Horseshoe crabs are fascinating creatures—not just because they look like tiny armored aliens.
For starters, they aren't actually crabs. They're more closely related to spiders and scorpions than to lobsters or crustaceans. They also predate dinosaurs by millions of years, earning them the nickname “living fossils.” But perhaps their most famous claim to fame is their bright blue blood, which contains limulus amebocyte lysate (LAL), a substance that has been used for decades to test the safety of vaccines and medical equipment. (Fortunately for them, a synthetic alternative is now being used more often.)
Oh, and like scorpions, they glow under ultraviolet light—and scientists still don’t know why.
But one of the most remarkable discoveries about horseshoe crabs is that their brains have barely changed in over 300 million years. In 2021, researchers found a 310-million-year-old fossilized horseshoe crab in Illinois with its brain perfectly preserved. When they compared it to a modern horseshoe crab, they found virtually no difference.
Which makes a recent viral video all the more intriguing. Horseshoe crabs usually rely on their tails to flip themselves over when they get stuck upside down. But in the clip, one determined horseshoe crab seems to go out of its way to help a struggling companion who can’t right itself. The scene is surprisingly emotional—viewers have even commented that they found themselves tilting their phones as if they could assist in the rescue.
The video raises an interesting question: if horseshoe crabs' brains haven't evolved in over 300 million years, what motivates one to help another? Altruistic behavior is often associated with animals that have complex social structures, yet these ancient creatures appear to display it as well. Could it be a fluke, or have horseshoe crabs always had a built-in instinct to lend a helping… claw?
Regardless of the reason, watching one horseshoe crab refuse to give up on its friend is undeniably heartwarming. If a creature with a 310-million-year-old brain can show compassion, surely we can too.