Frequently Asked Questions

Q: How do crabs breathe? How long can they stay out of water?

A: Crabs use their gills to extract oxygen from the water, much like a fish. However, crabs can survive for long periods out of water, and some live almost exclusively on land. As long as a crab can keep its gills moist, oxygen from the air will diffuse into the moisture, and then into the gills. One way to keep their gills from drying out is to seek out cool, dark and moist hiding places when on land. This way they can keep breathing and stay hidden from predators. Also, they have articulating plates around their gills that help seal them in and prevent drying out. Land crabs have even more adaptations to prevent drying out. They drink water from dew and the ground, they get it from food, and even from water vapor. They also store water in their bladder, blood, and specialized pockets throughout their bodies.

This information obtained from OceanLink Answers to Anthropoda Questions

Q: How do crabs find food in the dark?

A: Crabs do not rely on vision like you and I do, when looking for food. Crabs cannot see very well and usually only use their vision when their prey is very close. Crabs find their food in the dark (or in the light) by something called "chemoreception". This is kind of like our sense of smell. They have very sensitive chemoreceptors (or smell organs) on their antennae and in their mouthparts and distributed throughout their body. So, crabs can "smell" the chemicals that their prey put out in the water and follow these "smells" to find food.

This information obtained from OceanLink Answers to Anthropoda Questions

Q: Do more crabs molt during a full moon?

A: Some say yes and some say no. Click here for more information.

Q: Where do crabs go in the winter?

A: When the water temperature starts to fall and the days start getting shorter, the blue crab retreats to deep water and burrows into the muddy or sandy bottom to spend the winter. A crab buries itself by forcing its abdomen backwards into the bottom with quick snapping motions. While doing this, the crab will also pick and claw at the bottom with its hind walking legs and flip it away with the paddles of its swimming legs. Within a few minutes the crab is resting at a 45° angle in the bottom, with only antennae, the tips of its eye stalks, and small breathing channels visible in the mud. Crabs do not hibernate, rather they lie dormant for the long winter (usually  from November through May.)

Q: I've heard that a mouth bite from the blue crab can cause death, is there any truth to this?

A: The blue crab doesn't have a mouth (or teeth) in which to bite, however people have been known to get blood poisoning from a claw pinch if the the skin is broken (always wear gloves!) As for a crab's mouth, located in the anterior portion of the cephalothorax of the crab are its mouth parts, grouped around the opening of the esophagus. These mouth parts are generally similar to those of shrimps and lobsters. The outermost pair is the third maxillipeds, used for holding food. Under and in front of these are two more pairs of maxillipeds and two pairs of maxillae, also used for holding food, and a pair of mandibles, or jaws, which push the food into the esophagus.