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.