1 million hair per square inch – worlds furriest animal

Feb 20, 2015 • 4:41 PM UTC

San Pedro and Convention Center, San Jose, CA, USA

140x Magnification

Microorganisms

Manu Prakash

I am a faculty at Stanford and run the Prakash Lab at Department of Bioengineering at Stanford University. Foldscope community is at the heart of our Frugal Science movement - and I can not tell you how proud I am of this community and grassroots movement. Find our work here: http://prakashlab.stanford.edu

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Sea otters are amazing animals. They are cute, and so funny things but they have a tough life. Having almost no body fat, they co-inhabit cold waters with elephant seals (lots of fat) – so you wonder, how do they keep themselves warm. The answer lies in a beautiful evolutionary solution; make a lot of hair. I mean a lot. No really, a lot of hair. A sea otter is said to have 1 million hair per square inch on its fur. This is 1 with six zeros after the same. 1000000 hair packed in a tiny area of a square inch. The reason this helps keep them warm is how much air it packs inside this fur which is so thick that it does not allow water to penetrate and come touch the skin. So although you think a sea otter is wet, it’s in fact quiet dry. Isn’t that funny.
So this number was stuck in my head; and u always thought about which biologists actually counted this on a microscope. And one day, passing by the Marine Mammal center; I saw otter fur on display. Remember, sea otters in California were almost made extinct because of the value of the fur (which is sad – but now the population has made a comeback and we have a ban on fur use).
So I was delighted to actually have access to make a quick measurement of how thin is the otter hair. Before I make a measurement, let’s just do a simple calculation. 1 million hair (six zeros) in a square inch means 1000×1000 hair. Thus 1000 hair on one side of the square (which has a length of 1inch). So that means that the mean spacing between each hair is only 1/1000 inch which is only 25.4 microns. Wow – so the hair has to either 25 microns or even smaller. Remember, human hair is around 100 microns in width for reference.
So I asked the volunteers at the Marine Mammal rescue center to donate one hair each to this scientific cause. Also I took a scotch tape and stuck it on the fur and pulled gently, and I got a very small fraction of hair (nice trick for sampling)..
Here is the video that shows comparison between the otter hair and human hair from three different people. The perfectly black hair is mine, one white hair is from a 10 year old boy and one hair is from mammal center volunteer. We were so excited and laughing hard.. It was a lot of fun.

We learned not only that otter hair are small, but they have two different kind of hair. One really thin and one thick (almost the same thickness as human hair). Now, I leave this as a puzzle for you – what is the benefit of having two different hair thickness mixed in? Please leave a comment below. Next time you see a sea otter – respect.