Here’s something I didn’t know until recently: Pharmaceutical companies rely heavily on horseshoe crab blood to ensure that their products are bacteria free.

Here’s some other interesting things I learned:

1) Their blood is pale yellow or white and turns blue when exposed to air.

2) A single crab can be worth $2,500 over its lifetime for periodic blood extraction.

3) Although kind of freaky looking, they’re completely harmless to humans.

4) Horseshoe crabs possess the rare ability to regrow lost limbs.

5) Although not yet an endangered creature, horseshoe crab populations are declining.

Here’s the Wikipedia article, a neat article on the medical uses, and a nice general information site.