When you think of earthworms, the first thing that comes is their burrowing ability which helps with aeration and drainage in the soil. By doing so, they help maintain the soil’s fertility.
However, earthworms also have other anatomical features that set them apart from other worms. One is the thick saddle like ring found near the head end of their body wall called the clitellum.
In this article, we’ll take a closer look at the clitellum and its functions.
What is an Earthworm’s Clitellum?
The clitellum is an essential part of an earthworm’s reproductive system. Its main function is to store eggs, aid in reproduction, secrete fluid to form the cocoon for eggs, and create a viscid sac that encases the cocoons together.
What Is Meant by Clitellum?
Clitellum (plural: clitella) comes from the Latin word clitellae, which means packsaddle.
True to its meaning, the clitellum is a thickened band of tissue found in the epidermis encircling the earthworm’s body wall near the head.
This saddle like ring found towards a worm’s head (about one third down) varies in size and even in appearance among the different worm species.
What Is the Function of The Earthworm Clitellum?
Aid in Reproduction
Earthworms are hermaphrodites, meaning each worm possesses both male and female reproductive organs.
Although earthworms don’t have traditional sexual organs, they still need a mate to reproduce sexually, though many species can even reproduce asexually.
The clitellum facilitates this asexual or sexual reproduction process.
Earthworms mate by aligning themselves with each other and joining their clitella.
The worms exchange sperm as they lay side-by-side.
During copulation, the clitellum of each worm will also secrete mucus, a viscous fluid to keep them attached and paired together until the sperms have been exchanged.
Fun fact: Earthworms’ mating process can take up to around 24 hours.
Secrete Fluid to Form the Cocoon for Eggs
Once the earthworms are done exchanging sperms, the clitellum secretes a viscous fluid (mucus) to envelope the sperms.
When exposed to the air, the mucus hardens to form a cocoon around the sperm.
As the cocoon forms, the worms will inject and lay eggs into the cocoon to complete the fertilization process.
The earthworm’s eggs the clitellum secretes are then laid into the soil.
The cocoon protects the eggs from predators and harsh weather conditions.
Fun fact: Each earthworm cocoon can contain up to 5 worms. With this number, earthworms can easily double their population in 60 days.
Secrete Viscid Sac That Helps to Cement the Cocoons Together
The clitellum secretes a viscous fluid and secretes a viscid sac that encases the worm eggs all together in a larger protective layer.
This sac keeps the eggs moist and protected until they hatch, allowing them to develop in a safe environment.
It will then take around two weeks to two months for the eggs to hatch (species dependent).
After hatching, the young earthworms will burrow into the ground and begin to live on their own, from juvenile to mature worms.
Initially, it’s difficult to tell the tail end from the head end in juvenile worms. Maturation is complete when the swollen clitellum can be seen on the surface of the worms skin
(In some species of worm, the clitellum is not swollen like the Alabama Jumping Worm and Indian Blue Worms. Theirs is flush and has a light colored pigment – almost milky.)
Why Do All Earthworms Have a Clitellum?
The clitellum is an essential part of the reproductive system of sexually mature earthworms.
It indicates that the reproductive system of earthworm is ready and they are fully mature.
It starts to appear as a non-segmented swelling around the middle to top third of the worm body once they reach adulthood in about six to eight weeks.
Clitellum can be orange, reddish-brown, or white in color.
The clitellum is not species specific to earthworms as they are also found in other types of worms.
Most polychaetes (aquatic worms), for example, under the class Polychaeta, don’t have them but some do.
Where is the Clitellum Located on An Earthworm?
The clitellum of an earthworm is located near the anterior end of the earthworm’s body wall near the head.
It is a non-segmented section of the earthworm’s body usually found between the thirteenth and seventeenth segments.
How Many Segments Are Covered by the Clitellum?
The clitellum usually covers around three segments of an adult earthworm near the anterior part of the body.
Fun fact: An adult earthworm can be made up of 100 to 150 segments. This structure allows for the earthworm’s movement through the soil.
Can Earthworms Lose Their Clitellum?
Although clitellum is essential for reproduction, earthworms can lose it under certain conditions.
The clitellum atrophies and falls off if they experience a long drought season.
The clitellum will grow back once the conditions improve and they’ll be ready for asexual or sexual reproduction again.
Frequently Asked Questions About Earthworms
How Do You Know that an Earthworm Is Ready to Reproduce?
It takes about two months for hatched earthworms to develop into adults.
This is when they can produce eggs and sperm from their reproductive systems.
You will also know an earthworm has reached sexual maturity when you see the orange clitellum, according to one source. But this is largely species dependent.
Is the Clitellum the Same Size on Every Species of Earthworm?
No, though they have very distinct similarities, there are some differences.
Varying species of earthworm will have a clitellum that has a differing size, color, swelling and shape.
Indian Blue Worms Clitellum
The Indian Blues have a clitellum that is more flush with their body, rather than being a thickened glandular thing sticking out of that section of the body.
It is also closer to the head than clitellum’s on nightcrawlers or red wigglers.
It has a light colored pigment, compared to the rest of the body wall.
Red Wigglers Clitellum
Red wigglers have your typical thick, saddle like ring found towards the head section of the body (but very slightly lower down than the Indian blue).
The coloring is also more of a red-brown color.
NightCrawlers Clitellum
Nightcrawlers have a similarly obvious thickened glandular and non segmented clitellum to the red wigglers.
Their clitellums coloring can be less obvious, especially on the European Nightcrawler (Eisenia hortensis – or formerly classified as the Dendrobaena veneta), as they are reddish brown colored all over.
Alabama Jumping Worm’s Clitellum
Asian Jumping worms (or Alabama Jumpers) have a clitellum that is more gray or milky in color.
Similarly to the Indian Blue worm, it is smooth and flush, rather than raised above the body like Nightcrawlers.
Another difference from Nightcrawlers, is that their clitellum encircles the body entirely where as it only partially does on Nightcrawlers.
Summary
Earthworms are some of our planet’s most interesting creatures.
Sexually mature earthworms have a thickened glandular of non segmented tissue that encircles the worm’s body near the anterior/head end, called the clitellum.
While the main function of the clitellum is primarily to aid in reproduction and egg storage, it also plays an important role in the life cycle of the earthworm.
The clitellum secretes a viscous fluid to form a cocoon to protect the earthworm’s eggs from predators and harsh weather conditions.
Each cocoon contains several eggs, which hatch into new worms.
We hope you found this answer helpful and you learned more about this interesting organ.
Are there any fun facts about earthworms that you’d like to share with us?
Did you know worms use bristles called setae to move? Read more in our guide about how earthworms move
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