Notes on Oedothorax retusus

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A Massing of Oedothorax retusus in South Devon by Peter Smithers

The Newsletter No. 60 March 1991

Whilst returning from a walk at approximately 5.30 on one Sunday afternoon in early March, I noticed what appeared to be a white polythene bag covering the top of a fence post beside the path, over which swarmed many 'ants'. Closer inspection revealed them to be spiders which I later identified as Oedothorax retusus. Examining the fence carefully it appeared that approximately 150 yards of it had been taken over by the spiders. Each fence post had a robust silken cap and bore between 100 and 200 spiders. The top strand of barbed wire was also enshrouded in silk and many spiders were moving along the wire to adjacent fence posts. I was curious to note that most of the spiders were moving in the same direction, which was easterly and slightly uphill. The grass beneath the central 60 yards of fencing was covered with dense sheets of webbing, but only the occasional spider was found there. Likewise the western end of the fence, although heavily webbed, was devoid of spiders.

Following the direction of movement, I discovered the most easterly section of fence had but minimal webbing and few spiders, all of which were still moving east. The fence ended adjacent to a small tree where a few spiders appeared to be trying to gain as much height as possible. Although the air at ground level was quite still, there appeared to be a good breeze at tree top height. Returning to the central section of fence I observed the spiders' behaviour for half an hour but witnessed only one attempt at ballooning.

As I was unable to return the next day, my son went to observe the phenomenon and reported low numbers of spiders on the fence. By the third day I was only able to find three moribund specimens over the entire fence. The fence formed the western and southerly boundaries of an area of rough pasture used to graze horses. If someone could throw some light on this massing of Oedothorax I would be extremely interested.
Added by John Partridge at 15:31 on Thu 29th Dec 2011. Return to Summary for Oedothorax retusus