--- title: "Atlantic Horseshoe Crab (Limulus polyphemus) | AnimalTracks.wiki" description: "A blue-blooded cousin of spiders and scorpions, with ten eyes and blood that clots when it meets certain bacteria." image: "https://animaltracks.wiki/images/animals/atlantic-horseshoe-crab-1.webp" published: "2026-09-29" updated: "2026-09-29" --- # Atlantic Horseshoe Crab (*Limulus polyphemus*) > **Status**: Checked against 5 sources, listed under Sources below. > **Tagline**: A blue-blooded cousin of spiders and scorpions, with ten eyes and blood that clots when it meets certain bacteria. > **Soundtrack Vibe**: Neo-Classical & Baroque Chamber // Philip Glass, "Glassworks: Opening" > **Soundtrack Links**: [Spotify](https://open.spotify.com/track/2XYEu7Deyz20WeL6Py3XLc) > **Vibe Match**: In the spring, crabs come ashore during the new and full moons to spawn. Glass builds Opening from one rolling piano figure that keeps coming back around, like a tide. ## Biological Superpowers & Stats - **Taxonomy**: *Limulus polyphemus* - **Danger Level**: Low - **Conservation Status**: Vulnerable ([IUCN Red List](https://doi.org/10.2305/iucn.uk.2016-1.rlts.t11987a80159830.en)) - **Superpower**: Blue blood that clots when it meets certain bacteria, which labs use to test medicines and medical devices for endotoxins. - **Habitat**: Shallow coastal waters on sandy or muddy bottoms, on the Atlantic coast from Maine to the Yucatan Peninsula - **Diet**: Worms, bivalves, and other small bottom-dwelling organisms - **Tags**: invertebrate, living-fossil, benthic, ocean, carnivore ## Natural History & Behavior ## Blue Blood That Catches Germs Horseshoe crab blood is straw-colored and turns blue when it meets high levels of oxygen. The blue comes from hemocyanin, a copper-rich protein, where our red blood uses iron-based hemoglobin. The blood carries cells called amebocytes, which make it clot when it meets potentially harmful gram-negative bacteria, a type of germ that carries endotoxins in its cell walls. Labs use that reaction in the Limulus Amebocyte Lysate (LAL) test, which checks pharmaceuticals and medical devices for potentially deadly endotoxins. > **Blood donors without a choice** Each year, the medical industry catches around half a million horseshoe crabs just to harvest their blood. A review of the practice reports that mortality after harvest ranges from 10 to 30%. A synthetic alternative is slowly replacing it. ## A Cousin of Spiders Despite the name, Atlantic horseshoe crabs are more closely related to spiders and scorpions than to true crabs. Their body has three parts: the prosoma (the front shell shaped like a horseshoe), the opisthosoma (the back section) and the telson, the tail. The spiky tail is usually mistaken for a weapon, but it is harmless. It helps the crab flip itself over if waves on the beach turn it over. This design has stayed relatively unchanged in appearance for 350 million years. Adults are up to 2 feet long including the tail and weigh 3 to 4 pounds. The largest crabs are found on the Georgia coast, where mature females grow to about 11 pounds (4.8 kg). Males are typically 25 to 30% smaller than females. In the wild they live 20 to 40 years. They have ten eyes, and the two large compound eyes on the sides are mainly used to locate a mate. Their rods and cones, the cells that detect light, are the largest of any known animal. ## Life on the Sandy Bottom The species lives in shallow coastal waters on sandy or muddy bottoms, on the Atlantic coast from Maine to the Yucatan Peninsula. It eats worms, bivalves and other small bottom-dwelling organisms. ## The Moonlight Egg Rush In the spring, crabs come ashore during the new and full moons to spawn. A female drags a male clasped to her shell, and she can lay 100,000 eggs over a few nights. The eggs are a critical food source for the red knot, a migratory bird with one of the longest known migration ranges, 9,000 miles. ## Frequently Asked Questions ### Is a horseshoe crab dangerous to touch? No. It looks prehistoric and menacing, with many legs and a tail that looks like a stinger, but the U.S. Fish & Wildlife Service says it is completely harmless. *(Source: [U.S. Fish & Wildlife Service]())* ### How many eyes does a horseshoe crab have? Ten. Two large compound eyes sit on the sides of the shell, and the National Park Service says their main job is finding a mate. Eight other light-sensitive eyes are scattered over the body, shell and even the tail, and they help the crab stay oriented. *(Source: [National Park Service]())* ### Does bleeding kill horseshoe crabs? Sometimes. A review reports a 30% death rate after bleeding female horseshoe crabs and 8% after bleeding males, and it notes that reported figures leave out later trauma once the crabs are returned to the ocean. *(Source: [Krisfalusi-Gannon et al. 2018]())* ## Sources 1. [Atlantic Horseshoe Crab. Marine Biological Laboratory, University of Chicago.]() 2. [Atlantic Horseshoe Crab (Limulus polyphemus). U.S. Fish & Wildlife Service.]() 3. [Northeast Coastal and Barrier Network Species Spotlight: Atlantic Horseshoe Crab. National Park Service.]() 4. [Krisfalusi-Gannon et al. (2018). The Role of Horseshoe Crabs in the Biomedical Industry and Recent Trends Impacting Species Sustainability. Frontiers in Marine Science.]