ما هي الحيوانات التي تعيش في أعماق البحار؟
12 من أقدم أنواع الكانات البحرية التي لا تزال موجودة حتى يومنا هذا
والأكثر إثارة للإعجاب هو قرش أعماق البحار جرينلاند المراوغ والذي يعد أحد أقدم الأنواع الحية. يُعتقد أنه يمكن أن يصل عمره إلى أكثر من 500 عام!
May 14, 2023
سرطان البحر حدوة الحصان
تمامًا مثل سرطان البحر الحصان ، ظل <anchor>سرطان البحر حدوة الحصان</anchor> على حاله طوال فترة وجوده – والتي استمرت 450 مليون عام. هم في الواقع أنها أقرب إلى العناكب والعقارب من سرطان البحر ، وحتى أنهم مثل أقربائهم من تلك الفصائل لهم وهج تحت ضوء الأشعة فوق البنفسجية!
10 Incredible Horseshoe Crab Facts | Smithsonian's National Zoo and Conservation Biology Institute
## Header Links

Today's hours: 8 a.m. to 6 p.m. (last entry 5 p.m.)

## Mega menu

## Animals Global Nav Links

See the Smithsonian's National Zoo's Asian elephants — Spike, Bozie, Kamala, Swarna, Maharani, Trong Nhi and Nhi Linh — live on camera.

## Support Global Nav Links

Image: Red panda Chris-Anne eats bamboo in her outdoor habitat. 

Now more than ever, we need your support. Make a donation to the Smithsonian's National Zoo and Conservation Biology Institute today!

## Membership Global Nav Links

Image: A mother and her child look at an underwater exhibit with a pinniped (sea lion or seal) swimming in the water

Members are our strongest champions of animal conservation and wildlife research. When you become a member, you also receive exclusive benefits, like special opportunities to meet animals, discounts at Zoo stores and more.

## Education Global Nav Links

Image: An educator wearing a protective face covering talks to students via video on a phone and points out leaves and trees in the Amazonia exhibit

Find and register for free programs and webinars.

## Conservation Global Nav Links

Search

June 03, 2022

# 10 Incredible Horseshoe Crab Facts

An aerial photo of two horseshoe crabs on the sand in shallow tidal waters

The ocean has many unusual inhabitants, but few are as strange and ancient as the horseshoe crab. Get to know these living armored tanks that have roamed coastal seas for millennia.

### 1. Horseshoe crabs predate the dinosaurs.

Just how old are horseshoe crabs? Scientists have discovered fossils of their ancient ancestors that lived 445 million years ago. Dinosaurs first appeared about 200 million years later, during the Mesozoic era.

Horseshoe crabs went on to survive the extinction event that wiped dinosaurs from the planet 66 million years ago. Four species survive today — one found in the Atlantic coastal waters of North America and the Gulf of Mexico and three found in Asia’s coastal waters.

Horseshoe crabs have not evolved much in the past 200 million years, which is why they are often called “living fossils.”

### 2. Horseshoe crab blood is blue.

Human blood is red because our hemoglobin — the protein in red blood cells that transports oxygen around the body — contains iron. Horseshoe crabs have a different oxygen-carrying protein, called hemocyanin. Hemocyanin has copper rather than iron, which gives horseshoe crab blood its bright blue color.

Image: A horseshoe crab on a sandy beach at sunset

### 3. They have six pairs of legs but only five are for walking.

Horseshoe crabs walk on 10 legs and use their last pair, called the chelicera, to move food into their mouths. They eat worms, algae, clams, and other small prey that they root out in the sediment on the ocean floor. Horseshoe crabs have no jaws, so they crush their meals between their legs before eating.

