The color of bug blood

Dear MA.: Out on the highway (I'm on vacation), a question stared me in the face. I've become well acquainted with bug splatters over the last week. Some are yellow, some are red, some are clear. But why? What color blood do bugs have? (Do bugs even have blood?) I'm sending this on a postcard (aren't those bison cute?) so you’ll have an answer waiting for me when I get back. — Humphrey Wuff, On the Road

Sounds like some wonderful vacation, Humphrey. Most people kick back and enjoy the scenery, and here you are fretting about bug blood. Yes, bugs have blood — actually it’s a fluid called hemolymph. It circulates in an open (tracheal) system through the little creatures, not in the bug equivalent of veins and arteries. Bug blood varies in color from species to species. Most often it’s colorless or is a pale green shade. But it can also carry a cheerful yellow, red, or amber pigment. Since bug blood makes up only about five percent of most insects’ body weight, a lot of that colorful stew on your windshield probably comes from the stomach contents of whatever critters have met their fate on your car — various nectars, pollen, other bugs, animal blood. All I can say is, welcome back to San Diego, and aren’t you glad those bison can’t fly?