Raul Vicente discovered the tiny beast when he was studying bird migration and looking for spiders on the island of Landsort, the southernmost outpost of the Stockholm archipelago, in August.
“At first, I was sitting there with the spider and reacted to the fact that it looked a bit odd. I suspected it could be interesting. But then when I looked at it through a microscope, that’s when my pulse rose,” Vicente told Swedish news agency TT.
It turned out to be the sac spider Clubiona Juvenis, the first of its kind in Sweden. One of its notable features is that its mating organs are located near its face and look like tiny boxing gloves.
Sweden has 22 species of sac spiders, and Vicente believes that the Clubiona Juvenis may have been here for some time.
It is known to exist in the Baltics and Finland, as well as all of central Europe, and likely made it to Sweden by flying. When the spiders are hatched they are still very small and can spin a thread to let themselves be caught by the wind and thus travel far and wide.
Vicente has since found several more of the Clubiona Juvenis in the Stockholm archipelago which means it is unlikely to die out, and will probably grow its population in more parts of Sweden.
It is not thought to threaten any other species of spiders.