英语听力文摘 English Digest 682 昆虫血为何是绿色或黄色

（单词翻译）

Why Is Insect Blood Green Or Yellow?

You’ve probably heard someone use the phrase “blood red,” but have you ever wondered if all blood really is red? For example, think about the bugs² you’ve seen splatter against your car’s windshield, leaving behind a clear, yellowish, or greenish liquid. That liquid, is hemolymph, or insect blood.

Insect Blood

The blood of an insect functions differently than the blood of a human. In humans, blood gets its red color from hemoglobin, which travels through blood vessels³ carrying oxygen from the lungs to the rest of the body. Insect blood, however, does not carry gasses and has no hemoglobin. Instead, bugs have a system of tubes that transport gasses directly between their cells and the outside air.

In fact, insects don’t even have blood vessels. Instead there is a hollow space inside their external skeleton in which their blood oozes⁴ around. This cavity extends to the antennas⁵, legs, and wing veins⁶. The bug¹’s heart, a long tube that stretches the length of its body, pushes the blood from the rear end of the insect on forward. The bug may also have little hearts at the ends of its extremities⁷ to help move the blood along.

Pigment⁸

Pumping blood is a slow process: it takes about eight minutes for an insect’s blood to circulate completely. Like human blood, bug blood carries nutrients⁹ and hormones¹⁰ to the insect’s cells. The greenish or yellowish color of insect blood comes from the pigments¹¹ of the plants the bug eats.