### 4. One horseshoe crab can lay about 4,000 eggs.

Atlantic horseshoe crabs are found from Florida to Northern Maine and in the Yucatán peninsula. The largest populations live in the Delaware Bay. From May to early June, they swarm the beaches to breed and lay eggs. They arrive in huge numbers during high tides that coincide with the full moon or new moon. Females dig nests in the sand and bury a cluster of about 4,000 tiny, blue-green eggs. They can lay about 20 egg clusters each year!

Image: Sand covered in tiny, blue-green horseshoe crab eggs

### 5. Horseshoe crab babies look just like adults — but with translucent shells.

It takes two to four weeks for horseshoe crab eggs to hatch. Tiny crabs emerge, smaller than the eraser on a No. 2 pencil and with nearly see-through shells. The baby horseshoe crabs find shallow, sheltered waters to live in. They molt several times in their first year, shedding their old shells to reveal new shells underneath. Their shells darken as they age. The crabs continue to molt, but with less frequency, as they grow older.

### 6. Many shorebirds can’t survive without horseshoe crabs.

Thousands of shorebirds descend on the Delaware Bay in May to feast on horseshoe crab eggs. Red knots, ruddy turnstones and sanderlings and other species rely on the fat- and protein-packed eggs to power their long flights. For red knots, this important stopover is the last chance to fuel up before the final leg of an epic 9,300-mile migration from South America to the Arctic.

But fishers use horseshoe crabs as bait to catch eels and whelk (sea snails), and crab populations are getting smaller. In some states, it’s illegal to catch horseshoe crabs. If harvests continue, the crabs could disappear — along with the shorebirds that rely on them.

Image: Shorebirds flying over a sandy shoreline in the Delaware Bay

### 7. They are not true crabs.

Horseshoe crabs are arthropods, but they are more closely related to scorpions and spiders than crustaceans. They are the only living members of the Xiphosura order.

### 8. You may be alive today thanks to a horseshoe crab.

Horseshoe crab blood contains a unique enzyme called limulus amebocyte lysate, or LAL. It causes the blood to coagulate when exposed to bacterial endotoxins, which can be deadly. Biomedical companies use LAL to test medicines, vaccines, implants, and more for endotoxins. It’s how they ensure medical equipment is safe for people.

Unfortunately, many horseshoe crabs die in the process of collecting their blood. Scientists are exploring synthetic alternatives to LAL. Finding a replacement will help ensure a future for horseshoe crabs and shorebirds.

Image: Horseshoe crabs pile on top of each other on a sandy shore near a breaking wave

### 9. A horseshoe crab’s pointed tail is not for self-defense.

Horseshoe crabs are easily jostled by ocean currents and waves — and each other. When a crab gets stuck upside-down, it uses its tail, called a telson, to flip over! Horseshoe crabs can also use their telson as a rudder to help steer as they swim upside down.

Luckily, horseshoe crabs are not powerless against predators, like sea turtles, sharks and gulls. Their tough shells are good shields.

### 10. They glow under UV light.

Like scorpions, horseshoe crabs exhibit fluorescence under ultraviolet light (or blacklight). Scientists don’t know why horseshoe crabs fluoresce, but younger crabs with lighter shells glow brighter than adults.

## Continue Exploring

August 20, 2024

On the wings of last year’s award-winning baby boom, our Bird House team recently welcomed 27 chicks among seven duck and songbird species! Meet them in this update.

March 25, 2024

Three chirps for our Bird House team! In recognition of their efforts to breed and care for North American songbirds, they received a Plume Award from the Association of Zoos and Aquariums’ Avian Scientific Advisory Group.

February 18, 2024

Our Bird House team is celebrating the arrival of a ruddy quail dove squab—the first of its species to hatch at the Zoo!

### Contact Us

### Address

Smithsonian's National Zoo & Conservation Biology Institute

3001 Connecticut Ave., NW

Washington, DC 20008

## About the Zoo

## Careers

## News & Media

## Footer Donate

## Shop

## Follow us on social media

## Sign Up for Emails

EmailSign up!

## Footer - SI logo, privacy, terms