An earthworm is a terrestrial invertebrate that belongs to the order Opisthopora of class Oligochaeta of invertebrates. Their body is tube-like, with simple organ systems, and segmented with metameres.
Well, if you have been thinking that earthworms have a nose like us to breathe and take in and out the air, then you are absolutely wrong.
Their breathing system is really very simple but well to do for their body type.
You’ll find that their external body skin is always moist due to the presence of slimy mucus. Well, this is a huge advantage in their breathing and respiration systems.
Let’s learn all about the respiration system in earthworm in detail. So, let’s get started!
Respiration in Earthworms: How do they actually breathe?
Respiration in earthworm is really very simple. It takes place by diffusion of gases through the general body surface of the skin.
Gaseous exchange, that is, the intake of O2 and giving out CO2, takes place between the blood capillaries of the outer epidermis and the surface film of moisture contributed by the secreted mucus, excreted wastes, and coelomic fluid.
Haemoglobin present in the blood helps in the intake of oxygen (O2) in blood and transport it throughout the body tissues.
It also takes the carbon dioxide (CO2) out of the body tissues and expires it through the outer epidermis of the earthworm’s surface.
Mostly the dorsal pores and nephridiopores (the external opening of a nephridium excretory pores) exude a fluid that moistens and protects the worm’s surface, allowing the earthworm to breathe with ease.
They don’t have any type of lungs. They just have 5 simple hearts that pump out blood throughout the body tissues.
Yes, they do have a mouth but, they can’t breathe through their mouth, and certainly can’t breathe through their nose as well.
They can only breathe through their moist skin so it is very necessary that their skin doesn’t dry out or else they will suffocate and die.
The coelomic fluid is another one that is also generally secreted by the earthworms for maintaining moisture to help their physiological activities such as respiration to carry on with ease.
This coelomic fluid consists of a watery matrix, the plasma, and a large number of coelomocytes that also provide oxygen and take out carbon dioxide in and out of the body surface.
How do earthworms breathe underground in the soil?
Earthworms have dramatically evolved to breathe through their moist skin and so it is very necessary that they keep their skin moist and slimy all the time in order to breathe and exchange the gases.
So, due to this particular reason, it will always find a cool and comfortable habitat to keep its skin moist and wet all the time.
That’s why it becomes very much necessary for them to regulate their body temperature so that they always remain moist.
So, you will often find that the earthworm tries to regulate its temperature, and in doing so it either goes underground or outside the soil in the open air.
It would go underground if the temperature outside is too warm, and the earthworm would come outside if the temperature underground is too warm or cold.
So, when it is out of the soil it easily gets oxygen and expires out carbon dioxide very easily in the open air. As fresh air is taken in through the skin, oxygen is drawn into the worm’s circulatory system, and that’s how it breathes.
Oxygen is also present in the deep soil as well. Oxygen availability in soil depends upon the physical characteristics of the soil such as texture, structure, porosity, and water content.
The oxygen that is available in the soil along with nitrogen, carbon dioxide, etc. is very much critical because it allows for the respiration of both plant roots and soil organisms.
And, now if the earthworm is underground deep into the soil it will intake the oxygen gas that is found in the air spaces between soil components through its slimy skin.
Just like in the open air, the oxygen is not in a continuous flow in the soil. In fact, it’s blocked in patches between the soil.
So, in order to properly breathe and intake the oxygen in the soil, they need to move (locomote) from one place to another under the soil.
The way that earthworms gain oxygen is by moving in the soil from one place to another to get the oxygen properly. Every time they move, they get oxygen.
How earthworms breathe when it rains?
Yeah, it’s true that earthworms prefer cool and moist places just like the deep soil, so that, they can breathe easily and keep their skin surface wet. For this reason, worms prefer to live underground.
But, after it rains, the soil surface becomes wet enough and gets much soaked in water to support worm life. That’s the reason why earthworms come out of the soil when it rains.
Earthworms can intake the oxygen in gaseous form from the air pockets in the soil. But, after heavy rainfall, the soil gets filled with dissolved oxygen which makes it really hard for them to better breathe as there is less oxygen touching the worm’s body.
Yes, they can still stay under the soil for a long time if there’s a moderate level of rainfall. But, if there’s heavy rainfall for many continuous days the worms will better opt. to go out to the soil surface for getting a greater concentration of oxygen from the free air.
There’s another theory that says that earthworms come out of the soil to migrate from one place to another only during the rainy season because it’s only that cool-season when they can keep their body moist without drying it up.
This migration theory states that they have a natural adaptation that helps them feel the vibrations caused in the soil that might give them the signal for safe migration. So, feeling those vibrations they come out of the soil during or after rainfall.
That’s the cause why you will often see that after heavy rainfall, mainly during the spring season, numerous earthworms will come out to the soil surface and will lay there until disturbed.
Can earthworms breathe underwater?
Earthworms need oxygen gas just like humans do, so they are happy to stay in moist regions where they can get much oxygen gas easily.
So, drowning might not be a big concern for earthworms, but breathing actually is, as underwater there’s only dissolved oxygen, not much gaseous oxygen.
So, they can’t stay or breathe underwater for a long time or they will die due to suffocation.
But in some cases, it has been seen that they can stay perfectly inside the deep soil at the bottom of the ponds or stagnant water bodies.
It’s because they go very deep inside the soil where they are able to stay for months with a sufficient amount of oxygen gas availability.
But, if you try to keep them locked in a water bottle with its cap open then you will find that the earthworm will come up in the water surface for a while to take the oxygen from the free air.
Or, inside the bottle, you will find that the half part of the earthworm’s body is inside the water and the other half outside water. The earthworm breathes in the open air by keeping half of its body out of the water.
But, if you create a condition where you keep the earthworm inside the water bottle and close its cap tightly then, you’ll surely find that it will die due to suffocation within a day or two or so.
How earthworm’s circulatory system helps them in breathing and respiration?
The circulatory system of the earthworm is also known as the blood vascular system and this is of a closed type consisting of blood vessels and capillaries which pass to all parts of the body and its tissues.
The blood flowing through the circulatory system consists of red hemoglobin pigment that occurs in the plasma at a dissolved state.
It gives the red color to the blood and helps it in the transportation of oxygen throughout the body for respiration purposes.
It is also to be noted that there is no direct contact between the body tissues and blood as the circulatory system is of closed type. So, the exchange of carbon dioxide and oxygen takes place due to diffusion.
Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. Diffusion allows an earthworm to get the oxygen it needs to survive.
The haemoglobin in the blood intakes oxygen from the environment in the form of oxyhaemoglobin complex by diffusion. The blood as it flows through the body, it transports the oxygen from the blood to the body tissues again by diffusion.
As a result, carbon dioxide that is exhaled from the body tissues is gradually taken by the haemoglobin of the blood in the form of carbamino-haemoglobin complex by diffusion. Soon, the blood exhales the carbon dioxide gas outside of the body through the external epidermis again by diffusion.
There are five arches/hearts in the body of the earthworm that pumps blood throughout the body and in doing so it transports oxygen to the body tissues and takes out the carbon dioxide gas respectively during the flow.
This is how the earthworm’s circulatory system helps them in breathing and respiration comfortably.