How can spiders survive in water

Air bubble - Water spiders survive with the help of a diving bell

In contrast to their relatives, who spin nets in bushes or tinker through cellars, Argyroneta aquatica lives extravagantly. The "silver spider" is the only species of spider that can stay under water almost permanently. The animals spin their webs as a silky dome between the stalks of water plants. The animals then fill these diving bells with oxygen, which they carry down into the net as an air bubble on the long silver hair of their abdomen. Argyroneta spends most of her life in the dome - she even takes her egg cocoon with her into the silky building.

But how does the animal manage to keep enough oxygen available at all times? How often does it have to get oxygen from the surface? Roger Seymour from the Australian University of Adelaide and Stefan Hetz from the Institute of Biology at the Humboldt University in Berlin have now investigated this question under almost natural conditions. With a special application they were allowed to take some of the strictly protected water spiders from the river Eider and built a pond overgrown with plants for them in the laboratory. To make matters worse, there was no more oxygen than on a hot summer day.

A bell as a physical gill

Seymour and Hetz used special probes, the optodes, to check the oxygen content in the underwater network. “The previous literature assumed that the spiders had to come to the surface at least every 20 to 40 minutes during the day,” explains Seymour in the journal “Journal of Experimental Biology,” which published the results of the animal physiologists. Therefore, the researchers were more than surprised that their water spiders were able to live excellently with the available air. They use the bell as a physical gill. Even on a warm day, enough oxygen diffuses from the water into the network.

The trick of the spiders: they behave very calmly, so that their oxygen consumption decreases. "It is advantageous for the spiders to come to the surface only once a day and thus to be able to sit inconspicuously in the diving bell for most of the time for predators," the researchers explain. The spiders only go for air once a day to compensate for the volume loss caused by the escape of nitrogen.

Nicola Zellmer