Underwater Spider Spins Itself an Aqualung 91
sciencehabit writes "In the ponds of northern Europe lives a tiny brown spider with a bubble on its back. The 10-millimeter-long Argyroneta aquatica is the only spider in the world that spends its entire life underwater. But just like land spiders, it needs oxygen to breathe. So every so often, it leaves its underwater web home to visit the surface and brings back a bubble of air that sticks to its hairy abdomen. It deposits the bubble into a little silk air tank spun for the purpose. This 'diving bell,' researchers have now found, is not just a repository. It's actually a gill that sucks oxygen from the water, allowing the spider to stay under for up to 24 hours."
Re:Only 24 hours? (Score:5, Informative)
here's a hint. the answer to your question is in the article
"The researchers decided to try out a new technology: a tiny fiber-optic oxygen sensor called an optode. Only 15 micrometers in diameter, the optode was small enough not to rupture the diving bell when the researchers poked it through the webby membrane and measured how gases move across the bell's surface. The bell, they found, functions like a gill: As the spider removes oxygen from the bell by breathing it in, more oxygen flows in to take its place. This gives the spider a constant oxygen supply without requiring it to venture to the surface often. But after about 24 hours.....
Re:Oh look... (Score:4, Informative)
Something that pops up again and again in various scientific and engineering endeavors is the "cube-square law". This law reflects properties that scale as area versus properties that scale as volume. In the case of the spider's osmotic sack, if we scale the sack up from spider size ( 1 cm ) to human size ( 2 m ), 200X, the sack's area increases by 200^2 = 40000 while the living being's body mass ( and presumably its metabolic activity ) increases by 200^3 = 8000000. If the sack's osmotic rate is just barely good enough for the spider, it is only 40000/8000000 = 0.005 of good enough for a human if both the sack and the human are scaled up by the same amount from spider-size.
To use a technology similar to the spider's for humans, it either has to be scaled up disproportionately or changed in some major manner (like pleating the sack, using forced water flow to provide more dissolved oxygen, using a better osmotic membrane, etc.