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Horseshoe Crab


Horseshoe “crabs” (HSC) are marine arthropods and are sometimes referred to as “living fossils”. A funny fact is, that even though they are called Horseshoe crabs, they are more related to spiders, ticks and scorpions than they are to actual crabs. Their ancestors have been on this planet for around 400 million years and they survived several mass extinctions.

In total, there are four living species of horseshoe crabs. One inhabits the Eastern and Gulf coasts of North America: Limulus polyphemus, while the other three are found in Southeast Asia: Tachypleus gigas, Tachypleus  tridentatus and Carcinoscorpius  rotundicauda.

The blue blood

Horseshoe crab’s blood has a special blue color due to the presence of hemocyanin that transport oxygen throughout the horseshoe crab’s body.

The critical component of the reagents used in endotoxin tests is derived from cells (amebocytes) found in the blue blood of the horseshoe crab, Limulus polyphemus. The lysate of these amebocyte cells, Lymulus Amebocyte Lysate or LAL, contains the proteins of the blood clotting mechanism. This clotting mechanism reacts to antigens found negative bacteria known as lipopolysaccharides (LPS) or endotoxins. In vivo, the formed clot isolates invasive bacteria, and protects the crab from infection. The blood also begins a healing process similar to ours where we form a clot, a scab, and eventually wounds heal.

The LAL reagents are prepared from blood obtained by collecting adult horseshoe crabs and extracting a portion of their blood. The process is very similar to when people donate blood. The crabs are checked for good health, placed in a very clean laboratory, where a small portion of the blood is collected carefully with a sterile needle.

The LAL test is the most sensitive, accurate and cost effective test on the market today to detect contaminating endotoxins. This test was first licensed by the FDA in the 1970’s, and is still the gold standard. It can detect endotoxin in the parts per billion. That’s like finding a grain of sand in an Olympic swimming pool.

The blood coagulation process in the LAL reagent, activated by endotoxins, can be monitored visually in the laboratory using the gel clot method or can be recorded photometrically using a turbidimetric or chromogenic method.

Life history

Did you know?

During the breeding season, adult horseshoe crabs migrate to beach areas to spawn. They prefer sandy beaches within bays and coves that are protected from the force of the oceanic waves. Spawning time occurs at high tide and peaks around full and new moon. The males will arrive first at the breading beach, awaiting the females.

A female lays about 90 000 eggs per year in different clusters, each of around 4 000 eggs. The eggs incubate in sand for two to four weeks. The young horseshoe crabs undergo ecdysis six times during their first year of life, each time growing about 25% in linear dimensions. After the first year, horseshoe crabs will moult only once a year until they reach sexual maturity. They reach maturity around nine to eleven years old and have a life expectancy of at least fifteen to eighteen years.

The juveniles stay in nearshore areas. As they grow older, they move away gradually from their shallow natal area into deeper estuarine waters. The adults remain offshore for the duration of the life cycle, returning to the beach to breed.

  • They avoid bleeding crabs more than once a year. Therefore crabs are marked with a mark which is not harmful to the crab.
  • Horseshoe crabs use their tail, called telson, primarily to flip themselves upright if they are overturned.


The Horseshoe Crab Sustainability Project of Associates of Cape Cod, Inc.

Our partner, Associates of Cape Cod, Inc. (ACC), is pleased to announce an exciting new initiative aimed at complementing their 45 year history of horseshoe crab conservation. ACC introduced a Horseshoe Crab Sustainability Project that will help ensure a stable supply of horseshoe crabs now and for future generations to come. Working with local regulators, having received a class 1, type 4 aquaculture permit and utilizing a patent pending process, ACC collects HSC eggs, fertilizes, grows and strategically releases horseshoe crabs back into their natural environment. This program only utilizes eggs collected from bait crabs that are sacrificed for the eel, conch and whelk fisheries, extending their genetic legacy for generations to come.  See the videos of ACC for more information about their project.

Horseshoe Crab Conservation And The Truth About The BioMedical Impact On The Population -FEB 2020

There has been a lot of misinformation regarding the impact that the biomedical industry has on horseshoe crabs ranging from population numbers to the cost of their blue blood. This video provides current data about horseshoe crab populations, answers many frequently asked questions about this wondering creature and introduces you to a new horseshoe crab sustainability initiative from Associates of Cape Cod, Inc.

Red Knot Safe

Horseshoe crab eggs play an important role in the food web for migrating shorebirds. Therefore the female crabs from the Delaware bay region are not used to manufacture Lysate by ACC. The Lysate is “Red Knot Safe™” in order to sustain the Red Knots. A sufficient supply of horseshoe crab eggs is essential for Red Knots to have sufficient fuel to complete the journey north to the Arctic. For more information visit the “Red Knot Safe” website:

ACC’s BET White Papers:

Concernend about the horseshoe Crab?

Keep your method but make a change with the First Recombinant LAL Cascade Reagent: PyroSmart NextGen™.