Arthropods are a huge group of animals that includes insects, spiders, crabs, and many other creatures with jointed legs and hard outer shells. The word “arthropod” means “jointed foot” in Greek, which perfectly describes these animals.


Arthropods have been around for over 500 million years, long before the dinosaurs appeared. They are the most diverse group of animals on Earth, making up about 80% of all known animal species. Arthropods come in all shapes and sizes, from tiny mites to giant crabs.

All arthropods share some common features. They have segmented bodies, jointed legs, and a hard external skeleton called an exoskeleton. This exoskeleton protects the animal but also means it has to molt (shed its old skin) to grow bigger.


Think of a butterfly. It has a body divided into segments (head, thorax, and abdomen), six jointed legs, and a hard outer covering. These features make it a perfect example of an arthropod!

Fun Fact

Did you know that some arthropods lived alongside dinosaurs? Insects like ancient ants and beetles scurried around the feet of giant dinosaurs. Some of these prehistoric bugs got trapped in tree sap that hardened into amber, preserving them for millions of years!

People Also Ask

  • What are the main groups of arthropods?
  • How do arthropods grow if they have a hard exoskeleton?
  • Were there any giant arthropods in the past?

What are the main groups of arthropods? The main groups of arthropods are insects (like bees and butterflies), arachnids (like spiders and scorpions), crustaceans (like crabs and shrimp), and myriapods (like centipedes and millipedes). Each group has its own unique features, but they all share the basic arthropod body plan.

How do arthropods grow if they have a hard exoskeleton? Arthropods grow through a process called molting. When an arthropod needs to get bigger, it forms a new, larger exoskeleton under its old one. Then it splits open the old exoskeleton and crawls out. The new exoskeleton is soft at first, allowing the arthropod to expand before it hardens.

Were there any giant arthropods in the past? Yes! In the past, some arthropods grew to enormous sizes. For example, about 300 million years ago, there was a sea scorpion called Jaekelopterus that could grow up to 8 feet (2.5 meters) long. On land, there was a giant millipede called Arthropleura that could reach lengths of 8.5 feet (2.6 meters)!