Horseshoe crab blood
On the evolution timetable, we humans are relatively the new kids on the block. We have been here in our current form for about 200,000 years. The horseshoe crab, however, has been here in almost the same form for roughly 450 million years. In all that time he has evolved some amazing defense mechanisms. His greatest feat, (at least in the opinion of humans) is developing blood with remarkable ability to detect bacteria. These animals spend most of their time close to shore, where bacteria is abundant. If they get even a slight crack in their shells, bacteria will invade. Their blood is able to find contamination in amounts as small as one part per trillion. Their reaction time to the infection is 45 minutes, not two days, like mammals’ white blood cell defense system.
For the last 50 years, the biomedical industry has been harvesting a quarter of a million horseshoe crabs a year, draining 30% of their blood and releasing them back into the ocean. Theoretically, most survive and replenish their blood supply in a month. The FDA has approved the use of this blood in detecting contamination in vaccines, implanted medical and dental devices like pacemakers and joint replacements. Some contamination from bacteria by-products can remain even after sterilization of scalpels, etc., and this quality checking method is far superior to any used in the past. In modern times, anyone who has a flu shot, an intravenous solution, or has their pet receive a vaccination, can thank a horseshoe crab for their safety. Not surprisingly, there’s a profit motive, too, since the blood sells for $15,000 a quart. Scientists have been scurrying around trying to find a synthetic alternative, but so far nothing has been good enough to earn FDA approval.
When the crab’s blood (which is light blue, by the way, although that nugget of info has nothing to do with the story) detects even a tiny presence of bacteria after a cut or puncture, it immediately forms a gel blob around the tiny invader. It doesn’t kill or expel the bacteria, but imprisons it in this impenetrable gel, where it can do no harm.
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