“Rusty” Maryland Blue Crabs: Signs of Natures Perfection

White Belly (Left), Rusty Bottom (Right)

Have you ever wondered why your blue crabs (callinectes sapidus) have that "rusty" look? Or perhaps they were bright white underneath? Well, blue crabs have different shell coloring for a reason. All of those colors are related to their molting cycles. A crab that is bright white underneath, is an indicator of the crab having gone through a recent shedding of their old shell.

Additionally, environmental factors such as water temperature, salinity levels, and food availability can influence the molting frequency and “rust” appearance of blue crabs. Before we get into what a “rusty” crab is, let's discuss what a molting cycle of the blue crab is...

From Pre-Molt to Post-Molt: The Life Cycle of Blue Crabs

A molt cycle is when a crab detaches itself from the old shell, forms a new soft exterior, backs itself out of the old shell, and waits for it's new shell to harden. This is a three stage process. First is the pre-molt (or peeler stage), second is the molting (or busting stage), and then finally the post molt (or soft shell stage). Male blue crabs typically go through 21-23 molting cycles in their life span!

White Belly Blue Crab (Left), Rusty Bottom Blue Crab (Right)

Rusty Revelations: The Beauty of Blue Crab Molting

Whew that was a lot.. Now back to those "rusty" crabs. You have probably seen a crab that looked kind of dirty, or brown underneath. This is not a bad thing folks! A crab that looks like this is more likely to be closer to it's next molting cycle, and therefore makes it more likely to be a heavier crab. When you see a crab with a "white belly" at it's brightest, typically this crab is just 4 days removed from their old shell or post molt. While "rusty" crabs are typically 30-50 days post molt. You will likely see more of these "rusty" crabs in the Fall where blue crabs are at their absolute heaviest.

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Male (Left), Female (Right)

Female Vs Male Blue Crabs

While there are certainly many differences between male blue crabs, we would be remiss if we did not mention the unique differences that exist between them and their female counterpart!

The female blue crab has several visual shell differences including shape, size, and coloring. While the male blue crab, when steamed, is usually a bright reddish orange color, the female blue crab is a dull orange

when steamed. The females also have darker legs and a more rounded body.

Male (Left), Female (Right)

Believe it or not, female blue crabs have what some refer to as "painted nails!" This refers to their claws having bright orange coloring on both sides, while the male blue crab has a light orange coloring on a small part of each claw.

Some more differences include the reproductive organs that are visible on the underside of the crab. Female blue crabs have an apron that can be described as looking similar to the Capitol building, whereas the male blue crab has an apron that looks similar to the Washington Monument.

Who knew there were so many differences?!

Regardless of these differences, what you can expect from your blue crab purchases from CrabPlace.com is the absolute best of the best. At CrabPlace, we take great pride in ensuring each and every crab is hand-graded, packed, and shipped with the care that comes with providing the very best customer service in the industry.

To check out the industries best blue crabs, click the link below!

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