Crabs are among the most intriguing and diverse creatures on planet Earth. As members of the crustacean family, they have captured human fascination through their unique biology and behaviors.
They inhabit various environments across the world, from the deepest ocean trenches to our very own dinner plates.
This article delves deep into the fascinating world of crabs, offering a glimpse into the peculiarities that set these creatures apart. Let’s embark on a discovery journey with these twelve captivating facts about crabs.
Facts About Crabs
Fact #1: There Are Over 6,800 Species of Crabs Across the World
The enormous biodiversity of crabs is mesmerizing, with over 6,800 known species that inhabit all the world’s oceans, freshwater, and land areas. This diversity is reflected in their vast range of sizes, colors, and shapes, each adapted to its own specific environment.
Crabs are known to evolve rapidly to fill ecological niches. Hence, scientists often discover new species, adding to the already extensive list.
Fact #2: Crabs Can Live Both In Water and On Land
Some species of crabs such as fiddler crabs and land hermit crabs have adapted to live on land. These terrestrial crabs still require some level of moisture to survive and usually make regular trips back to the water to keep their gills wet.
They have developed various adaptations, including the ability to store water in certain parts of their bodies and to breathe air.
Fact #3: Crabs Communicate Through Sound and Movement
Crabs have a unique way of communicating that includes making sounds by drumming or clapping their claws, as well as performing visual movements or dances.
These behaviors can serve for attracting mates, deterring predators, or establishing territorial dominance.
Certain species are known to perform highly intricate and ritualistic displays when it comes to mating season.
Fact #4: Crabs Have Blue Blood Due to Copper-Based Hemocyanin
Unlike humans who have iron-based hemoglobin turning their blood red, crabs have hemocyanin which contains copper, turning their blood blue.
Hemocyanin is more efficient than hemoglobin at transporting oxygen in low-temperature and low-oxygen environments, such as the ocean depths where many crabs live.
This blue blood has practical uses in biotechnology and pharmaceuticals, particularly in the detection of bacterial endotoxins.
Fact #5: The Largest Crab in the World Can Span Up to 12 Feet
The Japanese spider crab is the largest known crab species, with a leg span reaching up to 12 feet from claw to claw. This mammoth sea creature can weigh up to 42 pounds and has been known to live for up to 100 years.
Their impressive size serves as a deterrent to predators while also enabling them to hunt a wide range of prey.
Fact #6: Crabs Have Complex Mating Rituals and Care for Their Young
Crab mating rituals are complex and can involve extended periods of dance, combat, and sometimes cooperation. Female crabs typically carry and nurture their eggs in a brood pouch until they hatch into larvae.
They may release their eggs into the water or onto land, depending on their species. After hatching, crab larvae often go through several planktonic (free-swimming) stages before settling down and growing into adult form.
Fact #7: Crabs Can Autotomize Their Limbs to Escape Danger
Autotomy, or the ability to shed a limb or other body part, is a survival tactic used by crabs to escape predators or to free themselves from tight spots. If caught by a claw, for example, a crab can cast off the appendage and later regrow it, a process known as regeneration.
This self-amputation doesn’t greatly harm the crab, as their limbs have predetermined breaking points designed for such emergency escapes.
Fact #8: Some Crabs Are Named After Their Unique Physical Traits
The fiddler crab is named for the males’ distinctive large claw resembling a fiddle. Likewise, the horseshoe crab, though technically not a true crab, earns its name from its horseshoe-shaped carapace.
Descriptive names provide quick insights into a species’ defining characteristics, making them easier to remember and identify.
Fact #9: Crabs Have Been on Earth for a Very Long Time
Fossil records show that crabs have been roaming the earth for at least 200 million years, surviving through ages and even outlasting dinosaurs. This lengthy period has allowed them to evolve and adapt to several earth-changing events and probably contribute to their vast diversity.
Studying crab fossils can provide valuable clues about prehistoric marine environments.
Fact #10: Crabs Play a Vital Role in Their Ecosystems
As both predators and prey, crabs significantly influence the food web in their respective habitats.
They contribute to the health of their environments by scavenging dead organisms and aerating the soil during burrowing.
In coastal ecosystems, their feeding habits can affect the composition of seagrass beds and coral reefs, influencing the biodiversity of these areas.
Fact #11: Crabs Have a Unique Way of Eating
Most crabs have a set of pincers which they use to catch, crush, and tear apart their food before consuming it. Inside their tiny mouths, crabs have structures known as maxillipeds that help them taste and manipulate their food.
They are not picky eaters and have a varied diet that includes algae, bacteria, detritus, worms, and small fish.
Fact #12: Crabs Must Molt to Grow
Crabs have a hard exoskeleton that does not grow, so in order to get bigger, they must undergo a process called molting. During molting, a crab shed its old exoskeleton and grows a new, larger one.
This is a vulnerable time for crabs because they are soft and defenseless until their new shell hardens. Growth can be rapid after molting, thanks to the soft new shell allowing for expansion.
FAQs about Crabs
What is the average lifespan of a crab?
Crabs generally live between 3 to 4 years, but this varies widely among species. Some, like the Japanese spider crab, can live for up to a century under ideal conditions.
Can crabs feel pain?
Recent studies suggest that crabs can indeed feel pain. When crabs snatch their claws away from harm or make efforts to avoid repeat offensive stimuli, it indicates a level of pain perception and learning.
How can you tell the age of a crab?
Determining the exact age of crabs can be challenging because they do not have growth rings like trees. However, size and development stage can offer an approximate indication of age, especially for species with known growth rates.
Why do crabs walk sideways?
Crabs walk sideways because the structure of their legs makes it more efficient. The sideways movement is more graceful for crabs due to the positioning of their legs and joints which are arranged in a way that favors lateral movement.
Are all crabs edible?
Not all crabs are edible—some may be too small to provide enough meat, while others could be poisonous. It’s important to know which species are safe and legal to harvest and consume.
How do crabs breathe?
Most crabs breathe through gills which allow them to extract oxygen from water, but some terrestrial crabs also have modified gills or cavities that act like lungs, enabling them to breathe air.
Regardless of their breathing mechanism, a damp environment is crucial for the gas exchange process.