An exoskeleton is a hard outer covering that protects and supports an animal's body from the outside, like a suit of armor. Instead of having bones inside their bodies like we do, insects, spiders, crabs, and lobsters wear their skeletons on the outside. A beetle's shiny shell, a crab's tough outer covering, and the crusty segments on a grasshopper are all exoskeletons.

Think of it like the difference between your body and a knight's armor. Your skeleton is hidden inside, holding you up from within. An exoskeleton does a similar job, but it surrounds much of the animal, protecting soft tissues inside while giving muscles something to attach to.

Exoskeletons work brilliantly for small creatures, but they have limitations. As an animal grows, it must molt, shedding its old exoskeleton and growing a new, larger one underneath. During this vulnerable time, the animal is soft and defenseless until the new exoskeleton hardens. This is also one reason insects and other animals with exoskeletons don't grow as large as elephants or whales: an exoskeleton big enough to support that much weight would be extremely heavy.

Engineers have borrowed this idea to create mechanical exoskeletons that people can wear to lift heavy objects or help people with injuries walk again.