The Diving Bell and the Spider
The water spider spends its life underwater but it needs oxygen to breathe. So when it visits the surface, the spider grabs a bubble of air that sticks to its hairy abdomen. It deposits this bubble into a little silk “diving bell” and breathes from the bell like a tank. The bell functions as a gill: as the spider removes oxygen from the bell, more oxygen flows in. Using a microscopic oxygen sensor, researchers from the University of Adelaide in Australia and Humboldt University in Germany determined how gases move across the bell's surface and found that the spider can stay underwater for up to 24 hours, they report this week in the Journal of Experimental Biology. The spider keeps the bell's volume proportional to its oxygen needs: To eat, it enlarges the bell, puts its food inside, and crawls in after it. Females lay their eggs inside the bell and enlarge it as the brood grows.