Not so yummy?

Two common questions I get about animals: what do they eat and how do they eat it?

The horseshoe crab doesn’t have a mandible, or jaw, and neither does it have teeth.  This is fairly common in the non-mammal animals.  Instead, the horseshoe crabs crush their food between their legs before they pass the crushed food into their mouth or gullet. Their mouth or gullet is located at the top of their body.  From there the food is passed to their stomach.

The gullet is also known as a gizzard in bird species.  The purpose of this thick sac with muscular walls, also known as a secondary stomach, is to grind up the food before the food is eaten.

This gullet is important because horseshoe crabs do eat clams and mussels as well as worms, algae, and carrion (dead flesh).  Unlike shorebirds, the horseshoe crabs don’t crack the shells open, they grind the clams and mussels down.  The shells of the clams and mussels are made of calcium carbonate.  Humans cannot each these shells as shells because human teeth aren’t made to grind down thick shells.



CaCo3 + chitin help make up the horseshoe crab’s shell.

(See earlier post for information on chitin.)

People complain that it is tough and hard if they step on one.  These two elements are the reason why.

One question I always ask the students who come is: what are your bones made out of? The sad fact is that the majority do not know.  They  know about the TV commercials telling them to drink milk for strong bones but they don’t know WHAT makes their bones strong.

Calcium is the link between all living creatures that have bones and shells.  Calcium is the fifth most abundant element on earth and has many variations (I’m not getting into more than basic chemistry here).  One of the variations that link us to the horseshoe crabs and all of the other shelled animals like oysters and lobsters is CaCO3, or calcium carbonate.

Calcium carbonate is a calcium compound.  We use it all the time and use products that contain it all the time like toothpaste, vitamins, almond milk, as a calcium supplement, and when we eat dark green vegetables like kale.

Calcium carbonate may have the ability to neutralize acid rain in river water and river ecosystems even though it is not soluble, or dissolves, in water.

CaCO3 is the reason we have fossils of horseshoe crabs going back 450 million years.  It is also the reason their shells are so strong and tough.  It is their home, their refuge, their protection.  CaCO3 is the reason they can travel hundreds of miles through the water and then make it to the shores to lay their eggs.

Calcium carbonate is the reason we get to see them now.