Wisdom of the Ancients: Horseshoe Crabs

Horseshoe crabs breeding

As an educator of sorts, I've learned to treasure the wisdom of my elders--the older they are, the closer I listen. So, when I happen upon a horseshoe crab, an animal whose ancestors have survived with few alterations to their anatomy or behavior for over 400 million years, I have to wonder what lessons it has to share. With my own species being a mere 4 million years out of the oven and already spiraling toward an uncertain future, I find myself gazing at the brown, birthday cake-sized shell like an oracle into a crystal ball; hoping to glimpse some of the answers I know it must hold in its ancient form. But where?

Maybe the key to its success is in its telson, the long, dagger-like spike protruding from the animals rear. What an amazing weapon! But when I pick a horseshoe crab up, I find that rather than trying to slash or jab me with its telson, it waves the appendage around with all the animosity of a dog wagging its tail. When I try to press my finger against the sharply pointed end, it simply wags it away. This animal’s first instinct is not aggression (sounds like ancient wisdom to me!). But that’s not to say they are defenseless.

When the time comes that it does need to defend itself, the horseshoe crab is ready with a row of inch long barbs. But, unlike most animals that put their most effective weapons up front (ex. teeth and claws) the horseshoe crabs barbs protrude from the rear plate that extends out on either side of the telson. Maybe the horseshoe crabs lesson here is, “cover your ass!” But we already know that, and look where it’s gotten us.

So I turn my attention to the eyes—maybe “the eyes have it!” While human researchers, in their anthropomorphic wisdom, consider horseshoe crabs to have “poor eyesight,” it seems significant that they have nine eyes and photoreceptors on their body. Five are located on the top of their shell, two are on their tail (remember the telson?) and there are even a couple on their underside near the mouth. Each of these light sensing organs is unique in appearance and function.

Eating while walking is another horseshoe crab talent. In fact, it’s a necessity. Being relatives of spiders (they're not crabs at all) they have long spider-like legs—ten of them altogether—which are covered with stiff bristles in their upper parts. These bristles grind (chew?) their food while the animal walks. It then it slurps the meal up with its "mouth" opening located at the axis of their ten legs. My son Niklaus is sure that the ability to eat and walk at the same time is key to the horseshoe crabs success. I have my doubts.

My money is on a small sensory organ on their back legs called the flabellum. Here, I must confess, my theory is based on nothing more than my love of a good metaphor. The flabellum, I’m told, is used to detect the quality of water before it enters the animal’s body through its respiratory organs, called the “book gills.” These are located just in front of the telson. What could better illustrate the folly of our current water policies than noting that horseshoe crabs have more wisdom under their tail than Florida politicians have under their hats.

As we go down the long list of the horseshoe crabs unusual attributes—their strange blue blood, their adaptation to bury their eggs above the high tide line, and others—it’s clear there is no one thing about horseshoe crabs that have allowed them to survive the ravages of time and the pressures of natural selection. Every time I pick up one of these living fossils, it seems I learn something new, about them and us.