What makes crabs blue

The blue crab is so named because of its sapphire-tinted claws. Its shell, or carapace, is actually a mottled brownish color, and mature females have red highlights on the tips of their pincers. Prized by humans for their sweet, tender meat, these wide-ranging, ten-legged crustaceans are among the most heavily harvested creatures on the planet.

Their scientific name, Callinectes sapidus , means "savory beautiful swimmer. Blue crabs are found in brackish coastal lagoons and estuaries from Nova Scotia, through the Gulf of Mexico, and as far south as Uruguay. Close relatives of the shrimp and lobster, these bottom-dwelling omnivores have a prickly disposition and are quick to use their sharp front pincers.

Large males can reach 9 inches in shell width. They feed on almost anything they can get hold of, including mussels, snails, fish, plants, and even carrion and smaller blue crabs.

They are also excellent swimmers, with specially adapted hind appendages shaped like paddles. Blue crabs are extremely sensitive to environmental and habitat changes, and many populations, particularly in the Chesapeake Bay in the eastern United States, have experienced severe declines. Blue crabs also play a key role in managing the populations of the animals they prey on, and constant overharvesting has had wide-ranging negative effects on the ecosystems they inhabit. For this reason, comprehensive management schemes are in place in several parts of the blue crab's range.

All rights reserved. Common Name: Blue Crab. Scientific Name: Callinectes sapidus. Type: Invertebrates. Diet: Omnivore. Group Name: Cast. Size: 4 inches long; 9 inches wide. Weight: 1 to 2 pounds. Size relative to a teacup:. Not evaluated. Least Concern Extinct. Current Population Trend: Unknown. This photo was submitted to Your Shot, our photo community on Instagram. Follow us on Instagram at natgeoyourshot or visit us at natgeo.

Share Tweet Email. Go Further. These delightfully colorful crabs take up residence in waters from Nova Scotia to the Gulf of Mexico, and even further south along the coasts of Argentina and Uruguay.

Nowhere is the crab more iconic, though, than the Chesapeake Bay. In the waters off Maryland and Virginia, the blue crab population thrives in the brackish estuaries and salt marshes. Stowaway blue crabs on ship ballasts have even showed up in the Mediterranean. There, however, the crab is invasive. It was first seen off Egyptian waters in the s, but reports of blue crab sightings in Italy, Israel, Greece, and Turkey have been made, too.

As such, many coastal communities have found ways to use the foreign crustaceans as a source of food and income.

Blue crab mating season stretches from May to October. Once females reach sexual maturity, they mate with a male only once. Males will mate with multiple females during their lifespan. This mass, or sponge, can contain as many as 2 million eggs. There, the blue crab larvae, or zoea, molt over 25 times and grow before the maturing crabs make their way back to the estuaries and salt marshes to start their own reproductive process.

They eat clams, mussels, snails, dead fish, plants, and more.