Jacqueline DuBay, age 8, of St. Paul, Minnesota, for her question:

Do spiders have bones?

An ordinary spider is an itty bitty creature. Imagine how tiny her bones would be    if she had any bones. Actually, there are no bones at all inside her small body. This is not unusual. Thousands of other spider sized animals do not have any bones either. Our big bodies need an inside framework of bones and we need bones with joints to move arms, legs and other parts. But the busy little spider does not need them. She has other ways to hold her body in shape and move about.

It may seem strange to us, but most of nature's animals have no bones inside their bodies. The long list of boneless ones includes hundreds of different spiders and more than half a million different insects. Lots of larger creatures, such as shrimps and crabs and lobsters, have no bones in their bodies either. The experts tell us that spiders are not insects, and this is true. But they are distant cousins of the insects and so are all the other animals on this list. However, they are not related to the worms, snails and many other boneless creatures.

The spiders and insects, the crabs and lobsters are related because of what they have instead of bones. Your bony skeleton, remember, forms a framework inside your body. All these little boneless cousins have an outside framework instead. It is called an exoskeleton. Part of it is make of crisp crusty material. The rest is made of tough, leathery material. The spider's exoskeleton covers her head and chest sections with a crusty shield. Her round tummy is held securely inside a tough leathery bag. This covering works because her body is so small. But if spiders and insects were human size, their bodies would need inside skeletons to support them.

An exoskeleton tends to be rather stiff and the busy spider must be able to move around. Our bones are stiff too, and we move them only at the joints. The spider has joints also, special bendable joints in her exoskeleton. Her eight legs have stiff stockings with round garters of bendable material at the joints. Like us, she has muscles inside her body to make her joints move. Each muscle has two ends, one fixed on each side of a joint. As she scuttles around, dozens of muscles stretch and squeeze to bend the many joints in her skinny legs.

Many insects are covered all over with stiff exoskeletons. But this stiff material has bands of bendable material around the joints. Like the spiders, they have muscles inside to make the joints move. Shrimps have the same sort of jointed exoskeletons. Crabs and lobsters need sturdier framework for their larger bodies. So their crusty exoskeletons are thicker and stronger. But they too have the same bendable joints.

Experts have a fancy name for all the creatures that have joints of this kind. They call them arthropods, which means animals with jointed feed.