Dale Fort Blog Number 7

10 05 2012

The blog reverts from historical history to natural history and tells you much you might wish to know about  those unsung heroes of the three-tailed world:

 Silverfish

 
 A silverfish

Between 1985 and 1988 when I was privileged to live at Dale Fort, I developed a sleeping arrangement then revolutionary on The Dale Peninsula.  I spent each night on the floor, on a thin roll-upable mattress that I could pack away into a cupboard every morning.  Pioneering the futon meant I could maximise the floor area of my very small room during the few conscious moments I spent there when not teaching.  A secondary benefit was that I developed a close acquaintance with the thousands of silverfish who shared the accommodation.

 

Silverfish are members of a group of insects known as bristletails.  Moderately close inspection will reveal their three tails, the middle one being the longest.  They are not very large (maximum 15mm or so) and mostly harmless.  The reason I got to know so many of them by sleeping on the floor was because they tend to be inactive during the day, dwelling in crevices like the gaps between floorboards.  They emerge at night and run about very fast in search of food.

Their food comprises a wide variety of stuff.  In non-domestic situations they are found in woodlands, grasslands and on seashores feeding on algae, fungi, lichens and higher plants. (The seashore bristletail is called Petrobius.  It’s found on the upper shore and if you sneak up on it you can literally make it jump because it flexes its abdomen like a spring and bounces away).  They eat mostly dead material and help convert complex compounds into simpler substances that plants can absorb.  In jargon they would be called detritivores because they eat dead stuff (detritus).  Being fond of dead material they will chew on things like natural fabrics, paper, glues and wall-paper paste and so they may do some damage to fixtures and fittings.  They will also feast on the corpses of their friends and relatives (or indeed their enemies) given the chance.  This seems a little gruesome from our point of view but humans do it too in extremis and ultimately we are all detritus.

Bristletails are thought of as simpler than most insects but the males still indulge in ritual behaviour when it comes to reproduction (mind you, so do sea anemones and they’re simpler than any insect).  Fertilization is external but chaps do grab hold of girls to help ensure that sperm and eggs meet.  The males deposit a packet of sperm (spermatophore) on the ground and the female uses it to fertilize her eggs.  20 or so eggs are deposited in crevices and hatch any time up to several months later.  The female cannot store sperm and has to find a new packet every time she lays eggs.  The babies are miniature versions of the adults and moult about 8 times, sometimes over several years to become adults themselves.

Palaeontologists reckon that bristletails have been around for a very long time.  It’s believed that they have not changed much in the last 300 million years and can be thought of as an insect equivalent of the coelacanth but much older.  When the first fish-like vertebrates where crawling from the sea, they would have crept onto land already occupied by bristletails.  They are known to have been especially annoying to dinosaurs with ticklish toes and they’ll probably be around long after we’ve all disappeared.

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