits.
Most people will come across silverfish at the bottom of the sink or bath. Obviously there is no food in these locations, so why is this?
They don’t drink and so gain their water requirements by absorbing moisture through their rectum. Bathrooms and sinks tend to be high in moisture. As their legs are more claw like, they are unable to climb out of the baths and sinks, becoming trapped. They will also fall out of the down lights which are common in bathrooms.
More silverfish facts from Dr Graeme Smith
Other fabric pests.