Blue crab Facts for Kids
Callinectes sapidus · kal-ih-NEK-teez SAP-ih-dus
A crab with paddle-shaped back legs that make it a great swimmer.
- 🏃 speed: not yet checked
- ⚖️ 5.3 oz150 g1
- 📏 9.1 in23 cm1 long
- 🎂 3 to 4 years3 to 4 years1
- 🍽️ plants and animals
- Not on the Red List (Not assessed)
The blue crab has a hard shell and two strong claws. Its back legs are flat like paddles, so it can swim. It runs sideways on the others.
A blue crab walks sideways on pointy legs, and its last pair are flat paddles for swimming. Like a lobster, it grows by climbing out of its old shell, and it is soft until the new shell hardens. Grown-up males have bright blue claws, and females have claws with red tips.
Blue crabs live in bays and river mouths, where fresh river water mixes with salty sea water. Their scientific name, Callinectes sapidus, starts with a word that means beautiful swimmer. Baby blue crabs drift in the sea and look nothing like their parents, then settle into grassy beds and marshes that hide them while they grow. Crabs are food for many animals, and fishers catch them in traps, so people protect marshes and seagrass and set limits on how many crabs may be caught.
How big is a blue crab?
Blue crab in numbers
| Length | 9.1 in23 cm1across the shell, up to |
|---|---|
| Height at the shoulder | no checked number yet |
| Weight | 5.3 oz150 g1at maturity, about |
| Top speed | no checked number yet |
| How long it lives | 3 to 4 years3 to 4 years1 |
| What it eats | clams, snails, small fish and plants |
| Where it lives | bays, river mouths and shallow coasts along the Atlantic coast of North America, including Chesapeake Bay, and the Gulf of Mexico |
| What kind | Bugs and other animals without backbones |
| Is it in danger? | Not on the Red List (Not assessed) |
A number we couldn’t find on a page we trust says so, instead of guessing.
Wow!
- Its scientific name starts with a word that means beautiful swimmer.
- Males have bright blue claws, and females have claws with red tips.
- A baby blue crab looks nothing like a grown-up and drifts in the sea.
Compare the blue crab
Friends and neighbours
American lobster
West Indian manatee
Green sea turtleThree questions
Books about the blue crab, free at the library
Ask a grown-up to tap the button: it shows where to borrow a book about the blue crab for free.
Where these numbers come from
- NOAA Fisheries, checked 30 October 2026.
- Wikidata, Blue crab (Q844839), checked 30 October 2026.