This is our native water spider, Argyroneta aquatica, which can still be found in some of the bog waters in our area. For years I have been taking care of a population of these animals, which - however - first crept into a large stainless steel tank. Meanwhile the spiders conquer one plastic container after the other, in which actually only Medaka are supposed to live. However - the spiders do not attack the fish and even fry grow up. I love our spiders and it is fun to watch them dancing through the water. - Friedrich Bitter