The spider has disappeared after arriving at the station aboard the shuttle Endeavour.
Nasa says the female spider, one of two sent to the orbiting laboratory as part of a science experiment, appeared to have escaped during transit.
The second spider is so confused by the zero-gravity conditions that it has filled its tank with a web to try to stop itself floating around.
This means astronauts cannot see into its tank to check if the other spider has hidden in there with it.
Kirk Shireman, Nasa's deputy space station programme manager, said: "I'm sure we'll find her spinning a web sometime here in the next few days."
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http://www.metro.co.uk/news/world/article.html?Astronauts_lose_spider_in_space&in_article_id=411382&in_page_id=64
