Honing in on the Horseshoe Crab

Horseshoe Crab - moult (shedded shell/exoskeleton)

Horseshoe crabs are prehistoric animals that existed on earth well before the dinosaurs. They have 10 legs and a hard exoskeleton (shell), and while they look like ancient crabs, they are actually more closely related to spiders and scorpions. The ‘horseshoe’ in its name actually comes from the shape of its head: U-shaped like a horse’s shoe.

Horseshoe crabs moult (shed) their shells about 6 times before they reach full adult size. Female horseshoe crabs are 1/3 bigger than males. These creatures have a long (venom-free) sharp tail that it uses to flip itself over if necessary. We have at least 2 species of horseshoe crabs in Johor, namely the Coastal Horseshoe Crab (Tachypleus gigas) and the Mangrove Horseshoe Crab (Carcinoscorpius rotundicauda).

Studies of these species show that their populations are in decline because of habitat damage and human consumption. A popular ‘exotic food’ in Malaysia, people catch it to eat its eggs, which means they are not able to repopulate before being caught. It is also taken by researchers (in large numbers!) to study its blue blood, which has a substance vital to the study of cancer cures. Horseshoe crabs can live until they are 30 years old and are only able to reproduce at 9 to 12 years. This means that overharvesting causes great damage to their continued existence.

Join Kelab Alami (kelabalami.weebly.com) on a mangrove or seagrass walk where you might be able to meet live horseshoe crabs in our shallows.