When I was very young, I overheard one of my dad's friends telling him about a swimmer he had witnessed get attacked by a Portuguese Man o' War. In my youthful naivete, I pictured a Portuguese man in a military uniform coming out of the water and randomly attacking someone at the beach. When I asked my dad why such a thing would happen on a random summer day in Duck, North Carolina, and not somewhere in Europe during wartime long ago, he cleared a few things up for me. Portuguese Man o' War was just the non-scientific name for a particularly poisonous type of siphonophore. When I pictured this, I envisioned a Horseshoe Crab, and not the jellyfish-like creature roaming the high seas that bears the confusing name.
As a result of this seemingly harmless misconception, Horseshoe Crabs proceeded to creep me out ever since. I didn't think they served any useful purpose other than to look strange and continually freak out beach-goers (if either of those things could be considered useful). Turns out, they're life savers.
An interactive timeline on Wired.com discusses how a clotting agent known as Limulus amoebocyte lysate (LAL) is found in Horseshoe Crabs' blood. The substance binds to fungi and endotoxins, which allows scientists to detect impurities while testing various pharmaceutical drugs and medical supplies. Only a certain amount of companies are licensed to produce and sell LAL, and Wired takes you through the harvesting process that leads to the collection of LAL for testing. Turns out, our freaky-looking marine friends serve an extremely useful purpose. Who knew?
No Horseshoe Crabs were harmed during the making of this timeline.