The first two or three pairs of legs are longer than the others and are generally extended out from the sides of the body, much like a crab's claws. Some crab spiders, like fiddler crabs, can move forward, backward, or sideways. They resemble other free-living spiders such as jumping spiders and wolf spiders in this regard. However, unlike those spiders which rely on their acute senses to detect prey (jumping spiders and wolf spiders), crab spiders use vision alone for hunting. They scan their environment with their front-facing eyes, looking for movement or light signals that might indicate a potential meal.
Crab spiders cannot jump as such, but they do have special structures on their backs which enable them to glide between branches or across leaves. These structures look like little hooks which fit into notches on their abdomen. When the spider wants to climb down a tree it winds its long silk fiber around one of these hooks, then lets go. The force of gravity pulls the hook straight down, allowing the spider to slide down its web to the ground or another tree.
It is estimated that there are about 7,500 species of crab spiders worldwide. They can be found everywhere from extreme cold climates to the tropics. Although they may look tiny, many species can grow to be more than an inch long.
Crab spiders are known for being aggressive predators of other insects. They will attack other spiders, worms, and small insects. However, they usually don't eat crabs themselves.
Crabs move quicker and more easily when walking sideways because their legs are rigid and jointed. When walking sideways, one leg never moves into the path of the other. As a result, a crab is less likely to trip over its own foot. That's vital when you're juggling four sets of walking legs and a set of claws!
The photo at the top of the page shows a blue crabs approach to a meal. You can see that it is walking sideways, with both claws raised high above the ground. This gives it balance as it scurries across the sand toward its dinner.
It's not just crabs that walk sideways. Most insects do too. They use their six legs equally divided between their two sides to walk smoothly.
In fact, most animals that have two legs like humans walk on their left side because this is the side where the muscles are located. If you were to watch someone walking, they would use their left leg first and then their right leg.
People sometimes talk about walking "like a human", but they mean that you should copy what humans do instead of animals. Walking like a human is not correct - animals don't walk like humans do!
Walking like an animal is fine though. Animals do it very well so it must be easy to do.
You should walk like an animal if this makes you feel better about yourself!
Crabs have 10 jointed limbs, including two big claws for food capture known as chelipeds and eight walking legs utilized for sideways locomotion. The rest of the body is protected by an elliptical carapace. Crabs have two stalked eyes and sensory antennae. They breathe through a pneumatic system composed of air-filled cavities called coxae.
The word "crab" comes from the French word crabes, which means "joints." The term applies to any arthropod with ten legs bearing cheliform (claws) digits; some taxonomists include the horseshoe crab, which has nine legs. However, only the crayfish, lobster, and shrimp possess true joints: bones with articulations that permit free movement between different parts of the limb or body.
In general, the legs of crabs are similar to those of insects in structure but are much shorter. The chelipeds or claw limbs are used for capturing prey and fighting off predators while the other limbs are used for walking. Male crabs have small chelipeds that they use for grasping females during mating. The female then carries the male until they find a place to lay their eggs.
Young crabs can be distinguished from adults by looking at their carapaces. An adult crab's carapace will be red or brownish in color, while that of a young crab will be white or yellowish.
Crabs are crustaceans that have ten legs. On the ends of the front pair of legs are grasping claws or pincers. These are used in defense and for capturing prey.
Claws vs Pincers: Claws are more specialized than pincers. With claws, the end of the leg moves back toward the body to create a claw. With pincers, the whole foot turns inward to create a pincer. However, both types of limbs can be modified into weapons such as knives or hooks.
Crabs use their claws and pincers to capture food. They also use them to defend themselves from predators. Crabs lose their claws after each molt as they grow new ones. This happens when the old claw or pincer falls off and the new one doesn't come out yet. The crab only loses its last claw or pincer; it keeps all its others.
People sometimes call crabs "herbivores" because they don't eat meat. But actually, crabs are carnivorous animals that just happen to eat plants at first. Their digestive systems are designed for eating other organisms so they must consume meat to maintain these organs. Crab shells contain calcium carbonate which is used to build bones and teeth among other things.