How well do you know the horseshoe crab?
The Horseshoe Crab is not a Crab.
Horseshoe crabs are arthropods, but they are not in the Crustacean class like crabs. Instead, they are in their own class called Merostomata and are actually more closely related to spiders and scorpions. No need to worry though; horseshoe crabs cannot bite or sting.
Horseshoe Crabs are a Sought-after Menu Item for Some Species.
Juvenile and adult horseshoe crabs do have predators. The list includes gulls, loggerhead sea turtles, alligators, and sharks. The eggs and larvae are eaten by many species of birds, fish, and turtles.
Reproduction is Difficult and Dangerous Work.
Females will lay as many as 80,000 to 100,000 eggs during one breeding season. The female will come onto the beach with the high tide to spawn, with at least one eager male attached to her. She then digs about six inches into the sand and deposits 4,000 to 5,000 tiny green eggs at once! Still attached, the males fertilize these tiny eggs after they are deposited, and then get a free tow back to the water by the female crab. Females will repeat this trip up to five times over the course of a month.
Horseshoe Crab Life is Hard!
Females lay tens of thousands of eggs in one season for a reason. Out of every 10,000 eggs, only six will hatch. Things don’t get any easier at this point – for every one hundred thousand larvae swimming along the mudflats, only about three will survive their first year. The lucky ones can live as long as 20-30 years.
Horseshoe Crabs Have Some Buff Bods!
Horseshoe crabs have over 750 individual muscles that make up their bodies; humans only have around 650.
Female Horseshoe Crabs Outweigh the Males.
Female horseshoe crabs are BIG – sometimes twice as large as the many suitors that will swarm around her during spawning. Males differ in other ways too. Males have a modified first set of appendages that look like boxing gloves and they have a concave shape to their shells that allows them to rest on the female more easily during spawning.
And Finally, These Little Critters are Big Heroes!
The horseshoe crab should be revered for its contribution to human health.
Not only has the horseshoe crab allowed medical researchers to gain a better understanding of human vision (which was so groundbreaking it led to a Nobel Prize in the 1930s), but they have directly impacted most everybody that is alive today. Horseshoe crab blood cells, called amoebocytes, have the ability to find and form clots around bacteria that would otherwise cause infection in the horseshoe crab. A solution called Limulus amoebocyte lysate (LAL) is produced from the blood cells. LAL is then used to test for the presence of gram negative bacteria on injectable drugs, vaccines, and implantable devices we use in human and animal medicine. About 500,000-600,000 crabs are harvested each year to support this use, each one having about one-third of their blood removed. Crabs are returned to the water and many survive, but many as 10-15% will not. Horseshoe crabs have been a critically important part of modern medicine, but there is now a synthetic replacement. If adopted by the Federal Drug Administration, it could end the need to bleed horseshoe crabs.
For an update on synthetic LAL see this recent post: Saving Horseshoe Crabs…one company at a time
Want to learn more about these incredible creatures? Visit horseshoecrab.org or pick up a copy of Horseshoe Crab – Biography of a Survivor by Anthony D. Fredericks.
