Silverfish are a nuisance pest that can be quite annoying to deal with. As they rely more on their survivability and hiding instincts rather than on large numbers, they can be hard to spot. For that reason, it’s quite important to be able to tell the different types of silverfish apart when you see them so you can take the appropriate action immediately.
The Ctenolepisma genus, aka Silverfish, includes many different types spread out almost anywhere in the world. That’s not surprising as they are often credited as the oldest living land insect species on the planet. Most of them are outdoor insects and they aren’t even all classified yet as they can be quite similar in their characteristics and the outdoor types are not even viewed as pests.
As far as the common indoor silverfish species are concerned, however, there are only several you should keep in mind – the common silverfish (Lepisma saccharina), the four-lined silverfish (Ctenolepisma lineata aka Ctenolepisma quadriseriata), and the gray silverfish (Ctenolepisma longicaudata aka Ctenolepisma urbana).
The Gray silverfish
Also called big silverfish or giant silverfish, the gray silverfish (Ctenolepisma longicaudata aka Ctenolepisma urbana) is the largest household silverfish type. An adult gray silverfish can easily reach three quarters of an inch or a full inch under the right environmental conditions. When we say that silverfish can be up to an inch long, we mostly mean the gray silverfish.
As their name suggests, these silverfish are in a uniformly gray color that can be of slightly different shades of darker or lighter gray. It usually looks less silvery than other silverfish and depending on the lighting can look nearly black.
Gray silverfish prefer warmer temperatures that some of their brethren so they are less frequently seen in colder climates.
The Common silverfish
The Lepisma saccharina or the common silverfish is also sometimes called the long-tailed silverfish. It’s quite popular in North America and has a more silvery color than its giant counterpart. It’s typically about half an inch long and can tolerate a bit colder weather which is why it can often be seen even in the northern parts of the continent.
Aside from the size, color, and temperature-tolerance differences, the common silverfish behaves in a similar way to the gray silverfish – it eats the same things, reproduces in a similar fashion, and hides in the same locations.
The Four-lined silverfish
The third and last of the commonly found indoor silverfish types, the four-lined silverfish (Ctenolepisma lineata aka Ctenolepisma quadriseriata) is named this way because of its distinctive coloring. The adult specimens of this silverfish type have 4 straight black lines running down their backs. The overall color between the black lines is tan with a gray cast.
These silverfish are about half an inch long at most, just as their Lepisma saccharina brethren. Like the Giant silverfish, however, the four-lined insects prefer warmer climates and can’t be found too far north. As with all other types of silverfish, these two share the same diet preferences and hiding habits.
Are there any other common species of silverfish?
For Australians, it’s likely that you encounter another type of indoor silverfish – the Acrotelsella devriesiana. This common Aussie silverfish is about half an inch long as well and is slightly brownish in color. In terms of its diet and behavior, it is not dissimilar to its cousins from around the world.
Firebrats (Thermobia domestica) also deserve a mention here even though they are not technically silverfish. They are, however, members of a very close genus and resemble silverfish in many ways, including their body shape, as well as feeding, mating, and behavioral preferences. Their bodies are slightly darker and can often seem black. If someone is talking about black silverfish, chances are that they’ve encountered a Firebrat. Another key difference is that Firebrats prefer warmer temperatures which is why you can usually find them near boilers or furnaces.
How to distinguish between the different types of silverfish?
Silverfish are sneaking insects so they are hard to spot. If you ever see a living silverfish crawling about, chances are that you have a rather severe infestation on your hands or you were just “lucky” to stumble upon the intruder. If you indeed manage to see the silverfish in your home, looking for its distinctive visual characteristics is the easiest way to tell them apart.
If the insect is more than half an inch long then it’s most probably a Giant / Gray silverfish. If instead, it was about a half an inch long or less and had 4 black lines running through its shelf, then it was a four-lined silverfish. If not, it likely was a common silverfish.
If the insect looked nearly black and had distinctive darker patches on its back, it was likely a firebrat and not a silverfish at all.
If you haven’t had the chance to see the silverfish in your home directly but you’ve seen their silverfish droppings on your books or documents, then the easiest ways to find out what type of silverfish you’re dealing with is the check which silverfish are most common in your geographical area.
Silverfish come in lots of different sizes and types but the ones that commonly invade homes are just a few. They are more or less common depending on the geographical location, and despite their size differences they have more or less the same dietary and behavioral habits. They are also exterminated with similar means so in that regard it may not even matter that much which type you’re dealing with as long as you’re certain it’s a type of silverfish.