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 declining 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. “When you think about it,” says conservationist Barbara Brummer, “your mind is boggled by the reliance that we have on this primitive creature.” Each spring, hundreds of thousands 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 return them to the sea.

However, research shows fewer and fewer are coming back. As many as 30% 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. Over-harvesting for fish bait and human activity on their spawning beaches have also affected numbers.

But so what? As long as there are enough to keep our drugs safe, human lives are surely more important than the humble crab?

Biologist Larry Niles disagrees. This isn’t just about crabs, he says. “It’s about keeping ecosystems productive.” The annual crab-egg bonanza in Delaware Bay supports fish, terrapins, and migratory birds, all of which are in decline. And the birds – red knots and ruddy turnstones – are the biggest concern. They refuel on horseshoe crab meat during their epic 9,000-mile migration from South America to the Arctic.

If the migratory birds die out, there will be knock-on effects in ecosystems on opposite sides of the planet. Conservationists fear we are already living through a man-made sixth extinction, which threatens life on Earth and our own survival.

So, it is essential we conserve these ancient animals – as well as find synthetic alternatives to naturally sourced medical substances. Some believe that advances in genetic engineering, synthetic biology, and nanotechnology are leading to a revolution in our relationship to nature. But, at the same time, biologists are scouring rainforests for undiscovered plants with medicinal properties.

Now, the disastrous impact of Covid-19 and the sacrifice of the horseshoe crab reminds us how dependent we still are on the natural world. Even in the sterile, hi-tech labs working on a Covid-19 vaccine, a prehistoric arachnid is saving lives.

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 substituting natural materials for man-made alternatives. From nylon and plastic to synthetic bacteria and nanomedicine. Within another hundred years, we will have left nature entirely behind – which will be good news for us, the planet, and the horseshoe crabs.

Others say, yes, we are part of the natural world and should never forget our dependence on it. The planet is one giant interconnected ecosystem that supports 8.7 million species and there are 10,000 different organisms alone in the human body. It is simply 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?
  2. Have humans separated themselves from the natural world?


  1. Design your own man-made lifeform 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.
  2. It takes 10 years for a juvenile horseshoe crab to reach adulthood and lay its eggs in Delaware Bay. Scientists know very little about where they go during those years. Write a story about the secret adventures of the horseshoe crab.

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?
It is generally agreed 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 in unprecedented ways. Primitive tool use developed into increasingly more advanced technology and we began to see ourselves as separate from nature.
What do we not know?
One main area of debate is whether the complete separation between humans and nature is achievable, or even desirable. Some believe modern technology is bringing about a synthetic revolution that will liberate 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 carapace 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.
Mass extinctions
Scientists studying the fossil record have documented 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.
The British scientist Jame Lovelock has proposed the idea that the entire planet is one self-regulating complex system. This controversial idea, known as the Gaia Hypothesis, has been influential for thinking about how small changes have big effects on the environment.
Sixth extinction
Humans have been described as a “global superpredator”, which has impacted ecosystems and caused widespread extinction since the end of the last Ice Age, 12,000 years ago.
Synthetic alternatives
A man-made alternative substance has been developed, but has not been approved for use in the US.
Synthetic biology
In 2010, scientists created the first man-made organism (a cattle bacterium) and are working on designing synthetic lifeforms that can detect poison, clear up oil spills, kill cancer cells, and build electric circuits.
As digital technology and robots get smaller and smaller, scientists are designing electronic tattoos to monitor patients, injectable sensors, and nanobots to help with post-surgery recovery.

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