Why Do Snails Turn Green? The Fascinating Green Metamorphosis

Why Do Snails Turn Green

Why Do Snails Turn Green? The Fascinating Green Metamorphosis

Have you ever noticed that some snails, like mystery snails, can have a range of captivating shell colors? It’s fascinating how these tiny creatures can exhibit golden, brown, or even black stripes on their shells, adding to their charm. But what happens when your snails turn green? Should you be concerned?

Snails turn green because they become adorned with jackets made of green algae. These jackets, formed by the rapid growth of the notorious green hair algae, can transform the shells of snails into a vibrant shade of green. The change in color itself is not necessarily a cause for immediate alarm.

The notion of snails turning green can be concerning for many hobbyists and aquarists. This article aims to delve into the reasons behind this phenomenon and provide guidance on how to reverse the process.

Green Snails: A Tale of Snails Adorned in Emerald Shells

Green Snails on Rraiatea Rreef
Turbo marmorartus ©Living Oceans Foundation

As we embark on our quest to unravel the mystery of snails turning green, we must acquaint ourselves with the existence of the enigmatic green snails.

Alison Barrat and Alexandra Dempsey, two passionate enthusiasts, set out to explore the history of green snails, affectionately referring to them as “valuable aliens.”

In their captivating article, they argue that green snails hold a significant place in the annals of snail history, despite their introduction into different ecosystems being an epic scientific failure.

The story of green snails traces back to 1967 when a group of scientists deliberately introduced 42 of these snails to a single reef in the southern coastal region of Tahiti. Originating from the Indo-Pacific, these snails bore the scientific name Turbo marmorartus.

The lush and inviting waters of the southern coastal area of Tahiti provided the perfect breeding ground for these green snails, allowing them to thrive and eventually dominate the ecosystem.

The purpose behind introducing these green snails to the south coast of Tahiti remains an intriguing puzzle. The scientists envisioned these snails as a valuable addition to the new ecosystem, with the potential for lucrative returns by selling their meat and shells.

Initially, the snails proliferated in the south coast region of Tahiti, satisfying the scientists. However, their population numbers were still insufficient to yield a profitable harvest.

The scientists closely monitored the snails, mainly focusing on their population growth. After three years, the scientists conducted the first snail census, revealing the dominance of the green snails along the east coast of Tahiti.

Curiously, none migrated to the west coast, leaving the scientists puzzled by their selective behavior. Determined to understand this phenomenon, they continued introducing the snails to different ecosystems.

In the 1990s, the green snails were transported to the remote islands of Tahiti, which turned out to be a pivotal move. This decision led to the opening of the first fishery in 1993.

Within the same year, the scientists conducted their inaugural harvest, yielding an astounding haul of over 53,000 Green Snails. This remarkable catch was estimated to be worth a staggering one million US dollars!

The commercial potential of the green snails attracted a wave of business enthusiasts to the coastal region of Tahiti, anticipating an explosion in the snail population. However, their expectations were proven wrong.

While the scientists dedicated themselves to expanding the green snail population, poachers had their eyes on the prize. Regrettably, the scientists lost over 40,000 snails to these illegal activities.

Nonetheless, they persisted and introduced the green snails to ten additional locations on eastern Tuamotu Island in 1996. Each location received a hundred snails.

With about 1,000 snails distributed across these ten new areas, the scientists anticipated a substantial multiplication and a bountiful harvest. However, nature had other plans, as the snails did not thrive as expected, particularly compared to the success of the initial population.

A green snail census in 1998 yielded unexpected results, as the scientists failed to find a single living snail in the ten new reefs on Tuamotu Island. The presence of broken shells was the only evidence suggesting the snails had been present, indicating a predator that had a feast at their expense.

In 2000, the fishery managed to catch approximately 3,000 snails, but since then, the snails have all but disappeared. The history of the green snails in the coastal area of Tahiti represents a 45-year scientific endeavor marked by the natural and controlled dispersal of the animals and, ultimately, an epic failure.

