Astronauts were hunting for a missing party guest as they prepared to celebrate the tenth anniversary of the International Space Station.

One of two spiders sent to the orbiting laboratory aboard the space shuttle Endeavour last week was added to the lost property list after the crew checked its tank and found it empty.

Anxious to quash fears that the absent arachnid may be marauding around the space station, Nasa managers insisted that the second orb-weaver was not exactly lost, it just couldn’t be found.

“We don’t believe that it’s escaped the overall payload enclosure,” assured Kirk Shireman, Nasa’s deputy space station programme manager.

“I’m sure we’ll find him spinning a web sometime here in the next few days,” he added hopefully.

Astronauts suspect that the spider may have simply gone for an impromptu spacewalk into its neighbour’s tank, though the pair were securely sealed off from one another at launch and were meant to spend their three-month research mission apart.

But the lead spider is so confused by the zero-gravity conditions that it has filled its tank with a tangle of silk to try to stop itself floating around and cure its space sickness, obscuring the search for the runaway.

The pair were prepared for their space adventure by scientists at the University of Colorado who hope to help answer schoolchildrens’ questions about how spiders spin webs in space. The answer would appear to be, ‘with difficulty’.

“The web was more or less three-dimensional and it looked like it was all over the inside of the spider hab\,” reported Sally Magnus, the expedition’s science officer, while mission controllers in Houston noted that the web is “more of a tangled, disorganised-looking web rather than the standard, Charlotte’s Web kind of web.”

The runaway spider, which was meant to be the back-up should the chief spider be incapacitated for any reason, was reported AWOL after Endeavour’s crew cracked open the cargo container containing its tank along with equipment including a new kitchen and toilet, additional living quarters for the station’s staff and a $250 million machine that will allow future crews to recycle their urine for drinking water.

Nasa and its international partners will today mark ten years since construction of the International Space Station began. Known as the most complex scientific and technological venture ever undertaken, it was built by a coalition of Nasa and the Russian, Canadian, Japanese and European space agencies.

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