Silverfish

This little silverfish Lepisma saccharina had a lucky escape last night when I rescued it in the nick of time from our bath. It lost a few segments from one antenna and from its tail cerci, but was otherwise intact - and very lively.

I hadn't seen one of these tiny, pewter grey, carrot-shaped wingless insects for quite a while. When I was a kid I used to see them racing out of dark corners of the kitchen cupboard, with their body undulating like a fish.

They like to feed on carbohydrates like spilled flour or sugar – the clue is in the saccharina part of their Latin name – and they also thrive on starch-based glue that holds some cardboard cartons together.

Silverfish like cool, humid places but their slightly larger and less common cousin, the firebrat, needs heat. It has lived alongside humans for as long as we have heated our homes with fire and was once common in bakeries. My grandfather, who worked for a major bakery firm in the 1920s, once told me that it wasn’t uncommon for them to be picked up in the dough and accidentally baked into loaves; not something that would earn Mary Berry’s approval in The Great British Bake Off.

These are some of the most ancient insects on Earth. Catch one, take a look with a magnifying glass and you’ll see that its carrot-shaped body is covered with these minute, overlapping, iridescent silver scales. These are easily shed and, together with their fast, wriggling motion, have allowed these living fossils to evade the jaws of predators for over 400 million years.

Silverfish

If you have a cupboard under the stairs, or kitchen cupboards that have dark, damp corners, then the chances are that you also have some of these silverfish Lepisma saccharina  lurking in them.  These primitive wingless insects belong to an order known as the Thysanura and are often thought of as being living fossils, having first evolved over 300 million years ago. They are covered with silvery scales that are easily detached and they also move fast, which makes them difficult to capture intact; this one has lost part of one of its three tail appendages and also the tip of an antenna. They are most active at night, emerging to feed on whatever organic material  they can find - spilled food, paper, even the glue from cardboard cartons. Sometimes they find their way into baths in bathrooms.

Although silverfish are present in most houses they don’t often produce severe infestations because the females only lay about twenty eggs during their lifetime, hidden in crevices until they hatch. They are, apparently, easy to maintain in captivity and will live for up to five years on a diet of damp paper and a pinch of flour, with regular access to moisture.

The first detailed description we have of a silverfish was recorded in Robert Hooke’s Micrographia or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries thereupon, published in 1665. 

The book contains this copper engraving of the insect, which is of stunning accuracy when you consider that Hooke observed it with lenses that he ground himself for his simple microscope – modern microscopists still marvel at his extraordinary skill and powers of observation. (You can see another example of his skill here).

Samuel Pepys was also mightily impressed and bought a copy of the book on publication, noting in his famous diary on 20th.January 1665 ‘took home Hook’s book of microscopy, a most excellent piece’.

Hooke called the silverfish ‘the small silver-colour’d bookworm’ and described, in his elegant prose, how ‘it appears to the naked eye, a small glittering Pearl-coloured Moth, which upon the removal of Books and Papers in the Summer, is often observ’d very nimbly to scud, and pack away to some lurking cranney, where it may the better protect it self from any appearing danger. Its head appears big and blunt, and its body tapers from it towards the tail, smaller and smaller, being shap’d almost like a carret’.

He described how it had ‘ conical body, divided into fourteen several partitions, being the appearance of so many shells, or shields that cover the whole body, every of these shells are again cover’d or tiled over with a multitude of thin transparent scales, which, from the multiplicity of their reflecting surfaces, make the whole animal appear a perfect Pearl-colour’ 

You can find pictures and information on the firebrat - the silverfish's larger but less common cousin - here and you can also view some other animals that share our houses with us here and here.