Do Insects Have Blood? How Their Circulatory System Works
From ants and bees to flies, grasshoppers, dragonflies, ladybugs, and butterflies, Germany alone is home to over 33,000 different insect species, according to the Federal Environment Ministry. Unlike spiders, which are not insects, they have only six legs and a body divided into a head, thorax, and abdomen. These creatures come in a wide variety of sizes, colours, and shapes, and can sometimes be difficult to tell apart.
How Do Insects Circulate Life-Sustaining Fluids?
While insects share some similarities with humans – possessing organs like a heart, brain, eyes, and a respiratory system – they differ significantly in their circulatory systems. Insects are invertebrates, meaning they lack an internal skeleton. Instead, their skeleton lies on the outside, known as an exoskeleton, protected by a thin chitin layer. This unique external structure influences how their circulatory system functions.
According to the German Nature Conservation Union (NABU), insects do not have a closed circulatory system like humans. Instead of blood flowing through veins and arteries, insect blood flows through the body cavities, surrounding the organs. The Federal Agency for Nature Conservation (BfN) notes that insect blood is typically not red, but rather colorless, yellow, or green.
Insect Blood: Why Isn’t It Red?
Human blood is red due to erythrocytes, also known as “red blood cells,” which contain hemoglobin, an iron-containing protein molecule that transports oxygen from the heart to all body cells. The German Red Cross (DRK) explains that when iron reacts with oxygen—similar to how iron rusts—it turns red. The red color of human blood is due to its iron content.
Most insect species, according to the science magazine Spectrum of Science, do not have red blood because they don’t rely on hemoglobin to transport oxygen. They possess a highly branched tracheal system that supplies almost every cell in their body with oxygen. These insects have a colorless fluid, also called hemolymph, that circulates freely within their bodies.
However, there is an exception: the larva of the midge (Chironomus) does have red blood, as noted by Spectrum of Science. This is because they live in oxygen-poor waters and require molecules to transport oxygen. Their blood contains hemoglobin, just like vertebrates, but the red pigment isn’t bound in erythrocytes; it floats freely in the hemolymph.
Interestingly, if copper instead of iron is used for oxygen transport in the blood, as in squid, snails, or some crabs, the blood is blue. The DRK explains this is because copper turns greenish-blue when it reacts with oxygen.
Frequently Asked Questions
Do insects have a heart?
Insects do have a heart, but it functions differently than a human heart.
What is hemolymph?
Hemolymph is the fluid that circulates in the body of insects, serving a similar purpose to blood in vertebrates. It is often colorless, yellow, or green.
Why is insect blood usually not red?
Most insects do not need hemoglobin to transport oxygen, relying instead on a tracheal system. Their blood lacks the iron that gives human blood its red color.
Considering the diverse and often surprising biological mechanisms within the insect world, what further discoveries might reveal about these vital creatures and their role in our ecosystems?