Tuesday, 28 February 2012

Arachnaphobes look away now

I spent part of the weekend taking down an old shed that had reached the stage where new repairs would be pointless, the main structure rotten and unstable. As well as the pale shoots of ivy that had penetrated the crumbling boards, the shed held evidence of other lodgers. Two neatly made nests, each a mixture of moss, leaves and shredded plastic hinted at the presence of Wood Mice, something confirmed by the numerous Hazel nuts, carefully opened at one end by sharp teeth. There were woodlice in the damp corners and a huddle of snails in an old terracotta pot. It was the spider webs and their silent occupants that were of greatest interest, however, and these covered much of the wall space, particularly so in the corners and where uprights held the horizontal lapboard in place.

A few of the spiders were sizeable beasts; these were large Tegenaria house spiders of the sort encountered in the house during August or September, when the newly mature males wander in search of receptive females. The size of these arachnids makes them the bĂȘte noir of those suffering from arachnophobia but I find them rather engaging.

I could not be sure which of the eight Tegenaria species I was looking at, even though there were clear variations in size. Several can only be reliably identified through careful scrutiny under the microscope and hybridisation between species is rampant in some areas. The larger individuals seemed to occupy the largest webs, perhaps reflecting some variation in age since house spider webs are long-lasting. The silk used in these webs is not sticky, which may explain their longevity, and a web may be used by a succession of spiders over time as the original occupants die and are replaced.

The chances are that most of these spiders were females, since the mature males typically die early in the winter, having mated and leaving the mature females and immatures to sit out the cold weather. Come the warmer conditions of spring, the mature females should see an increase in prey availability and the resources needed to develop the eggs that will be deposited in a series of egg sacs. Each egg sac, made of white silk, is about the size of a small marble and may be decorated with prey remains; it will be deposited close to the web. I could not see any egg sacs, so I hoped that these spiders, about to be evicted from their current home, would find somewhere else to set up.

House spiders also occur away from human habitation, living under debris, within tree cavities or within rock crevices, but no doubt the replacement shed would soon be occupied.

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