Do Insects Bleed?

When we think about different living beings as they experience injury, we often think about bleeding as well. But are insects capable of bleeding too?

Insects do bleed. Much like human blood, the blood of insects is capable of clotting in order to heal wounds. Insect blood is referred to as hemolymph, a liquid that fills the inside of the insect and provides necessary nutrients.

The remainder of this article will explain a number of topics relevant to insects as far as how they deal with injury in terms of blood and bleeding.

What Are the Main Characteristics of Insect Blood?

First off, it is important to note that while the process of bleeding in insects is similar to that of humans in some ways, insects’ blood is not called blood. Scientifically speaking, insect blood is referred to as hemolymph. 

Due to the absence of oxygen-rich red blood cells, hemolymph is typically green or yellow. This liquidy substance fills up the entirety of the insects’ abdomen. Hormones and vital nutrients can be found floating around in this substance.

How Does Insect Blood Compare to Human Blood?

The blood of insects varies drastically from that of human blood. Insect blood lacks the bright red color that characterizes human blood as such. Our blood is bright red because it is full of hemoglobin. Hemoglobin aids in carrying oxygen throughout the human body and serves as a binder between oxygen molecules. 

Insects have a highly complex system of tubes that are used to transport oxygen throughout their bodies. Oxygen is able to enter the insects’ bodies through small holes called spiracles. Their blood, rather than carrying oxygen, carries a number of essential nutrients throughout the body. 

When they are injured, the insect will bleed. Just like humans, clotting is used to fill the wounded area with blood in order to rapidly repair the surface. For insects, clotting is only effective in healing minor injuries such as scrapes.

How Does Hemolymph Work?

Hemolymph is the same clear, yellow, or green fluid that can be seen escaping the body of an insect that has recently been stepped on. This is how an insect “bleeds.”Hemolymph is the technical term for the “blood” that fills the abdomen of each insect’s body. 

Rather than remaining trapped within veins and arteries, hemolymph flows freely throughout the entire body cavity of an insect. Similar to the way that humans require a constant supply of food, water, oxygen, and blood, insects require a constant supply of hemolymph.

Insects are supplied the following items via hemolymph:

  • Salts
  • Nutrients
  • Hormones
  • Metabolic Wastes

Why Is Hemolymph Crucial to the Survival of Insects?

Hemolymph is the leading factor contributing to the insect’s body holding its shape. In the section above, elements that are crucial to an insect’s survival were listed. Thus the necessity of hemolymph flowing throughout the body cavity.

Sufficient oxygen supply, in combination with appropriate blood flow, provides one extremely important ability to the insect: mobility. Mobility is absolutely crucial to any insects’ survival. In the event that an insect would need to throw itself toward its prey or flee from a predator, it would be executed seamlessly, as long as the hemolymph is constantly flowing through the body, delivering a number of essential nutrients.

Additionally, insects possess this necessity that the circulatory system is constantly being cycled through. The immune system that exists within the insect can be simplified almost completely down to hemolymph. Hemolymph, among many other functions, aids in protection from harmful parasites and bacteria. 

Molting, laying eggs, hatching eggs, and reproduction would not be able to occur without the presence of hemolymph in the body cavity. All of these processes are essential to the survival of the insect.

Regular circulation of blood, oxygen, and other nutrients is absolutely crucial to the survival of countless species of insects around the world. Within insects, hemolymph is regularly flowing freely throughout the entire body cavity in order to ensure that processes like reproduction, molting, and motion can take place.

The Insect Circulatory System

Unlike humans and other animals, insects possess a circulatory system that lacks arteries and veins. The circulatory system of insects is completely free-flowing. For arthropods, the family that most insects belong to, this characteristic is highly common. The insects’ body cavity is filled almost entirely with fluids such as the plentiful hemolymph.  

Along the inside of the body cavity of any insect lies a crucial vessel or organ. Hemolymph is regularly pumped and distributed throughout the body cavity thanks to this important organ. It can be found toward the insects’ lower abdomen.

Much like humans and many other vertebrates, all insects do, in fact, have a heart. For insects, the heart acts as a vital organ. Located at the middle region of the body cavity, the heart is responsible for initiating the circulatory processes. More specifically, the heart is located inside the dorsal vessel. Additionally, the entrance and exit of hemolymph are regulated by small holes in each insect’s heart. 

Hemolymph is then pumped to the top of the cranial region of the insect from the abdominal region. Hemolymph immediately begins its journey toward the body cavity prior to reaching the head.

The idea that contact must be made between hemolymph and all vital organs is the leading reason that this substance must be pumping through the insect’s body at all times. These organs and tissue must remain healthy and nutrient-rich in order to supply the insect with the necessary levels of blood and oxygen. 

Extremely thin layers of both membrane and muscle are capable of acting as partitions between the main body regions. Those regions are commonly referred to as the three blood sinuses. The blood sinuses work in unison to promote the contractions of the insects’ heart. Additionally, the blood sinuses keep the heart from contracting at an irregular rate. 

An insect’s environment is crucial because changes in both the climate and temperature of the outside world are other factors that may change the rate of contractions within the insect’s heart.

What Is the Function of an Insect’s Heart?

Unlike the human heart, the insect heart is located toward the back of their bodies rather than the front. Where the human heart is used to pump blood, the dorsal vessel performs the same function in insects.

The dorsal vessel consists of an aorta (located in the thorax) and a heart (located in the abdominal region). In the event that pathogens invade the insects’ body, reaching the hemocoel, hemolymph is immediately dispersed to all affected parts of the body. 

Muscle contractions create hydrostatic pressure, which helps to circulate hemolymph. It is essential that the hemolymph travels freely from the head to the thorax.

The wall of each insect’s heart possesses many perforations. These perforations are known as Ostia. Ostia serves as a passageway for hemolymph. This allows hemolymph to enter from the hemocoel.

insect anatomy diagram
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Conclusion

Insects can bleed. While there are some similarities between how humans and insects bleed, there are several differences. 

Scientifically speaking, insect blood is commonly referred to as hemolymph. Hemolymph can be directly compared to traditional blood that is present in many other organisms. The primary purpose of hemolymph is to transport vital nutrients and hormones throughout the insect’s body. 

Insects’ blood lacks the oxygen-rich red blood cells that fill the human circulatory system. This is because insects already take in oxygen through spiracles. Insect blood, still, is capable of clotting in order to repair minor injuries. 

Sources

UCSB: UCSB Science Line

Science Advances: The immune and circulatory systems are functionally integrated across insect evolution