I found a bit more info on this lurking in the depths of the internet, thought it might be useful:)
http://www.thefreelibrary.com/Firemen+left+in+a+spin...+by+a+spider?-a0105962626
"A SPIDER may have been responsible for bringing Cardiff city centre Cardiff city centre is a large and sprawling area that spreads out from Butetown in the south to Cathays Park in the north, and from Canton and Grangetown in the west to Adamsdown in the east. traffic to a standstill standstill /stand·still/ (stand´stil?) cessation of activity, as of the heart (cardiac s.) or chest (respiratory s.) .
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stand·still
n.
Complete cessation of activity or progress. .
The fire service was called to Castle Street on Saturday morning after an alarm was set off in an underground tunnel. And after fire was ruled out it was suggested that a spider crawled over a detection sensor - setting off the alarm.
The street was closed off from 10.20am to 11.30am as firefighters climbed into the BT cable tunnel in front of Cardiff Castle Cardiff Castle (Welsh: Castell Caerdydd) is a medieval castle and Victorian revival mansion, transformed from a Roman fort, in the capital of Wales. Roman forts
Main article: Cardiff Roman Fort
to investigate why the alarm had been activated. A fire was quickly ruled out but the investigation was made more difficult by the possible presence of asbestos.
As a precaution, firefighters wore protective clothing, entering the tunnel in pairs.
The tunnel, one of many under the capital, runs from Stadium House - BT headquarters - on Park Street to Cardiff Castle. The tunnels, built in the late 1970s by the then British Post Office to carry cables, are now redundant but the alarm system is still connected to Stadium House.
Assistant divisional officer John Bremner with South Wales South Wales south n → sud m du Pays de Galles Fire Service said: 'It looks a lot more than it is really and the location makes it interesting.
'There are a number of reasons why the alarm may have been activated. It could be a fault in the system or a spider could have crawled over the detection head.'
A spokeswoman for the fire brigade said: 'We were told there could be asbestos there, but we didn't find any sign of that.' "