ZYGENTOMA | Silverfish 

Together with the Archaeognatha (bristletails), the Zygentoma (silverfish and firebrat) species are retained within the original subclass APTERYGOTA as they continue to be treated as insects in the true sense, whereas the remaining wingless hexapods, namely the Collembola (springtails), and the Protura and Diplura, are now placed in the ENTOGNATHA, which

is a separate taxonomic class that sits alongside INSECTA.

    

Although the Zygentoma order comprises five families with close on 600 species worldwide, only two have been traditionally listed as occurring in the UK; Lepisma saccharina (Silverfish) as featured here, and Thermobia domestica (Firebrat) which is only likely to be found indoors within particularly hot places such as bakeries. However, a few years ago a further species, Cteolepisma longicaudata (Grey Silverfish) was discovered and a further variant Cteolepisma lineata, a possible introduced pest species, has been noted, such that the current British List has now been updated to include all four species, all of which are placed in the Lepismatidae family.

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Without wanting to reminisce, I remember finding silverfish quite regularly when I was a child back in the late 50's and early 60's. They were often seen in the bathroom and occasionally in the old butler sink in the kitchen. Unlike firebrats, silverfish are only found in cool, damp habitats and although there are still many houses, particularly in rural areas, where such conditions are present, they are perhaps more likely to be found living in unheated outhouses even where there's a limited food source as they can survive for several months without feeding.

 

In certain subtropical areas of the world where silverfish survive in the wild, they are found in dark, moist habitats, living under rocks, dead leaves and tree bark. However, in Britain the humidity isn't sufficient so it would be quite exceptional I believe to find them outdoors. For that reason alone, I'd actually dismissed the chance of finding one, so was rather pleased to discover three or four under a box of ceramic wall tiles in a corner of my garage workshop whilst doing a bit of tidying up. Suffice to say that that job was temporarily put on hold until I'd managed to temporarily retain a couple so that I could take the photos seen here.

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Silverfish are relatively small, typically around 10-12mm, but occasionally a tad larger. They have a distinct compressed, teardrop shaped, slender body, wide at the front and tapered at the rear, which is covered in silver, fish-like scales. Darker coloured individuals though are not uncommon. They obviously have six legs like all insects and can run surprisingly fast, disappearing into small cracks and crevices in a blink of the eye. The abdomen has eleven segments ending in a 'tail' much like that seen in bristletails, comprising a central filament and a pair of cerci. They have mandibles, small compound eyes that can sense light, and long antennae that are used to negotiate their surroundings as well as acting as a highly sophisticated communication aid.

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They are nocturnal and rather skittish, with a long lifecycle, but relatively small home range.

 

Being members of the APTERYGOTA, silverfish go through ametabolous development rather than partial or complete metamorphosis as other insects. When they hatch, the nymphs look like small versions of the adult apart from the shiny appearance which takes a bit of time to develop, usually during their third moult. They can moult as many as 30-40 times during their lifespan and can live for anything from two to eight years in the wild depending on conditions, but in Britain I guess that it's more like two to four years.

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All species are known to feed on litter such as plant debris, but Lepisma saccharina will also eat cereals as well as paper and paper products, including wallpaper and books, so I suspect that the individuals featured here that I found in my garage were probably feeding on a combination of the cardboard boxes in which the tiles were stored as well as any bird seed that may have been accidently dropped whilst filling the feeders.