Dear Landon,

I love taking selfies with my insect friends. They’re so tiny and look so different from a big cat like me.

But my friend Rich Zack told me that insects and humans have lots in common. He’s an insect scientist at Washington State University.

“There are body systems that every animal needs,” Zack said. “Insects are relatively advanced animals, so they do a lot of things like humans do.”

That means many of an insect’s body systems are like yours. But there are three body systems that are super different for insects. Those are the skeletal, circulatory and respiratory systems.

Let’s start with your skeleton. The bones inside your body give your body structure. Without them, you’d be kind of floppy. Since your bones are on the inside, you have what’s called an endoskeleton.

But an insect has zero bones. It has a tough covering on the outside of its body called an exoskeleton. The hard outside of a beetle is an exoskeleton. The leathery outside of a grasshopper is an exoskeleton. The delicate outside of a caterpillar is an exoskeleton.

All those exoskeletons do some of the jobs your skin does. They keep the stuff inside an insect from falling out. They keep outside germs from getting inside the insect’s body.

The second big difference has to do with blood. Your heart pumps blood through a network of blood vessels. It’s a closed circulatory system. That means the blood stays inside the vessels as it moves oxygen and other important things to all the cells in your body.

An insect has an open circulatory system. Its blood—called hemolymph—just sloshes around inside its body.

The part of your blood that carries oxygen is red, so your blood is red. But the color of an insect’s blood comes from whatever it eats. It’s usually white or greenish. This bee’s blood is almost clear. ©2017 Borsuk et al./used under CC by 4.0/cropped from original

Remember how an insect doesn’t have bones to give its body structure? Its blood does that job. It’s like when you fill up a water balloon. The water inside pushes against the balloon and gives it shape.

Like your blood, insect blood moves around important stuff like nutrients and chemical messages. That’s why an insect has one blood vessel that runs along its back inside its body. That vessel is called the insect’s heart, but it’s much simpler than your heart.

The insect heart pushes the blood from the insect’s tail end up to its head. That sends all those nutrients and messages to the insect’s brain. Then, the blood flows back through the insect’s body cavity.

But insect blood doesn’t do the biggest job your blood does. Insect blood does not carry oxygen.

That brings us to the third big difference. You take in air with your lungs. Then your blood carries the oxygen all over your body.

Insects don’t have lungs. They take in air through a row of tiny holes along their sides—called spiracles. When the holes open, air enters a network of tubes. The tubes get smaller and smaller and smaller. They pipe oxygen to every cell in the insect’s body.

“That’s one of the reasons insects can’t get very large,” Zack said. “That tube system only works for a certain size range.”

That explains why my insect friends are so tiny—but we still feel like we have so much in common. Our amazing differences don’t bug us at all.


Dr. Universe