() 5. [Smith et al. (2016). Limulus polyphemus. The IUCN Red List of Threatened Species 2016: e.T11987A80159830.]() *Published September 29, 2026. Last updated September 29, 2026.* ```json { "@context": "https://schema.org", "@graph": [ { "@type": "Article", "@id": "https://animaltracks.wiki/animals/atlantic-horseshoe-crab/#article", "isPartOf": { "@id": "https://animaltracks.wiki/#website" }, "headline": "Atlantic Horseshoe Crab (Limulus polyphemus) | AnimalTracks.wiki", "description": "A blue-blooded cousin of spiders and scorpions, with ten eyes and blood that clots when it meets certain bacteria.", "image": [ "https://animaltracks.wiki/images/animals/atlantic-horseshoe-crab-1.webp" ], "datePublished": "2026-09-29", "dateModified": "2026-09-29", "author": [ { "@type": "Organization", "name": "AnimalTracks.wiki Editorial Team", "url": "https://animaltracks.wiki" } ], "publisher": { "@type": "Organization", "@id": "https://animaltracks.wiki/#organization", "name": "AnimalTracks.wiki", "url": "https://animaltracks.wiki", "logo": { "@type": "ImageObject", "url": "https://animaltracks.wiki/icon-512.png" } }, "mainEntityOfPage": "https://animaltracks.wiki/animals/atlantic-horseshoe-crab/", "citation": [ { "@type": "CreativeWork", "name": "Atlantic Horseshoe Crab", "url": "https://www.mbl.edu/research/research-organisms/atlantic-horseshoe-crab", "publisher": { "@type": "Organization", "name": "Marine Biological Laboratory, University of Chicago" } }, { "@type": "CreativeWork", "name": "Atlantic Horseshoe Crab (Limulus polyphemus)", "url": "https://www.fws.gov/species/atlantic-horseshoe-crab-limulus-polyphemus", "publisher": { "@type": "Organization", "name": "U.S. Fish & Wildlife Service" } }, { "@type": "CreativeWork", "name": "Northeast Coastal and Barrier Network Species Spotlight: Atlantic Horseshoe Crab", "url": "https://www.nps.gov/articles/ncbn-species-spotlight-atlantic-horseshoe-crab.htm", "publisher": { "@type": "Organization", "name": "National Park Service" } }, { "@type": "ScholarlyArticle", "name": "The Role of Horseshoe Crabs in the Biomedical Industry and Recent Trends Impacting Species Sustainability", "url": "https://doi.org/10.3389/fmars.2018.00185", "author": "Krisfalusi-Gannon et al.", "datePublished": "2018", "isPartOf": { "@type": "Periodical", "name": "Frontiers in Marine Science" }, "identifier": "doi:10.3389/fmars.2018.00185" }, { "@type": "ScholarlyArticle", "name": "Limulus polyphemus. The IUCN Red List of Threatened Species 2016: e.T11987A80159830", "url": "https://doi.org/10.2305/iucn.uk.2016-1.rlts.t11987a80159830.en", "author": "Smith et al.", "datePublished": "2016", "isPartOf": { "@type": "Periodical", "name": "The IUCN Red List of Threatened Species" }, "identifier": "doi:10.2305/iucn.uk.2016-1.rlts.t11987a80159830.en" } ], "about": { "@type": "Taxon", "name": "Atlantic Horseshoe Crab", "scientificName": "Limulus polyphemus", "description": "Blue blood that clots when it meets certain bacteria, which labs use to test medicines and medical devices for endotoxins." } }, { "@type": "FAQPage", "@id": "https://animaltracks.wiki/animals/atlantic-horseshoe-crab/#faq", "mainEntity": [ { "@type": "Question", "name": "Is a horseshoe crab dangerous to touch?", "acceptedAnswer": { "@type": "Answer", "text": "No. It looks prehistoric and menacing, with many legs and a tail that looks like a stinger, but the U.S. Fish & Wildlife Service says it is completely harmless.", "citation": { "@type": "CreativeWork", "name": "Atlantic Horseshoe Crab (Limulus polyphemus)", "url": "https://www.fws.gov/species/atlantic-horseshoe-crab-limulus-polyphemus", "publisher": { "@type": "Organization", "name": "U.S. Fish & Wildlife Service" } } } }, { "@type": "Question", "name": "How many eyes does a horseshoe crab have?", "acceptedAnswer": { "@type": "Answer", "text": "Ten. Two large compound eyes sit on the sides of the shell, and the National Park Service says their main job is finding a mate. Eight other light-sensitive eyes are scattered over the body, shell and even the tail, and they help the crab stay oriented.", "citation": { "@type": "CreativeWork", "name": "Northeast Coastal and Barrier Network Species Spotlight: Atlantic Horseshoe Crab", "url": "https://www.nps.gov/articles/ncbn-species-spotlight-atlantic-horseshoe-crab.htm", "publisher": { "@type": "Organization", "name": "National Park Service" } } } }, { "@type": "Question", "name": "Does bleeding kill horseshoe crabs?", "acceptedAnswer": { "@type": "Answer", "text": "Sometimes. A review reports a 30% death rate after bleeding female horseshoe crabs and 8% after bleeding males, and it notes that reported figures leave out later trauma once the crabs are returned to the ocean.", "citation": { "@type": "ScholarlyArticle", "name": "The Role of Horseshoe Crabs in the Biomedical Industry and Recent Trends Impacting Species Sustainability", "url": "https://doi.org/10.3389/fmars.2018.00185", "author": "Krisfalusi-Gannon et al.", "datePublished": "2018", "isPartOf": { "@type": "Periodical", "name": "Frontiers in Marine Science" }, "identifier": "doi:10.3389/fmars.2018.00185" } } } ] }, { "@type": "MusicRecording", "name": "Glassworks: Opening", "byArtist": { "@type": "MusicGroup", "name": "Philip Glass" }, "genre": "Neo-Classical & Baroque Chamber", "url": "https://open.spotify.com/track/2XYEu7Deyz20WeL6Py3XLc" } ] } ```