Spider heavyweights

October 11th 2019

Spider heavyweights

Early autumn is when long-legged house spiders sometimes invade our homes.  It is also the time of year when the heavyweights of the British spider world may be found.  Gwen Richards and I recently came across a couple of these during late season botanical recording.

On 8th September 2019, we were exploring the area behind Knockan (NC2109).  Just across the river from the impressive pothole Uamh an Tartair, we found a beautifully marked Garden Spider Araneus diadematus, spun up in heather (photos 1 and 2).  One of the orb-web spiders, it frequently occurs, despite its English name, out in the wilds.  It gets the alternative name of Diadem Spider from the cross-shaped pattern of brilliant white markings in the centre of the abdomen, contrasting with the dark brown ground colour.  A female, about 12mm in length, she was full of eggs (300-800), which would be laid shortly afterwards in a yellowish silken egg-sac located somewhere less conspicuous; this done her life’s work is accomplished.

Nearly a month later, on 2nd October, we were up behind Stoer village (NC0428), with Bill Badger.  Spun up in heads of jointed rush and purple moor-grass were two examples of a close relative, the Four-spotted Orb-web Spider Araneus quadratus, both females full of eggs.  The larger, shown here (photo 3), was 15mm long, and the heavyweight champion amongst British spiders.  In this species the ground colour is a variety of shades, from greenish-yellow to orange or red, ornamented with four large white spots, amongst other markings.  Females lay up to 900 eggs, a feat described by W.S.Bristowe, a classic observer of spiders in life, as ‘a record in childbirth’.

These two species are both widespread in Assynt, but don’t become obvious until about September.  The agile (and cautious) males mature a month or so earlier, in order to attempt mating.

Ian M. Evans

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