The scientists speculate the following:

  • The locals may have unofficially relocated the snails.
  • The snails’ larvae may have been swept downstream by powerful ocean currents.
  • Predators might have preyed upon the snails.

The Mystery of Beautiful Brown Snails Turning Green

Turban Snail
Turban Snail ©New Scientist

By now, you are aware that your mystery snail does not belong to the Turbo marmorartus species. However, if its once-brown shell has taken on a green hue, there must be a compelling reason behind it, and we are here to unravel the mystery.

In the wild, snails can undergo a color transformation to green as a protective measure against the scorching sun. Scientists explain that the newfound green color on the snail’s back acts as a shield, minimizing the direct impact of sunlight on the shell.

This color change is believed to be a direct response to the challenging environmental conditions found in beach habitats. The turban snail is often associated with this intriguing green jacket phenomenon.

Typically inhabiting rocky shorelines, these snails actively feed on algae, allowing it to grow on their shells, eventually resulting in a complete covering of green-colored mats.

Therefore, when your snail turns green, it is likely wearing a protective jacket in the form of algae, providing it with added defense against the elements.

Snails Turning Green in Aquariums

While snails in the wild allow algae to grow on their shells for sun protection, the phenomenon of snails turning green in a controlled environment, such as an aquarium, poses an interesting question.

To shed light on this matter, let’s turn to the experience of a dedicated snail enthusiast. This aquarist maintains a harmonious setting in a ten-gallon (38-liter) aquarium housing goldfish and two tiny snails.

However, a significant development occurred when the snails unexpectedly turned green. This alteration in their shell color raises multiple potential explanations.

Notably, the snails’ recent green transformation, distinct from their past appearances, suggests that there may be more at play than mere algae growth on their shells. A particular species of persistent algae, known as blanket weed, could be the culprit behind this change.

Blanket weed tends to attach itself to any available surface, including the shells of moving snails. Alterations in aquarium lighting, such as changes in the number of hours the lights remain on or the installation of new light bulbs, can promote the growth of this stubborn algae.

Moreover, fluctuations in nitrate levels within the aquarium could also contribute to the proliferation of blanket weed algae. If the nitrate concentration exceeds 10 parts per million, it creates an ideal environment for the growth of this algae species.

Aquarists should remain vigilant in monitoring lighting conditions and nitrate levels to prevent the unwanted spread of blanket weed algae, which can lead to the green appearance of snails in the aquarium.

What Should You Do When Your Snails Turn Green?

To determine whether the lighting conditions are responsible for your snails turning green, do the following:

  • Closely monitor the duration of time the lights are kept on.
  • If lighting is not the issue, pay careful attention to the water parameters and ensure they are maintained at optimal levels for the well-being of fish and snails.

Regarding the green coating on your snails’ shells, you can consider using algae-removing chemicals such as API ALGAEFIX Algae Control. However, DO NOT use these chemicals if your goldfish share the same tank. While these chemicals are effective in removing algae, they can be harmful to goldfish.

Alternatively, you can transfer the snails to a separate container away from any light source for approximately two weeks. During this period, provide them with a specialized fish-based diet.

An inadequate food supply may encourage the snails to consume the algae coating on each other’s shells. This method can effectively address the issue of growing algae without using chemicals that could potentially harm the shells in the process.


For enthusiasts of snails, these fascinating creatures possess an inherent beauty that captivates their admirers. Therefore, any deviation from their usual appearance sparks curiosity and concern.

This article has shed light on the phenomenon of snails turning green, attributing it to the attachment of algae to their shells, forming a green mat. It is important to note that the snail’s shell itself does not change color; instead, it appears green due to the presence of algae.

The recommended solution is to remove the algae and maintain optimal aquarium conditions to prevent a recurrence of the issue.



  • Paul Odoteh

    Paul Odoteh is an established writer and editor with nearly 10 years of experience in writing and editing. He holds a bachelor's degree in IT and has written for numerous publications and individuals. Currently, Odoteh is dedicated to expanding his blog, SnailPedia.com, which was inspired by his passion for owning an aquarium.

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