Horseshoe crabs are not crabs, they are in the arthropod family and related to spiders and scorpions.
They have been on the planet for 445 million years and they’ve changed very little during that time.
The oldest land animals date to about 415 million years ago. Those early land residents were scorpions, spiders and insects; the horseshoe crab’s closest living relatives.
Horseshoe crab eggs. Image by:Piotr Naskrecki
The female can lay up to 80,000 eggs a season.
Shorebirds eat many of the eggs before they have a chance to hatch.
Their eggs are a main source of food for millions of migratory birds.
Image Rob J:citybirder.blogspot.com
After 4 to 30 days the larvae emerge.
Horseshoe crabs spend the first two years of their life close by to where they hatched. Then they will travel to deeper water.
They can not reproduce until they are 9 to 11 years old.
They can live up to 30 years.
They have baby blue blood.
They have copper in their blood (hemocyanin), not iron (hemoglobin).
Their blood protects them from infection. For this reason, their blood is capable of detecting toxins in medical applications.
A protein from horseshoe crab blood is under going tests as an antibiotic.
Females are 20-30 percent larger than males.
Their brain’s are doughnut-shaped and encircle the mouth.
They can regrow lost limbs.
Their shells are composed of chitin.
Having shells of chitin (think beetle or lobster shells) rather than of calcium carbonate (shells, eggshells) makes them able to tolerate low-oxygen water and ocean acidification.
Horseshoe crabs have 9 eyes and can see UV light. They are the oldest living animal with compound eyes.
© Jürgen Freund,www.jurgenfreund.com
They can swim upside down.
They love muddy water and eat worms and mollusks on the seafloor.
Seagulls will eat them if overturned on a beach. Loggerhead sea turtles eat adolescent and adult horseshoe crabs.
The largest population in the world show up in Delaware Bay during mating season.
Horseshoe crabs mating. Image by:Piotr Naskrecki
During the breeding season, horseshoe crabs head toward shallow coastal waters.
They do not venture toward shore when the surf is rough.
The male fertilizes the eggs after the female releases them in the sand close to the high tide water line. The male holds onto the back of the females shell while she lays the eggs. If there are less females than males, extra males will stay near a mating couple to help fertilize the eggs.
A male might hold onto a female for days during mating season.
Many millions of horseshoe crabs have been used by humans as fishing bait and for fertilizer. In Asia the are also eaten by humans.
When their numbers started to drop precipitously, the Atlantic States Marine Fisheries Commission set restrictions.
Never pick up a horseshoe crab by its telson (tail).
Each spring during breeding season about 10% of the horseshoe crab population dies when rough surf flips them onto their backs. The ‘Just Flip ’em’ campaign asks that you gently turn them onto their stomachs. Have no fear, they are gentle creatures. They do not bite. But we do.
PBS: Crash: A Tale of Two Species:pbs.org
New Jersey, South Carolina and Fire Island, NY. have moratoriums on harvesting. In Delaware harvesting is restricted to males only. – See more at: https://web.archive.org/web/20150915003723/https://www.inspirationgreen.com/horseshoe-crab-facts.html#sthash.NInZffKV.dpuf