The 450-million-year-old crab saving humanity

Blue blood: Every year, scientists bleed half a million horseshoe crabs to extract lysate. © Timothy Fadek

Does it all come back to nature? A substance key to making a Covid-19 vaccine is only found in horseshoe crabs. But conservationists are worried falling numbers will threaten ecosystems.

A horseshoe crab has probably saved your life. If you have ever had an injection, it will have been tested to make sure it is free from potentially deadly endotoxins. The test uses a rare substance only found in the milky blue blood of these prehistoric athropods. Now, as scientists race to find a Covid-19 vaccine, this life-saving creature is under threat.

Despite its name, the horseshoe crab is not actually a crab, but a marine relative of spiders and scorpions. But whilst its land-dwelling cousins evolved into 100,000 different species, this sea creature remained virtually unchanged for 450 million years.

It has survived several mass extinctions and has preserved an ancient biology that turns out to be essential for modern medicine.

But this great survivor now faces its biggest challenge yet: humans. Each spring, hundreds of thousands of horseshoe crabs clamber out of the Atlantic Ocean to lay their eggs on beaches in the United States. Technicians haul them off to laboratories, tap their blood, extract the precious lysate, and then return them to the sea.

However, research shows fewer and fewer are coming back. As many as 30% that are returned to the ocean are dying, and in Delaware Bay their numbers have declined dramatically from 1.24 million in 1990 to only 335,211 today.

So, in the end, does it all come back to nature?


Some say, no, we are becoming less dependent on nature. For over a hundred years, modern technology has been swapping natural materials for man-made alternatives.

Others say, yes, we are part of the natural world and should never forget our dependence on it. It is science fiction to imagine we can separate ourselves from the rest of nature. Instead, we need to better understand ecosystems and how to protect them.

You Decide

  1. Should we use horseshoe crab blood to make vaccines?


  1. Design your own man-made life form to solve one of the world’s biggest problems. Draw a picture of what it looks like and how it can help save the planet.

Some People Say...

“We are all together in this; we are all together in this single living ecosystem called planet Earth.”

Sylvia Earle, American marine biologist.

What do you think?

Q & A

What do we know?
Most agree that life on Earth is around 4.6 billion years old, during which time over five billion species have evolved – and over 99% of them are now extinct. Whilst all lifeforms interact with the natural world, at some point in our prehistory, humans began to control nature. Primitive tool use developed into increasingly more advanced technology and we began to see ourselves as separate from nature.
What do we not know?
Whether the total separation between humans and nature is achievable, or even desirable. Some believe modern technology is bringing about a man-made revolution that will free us from the limits of the natural world. Others argue that we ignore at our peril humanity’s dependence on nature. In the last 50 years, humanity has wiped out 60% of animal populations, and we don’t know whether we will survive the sixth extinction.

Word Watch

Horseshoe crab
Often referred to as “living fossils” because they have changed very little over the last 450 million years. Two-feet long with nine eyes, armoured shell and a spined tail, they are one of evolution’s strangest survival stories. Other prehistoric animals still alive today include the duck-billed platypus, the crocodile, and the cow shark.
These toxins are found in some bacteria, like E. coli and salmonella, and are very difficult to detect. Limulus amebocyte lysate, extracted from the horseshoe crab blood, reacts to these toxins allowing scientists to detect them in medicines and medical equipment.
Rare substance
Limulus amebocyte lysate (or LAL).
Invertebrate animals with an exoskeleton (skeleton on the outside that supports and protects an animal’s body), such as an insect, spider, or crustacean.
Belonging to water or the sea.
Mass extinctions
Scientists studying the fossil record have noted five major mass extinctions in the last 450 million years. The most recent event took place 66 million years ago and wiped out 75% of all species on Earth, including all flightless dinosaurs. The event was probably caused by a massive asteroid impact.
Precious lysate
At £48,000 per gallon, it is one of the most expensive liquids in the world. The most expensive is scorpion venom (over £30m per gallon), which is used to treat multiple sclerosis, inflammatory bowel disease, and rheumatoid arthritis.
Delaware Bay
An estuary outlet of the Delaware River on the northeast seaboard of the United States. The bay’s fresh water mixes for many miles with the salt water of the Atlantic Ocean.

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