Ask Dr. Universe: When it comes to blood, humans and insects have stuff in common

Washington State University

Dear Dr. Universe,

Do insects have blood in their bodies? – Raman, 7, Washington

Dear Raman,

You probably don’t look like an insect. You don’t have feelers or wings. You keep your skeleton inside your body instead of on the outside. But what about blood? Do insects have blood like yours?

I talked about this with my friend Richard Zack. He’s an entomologist at Washington State University.

“Insects have hemolymph,” he said. “It’s very similar to blood.”

Zack told me hemolymph moves differently through the body, and it doesn’t do everything blood does.

Humans and other mammals have closed circulatory systems. That means their blood travels in blood vessels. A heart pumps the blood all over the body, and it moves through a network of blood vessels to get there.

As it moves through the body, blood carries things with it. It carries chemical messages called hormones. It carries nutrients. If you get hurt, it carries cells that repair wounds. If germs get into your body, immune cells travel in the blood to fight the germs, so you don’t get sick.

Insects have open circulatory systems. They don’t have any blood vessels. Their hemolymph just sloshes around in their bodies. They have a heart, but it’s not like yours. It’s one long tube along the insect’s back. This tube pulls in some of the hemolymph as it sloshes around and pushes it to the front of the insect.

There, the hemolymph can pick up hormones and other stuff from the insect’s brain. It carries those things with it as it flows freely back through the insect’s body. Hemolymph carries hormones, nutrients, and cells for wound repair and germ-fighting – just like human blood does.

But human blood does one more thing. Blood contains a protein called hemoglobin. That protein grabs on to oxygen from the lungs. It carries the oxygen through the network of blood vessels and delivers it to your cells. Hemoglobin contains iron. It’s red – and that’s why human blood is red.

Hemolymph doesn’t contain hemoglobin. It doesn’t carry oxygen at all.

Instead, insects send oxygen to their cells through tiny air tubes. Insects have openings on each side of their bodies – called spiracles. They open these spiracles to let in air. Each spiracle is linked to a network of air tubes. Oxygen moves through these tubes to get to each cell in the insect’s body.

Since they don’t have iron-rich hemoglobin, hemolymph isn’t red like human blood. Hemolymph contains lots of copper. So, hemolymph is blue green. But that color can change depending on what the insect eats.

“The functions of hemolymph and blood are almost exactly the same,” Zack said. “Except for this one biggie: Insect blood doesn’t move oxygen. That’s a whole different system in insects. But when you think of all the other things that blood does – moves messages through the body, moves nutrients, heals wounds – hemolymph does the same things.”

It turns out you have a lot in common with insects after all.

Sincerely,

Dr. Universe

P.S.: Did you know goldfish can have surgery? Check out the latest episode of the Ask Dr. Universe podcast to meet a fish veterinarian and learn all about fish medicine.

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