Horseshoe crabs have survived over 450 million years of toil and trouble, from Earth-changing asteroids to ice ages, but they might not survive the reign of the humans. Unfortunately, if this species really does reach an untimely demise, it could be a lot worse than a brief mention in the news; these prehistoric weirdos are extremely useful to us. 

Among their many, many weird traits, American horseshoe crabs (Limulus polyphemus) have copper-based blood that’s used to make limulus amebocyte lysate (LAL), a substance that’s freakishly good at detecting the presence of bacteria.

In the presence of gram-negative bacteria, the blood of the crab will set into a jelly-like blob because their blood cells (amoebocytes) coagulate around as little as one part in a trillion of bacterial contamination. As if its blood couldn’t get more bizarre, it doesn’t contain any hemoglobin, so it remains colorless when deoxygenated and blue when oxygenated. It's also worth noting that it isn't actually a true crab at all. It's not even a crustacean.

Scientists regularly use LAL tests, derived from the blood, in the food and pharmaceutical industries, as well as biomedical research, to sniff out the presence of bacteria. It’s still one of the main techniques used by industries to avoid wide-scale disease outbreak from bacterial contamination. A synthetic substitute is available, but nothing beats the real deal. According to Business Insider, the blood can sell for upwards of $60,000 a gallon.

However, these helpful freaks are under threat. The IUCN Red List, one of the more definitive authorities on wildlife health, states that the American horseshoe crab is vulnerable to extinction and on the slump.

Harvesting their blood no doubt plays a role in their demise. The Atlantic reported in May 2018 that at least 400,000 crabs are bled each year, killing an estimated 50,000 in the process. On top of this, they are faced with the same threats as much of the world’s marine life, such as warming waters and habitat destruction from climate change. They are also heavily commercially harvested for seafood bait, oddly enough.

As The Guardian reports this week, a major survey of these beasts will be published in spring 2019. In the meantime, scientists are predicting a 30 percent decline in population numbers off the east coast of the US in the coming decades.

So, the next time someone asks you why they should care about the plight of the world's biodiversity, point them towards the humble horseshoe crab. They ain't pretty, but you might owe them your life. 

[H/T: The Guardian]