We Ain't Nothing but Arthropods!

 
Life Cycle/Reproduction 

 
Egg/Larvae Stage

 
Horseshoe crab eggs are buried higher up on sandy beaches in nests made by the female horseshoes. Temperatures vary here in the moist sand.  Each nest normally contain approximately 4,000 eggs!  An egg's size can be compared to a pinhead.  Once the egg breaks due to either age, hatching, or sand abrasion, the larvae will emerge! 

Horseshoe Crab eggs.
Photo by Greg Breese, USFWS

  

Juvenile

In order for arthropods to grow they need to molt.  Approximately 20 days after the egg hatched, the larvae will molt for the first time.  At a young age the horseshoe crab will molt many times throughout the first year of its life. As the crab ages it will molt about once a year.  During this stage of its life, it spends the first couple years in the intertidal flats.  As it gets closer to the adult stage it will move out to deeper waters.

Above: Two year old horseshoe crabs raised in Maryland classrooms.
Below: A picture of a male and female spawning.
 

Adult/Spawning Stage

 
When the horseshoe crab reaches the adult stage and sexual maturity, it moves back toward the sandy beaches.  It then begins its annual spawning migration.  By the time spawning season starts, the female horseshoe crab will have produced approximately 80,000 eggs!  When the horseshoe crabs leave the deep end for the shore, the males actually walk along the beaches, almost like they are patrolling, patiently waiting for the females.  When the females arrive, they gives off pheromones which is a chemical that the males can detect.  Once detected the males basically attend the females to the beach.  Many times a single female horseshoe crab will get surrounded by multiple males, typically around five or six.  After the nest is made and one clutch (~4,000 eggs) is laid by the female, the males grasp onto the back of the female then it lays its sperm onto the eggs.  Each spawning season a female will lay about 20 clusters.  This spawning process is repeated every year until the death of the horseshoe crab.

Atlantic Horseshoe Crab Life Cycle

This lifecycle I created myself referencing from http://www.horseshoecrab.org/

 

Mortality

 
There are multiple causes for the death of horseshoe crabs.  Beach stranding, diseases, and predation fall under the natural death category.  The bait fishing industry is another major cause of death.  Approximately 2.7 million crabs are killed due to harvesting them for eel and conch bait. The last major cause of death is due to our own medicinal purposes.  Between 20-40 thousand horseshoe crabs die due to drawing too much of their blood.  To learn more about harvesting horseshoe crabs visit http://dnr.maryland.gov/education/horseshoecrab/.

 

To learn about the horseshoe crab's interactions with other organisms click here!

To go back to the Nutrition page click here.

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