Re: What color is a butterfly's blood?

Dear Clifford,

Butterflies, and all other insects, have blood that is colorless. They do not use their blood to transport respiratory gases (oxygen and carbon dioxide) through their bodies, so the blood does not contain any respiratory pigments. This is different from our blood, which contains the red pigment hemoglobin. In fact, insects' blood is different from the other major group of arthropods, the crustaceans, too. Crustaceans have a bluish pigment called hemocyanin in their blood, which gives the blood a faint blue tinge.< BR>

So if insects don't use their blood to transport gases, what do they use it for? An insect's circulatory system is used to transport nutrients throughout the body. However, instead of relying on the inefficiency of an open circulatory system (characteristic of all arthropods) to bring oxygen to tissues that are working hard while the animal is flying, butterflies and other insects have evolved a nifty system of tracheal tubules that serve to bring oxygen directly to all the tissues of the body. The tracheal tubules open to the outside through tiny holes, or spiracles, and branch into smaller and smaller tubes until just about every cell is reached. Gas exchange occurs directly between the cells and the tubules, which in reality are pockets of the outside environment that are brought into the animal's body. Pretty neat, huh?

Tracheal tubules, as cool as they are, only work because insects are very small animals. For animals that are much larger, and as active as insects, tracheal tubules wouldn't be able to bring enough oxygen to the tissues to keep the animal alive. That's why larger animals use a circulatory system, powered by a pumping heart, to transport respiratory gases through the body. Tracheal tubules are found only in insects and in some of the terrestrial chelicerates (spiders, scorpions, mites, and their kin).

Click here for some more material on insect anatomy. It doesn't have a diagram of the tracheal tubule system, but you can see where the spiracles are located on the grasshopper's body.

The answer to your question was easy, but I couldn't resist giving you some additional information about insect anatomy and physiology. I hope you don't mind!

Thanks for the question!

Allison J. Gong
Mad Scientist