There are spiders that sail across the sea. And in Europe, the water spider lives, which even has its complete home under water. But these are exceptions among the approximately 50 000 known spider species. At least that's what was thought so far: the tropical spider species Trechalea extensa from Costa Rica, however, suggests that eight-legged friends may be visiting water bodies more often than suspected. Scientists led by Lindsey Swierk from Binghamton University report on this behavior in the journal "Ethology".
Swierk had observed how a representative of the big spiders fled people into the water and submerged there: a behavior that was not previously known from the species. The animal remained on the bottom of the water for 30 minutes, and while it was submerged, an air film passed its entire body. "The air film that surrounds the spider under water is apparently held together by hydrophobic hair that cover the entire surface of the spider," says Swierk. The film gives the spider look as if it had been dipped in liquid silver.
The air film could serve to keep the breathing openings away from the water, since spiders are air-breathing. It may also help to minimize the heat loss caused by the cold river water in which the spider is immersed, the biologists write. The European water spider, in turn, creates a kind of diving bell for itself: an air bubble, which it actively fills with air from the surface again and again, and which is held under water by a silk web.
However, water is not completely strange for the tropical relatives of the TreChaleidae spider family: they hunt prey from the country and in the water, but do not appear under - at least according to previous knowledge.
