do worms have eyes

Do Worms Have Eyes? And Other Worm Wonders

Worm species play an important role in the earth's ecosystem. They're insects that breathe with their skin because they do not have lungs or noses. They do not perceive the world with simple eyes common to other animals. 

Yet, worms still survive. They eat, burrow, and mate without eyes. This article explains how worms detect light. It explores how they move around and the functions of their chemoreception abilities. We will also discuss five facts about a worm. 

Related Read: How To Start A Worm Farm For Vermicomposting At Home.

Do worms have eyes?

worm close up
Photo by Thomas Brown on Wikimedia Commons licensed under CC BY 2.0 (Cropped from original).

Worms move underground quite efficiently. It begs the question, do worms have eyes for navigation? The answer is no. 

Worms do not have the visual organs common to most animals, including humans. They navigate their environment expertly with their other senses. 

Worms have cells known as receptors on their bodies. They use these receptors to sense whether it is dark or light. It helps worms detect if they are underground or above ground. 

How do worms detect light?

worm on grass
Photo by sarahharding on Needpix (Public Domain).

Worms have light receptors used to sense light. These receptors are within its dorsal section. Earthworms have sensory receptors around the epidermis and dermis regions on the prostomium. Each light sensor is connected by nerves running through the worm’s body.

These form light-sensitive areas around their body, alerting them of their position above ground. However, earthworms are barely above ground. So, these receptors also serve as a warming system to alert them of predators and other potential dangers. 

A worm’s body reacts to visible lights, especially when the exposure is sudden. It may also disrupt their ability to move. Research shows that ultraviolet light might be harmful to earthworms. The ultraviolet light after rainfall could be why some earthworms die1 on the earth’s surface.

Worms react to various wavelengths of light. They function under blue light but lay dormant under a red light. Most researchers find it easier to study earthworms under red light. Research shows that a worm's ability to detect light is connected and made possible by the cerebral ganglia. 

The cerebral ganglion is a little brain above the earthworm’s pharynx and connected to the first ventral ganglion. Light intensity passes over the axons, connecting two hemispheres of the cerebral ganglia and the ventral side.

Worms feel weak light intensity when the stimuli reach their muscles through the brain to the cerebral nerves or the pharynx nerves. They respond negatively to weak light intensity by contracting their muscles.

Do worms need eyes?

worm on rock
Photo by Ivan Ivanovič on Unsplash.

People ask if worms have eyes that work like human eyes because they live efficiently within the soil. Worms live and eat organic matter in the soil. They mostly live alone, traveling their environment or digging a permanent burrow. 

We reckon worms don't need eyes because they have sensory receptors and other sense organs that help them navigate the dark soil efficiently. Other sense organs apart from the sensory receptors help an earthworm survive in the soil and on the surface. 

Worms have chemosensors, a sensory organ that helps sense and react to chemical stimuli. Research conducted by Darwin showed that earthworms can differentiate between the food they eat. Some worm species have a range of chemical stimuli2, while others can detect a few chemicals3.

An earthworm's chemical reaction helps it select a safe food and sense dangerous environmental conditions like soil acidity. It helps a worm detect the mucous secretions of other worms during the mating season. 

The chemoreceptors are on the prostomium. It is a fleshy covering for the worm's mouth or the lining in the mouth's inner surface. These are the areas of the worm's body making contact with the environment.  

A study on worms’ food preferences showed worms prefer leaves with low polyphenol content. Another study conducted by Edward and Heath demonstrated this by feeding them oak leaves. The results showed that worms preferred the oak leaves with washed-out phenols. 

Furthermore, earthworms avoid alkaloids in materials above a specific concentration. They react to glucose and saccharose inconsistently. They can detect all forms of acid. High concentrations of citric, malic, phosphoric, tartaric, and oxalic acids in plant materials affect worms adversely.

How do earthworms move?

earthworm on a leaf
Photo by Gilles San Martin on Wikimedia Commons licensed under CC BY-SA 2.0 (Cropped from original).

Now that we've examined how a worm makes sense of the world. Let us examine how it transports itself to various parts of the earth. 

Worms must move into the soil to protect themselves from visible light and predators, find food, and mate. They dig through the soil with coordinated contractions of the longitudinal and circular muscles on the body wall. The muscle contractions are possible because the parts contain coelomic fluid. These segments keep the liquid from moving around because it would be difficult for an earthworm to connect its ends for expansion. 

A worm uses its prostomium to find cavities suitable for burrowing. Then, it protrudes the setae on its posterior segments to keep it stationary on the ground. Its exterior segments extend forward as it contracts the circular muscles on the front end of its body.

The muscular contractions pass through the rings of the earthworm's body, causing contractions along the muscles of the ventral area. The concentration draws the rear end of the body forward. They repeat this process until they decide not to move anymore. However, the length of their extension depends on the pressure applied on the anterior end and the stagnant fluid’s pressure on the worm.

5 Facts About A Worm’s Body

Learn more about these creatures through our post on worm facts. In the meantime, here are some exciting tidbits about these creatures.

  1. Worms have a mouth on their head. It doesn't have eyes, arms, or legs. 
  2. Worms have the ability to repair their injured bodies.
  3. A worm cut in two does not result in two worms. The head end might survive and regenerate its tail, but the original tail section, though it may wriggle for a bit, will eventually perish.
  4. Worms are hermaphrodites. This means each worm carries both male and female reproductive organs, yet they still require another worm for successful reproduction.
  5. A worm has five hearts, providing sufficient circulation.

Conclusion: Do Worms Have Eyes?

Worms are unique insects necessary for the survival of the ecosystem. They maintain the soil health and facilitate good agricultural harvest. They also serve as food for other animals in the ecosystem. 

Worms perform these functions without eyes. They decompose organic waste in your garden with their sensory receptors and chemoreceptors. These senses help direct their body seat from light and dangerous animals. 

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1

Edwards, C. A., & Bohlen, P. J. (2022). Biology and Ecology of Earthworms. In Springer eBooks.

2

Edwards, C. A., & Bohlen, P. J. (2022). Biology and Ecology of Earthworms. In Springer eBooks.

3

Edwards, C. A., & Bohlen, P. J. (2022). Biology and Ecology of Earthworms. In Springer eBooks.

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