Why Do Snails Turn Black?

Why Do Snails Turn Black

Why Do Snails Turn Black?

Snails stand out as tiny, slow-moving creatures adorned with remarkable shells. These shells boast mesmerizing hues and intricate patterns that define the uniqueness of each snail population. But have you ever wondered why some snails undergo a fascinating transformation, turning from their original colorful glory to a striking shade of black?

Snails turn black because of several factors. These include the snail’s genetic makeup, camouflage purposes, food deposits such as the overgrowth of black-headed algae on the shell, and imbalances in its aquatic environment, such as changes in water pH, nitrite, and ammonia levels.

Even though snails naturally undergo changes in their shell colors over time, excessive blackening can become a cause for concern. This article delves into the intriguing phenomenon of blackening in snails and explores its potential implications.

Genetically Influenced Blackness: The Case of Black Mystery Snail

B-Grade Black Mystery Snails
Image Source: Aquatic Arts

The color and pattern of a snail’s shell are determined by its genetic makeup, which means that some snails naturally have a black appearance, and there is no cause for concern. One example of a naturally black snail is the Black Mystery Snail.

Black Mystery Snails are often mistaken for Apple Snails, but they differ. The primary distinguishing feature between Apple Snails and Black Mystery Snails is the size of their siphons.

Black Mystery Snails have a significantly longer siphon, which allows them to breathe underwater. These aquatic snails spend selective periods of the day submerged in water, using their long siphons to breathe without needing to come to the surface.

Black Mystery Snails are highly favored by snail enthusiasts and aquarists. They are often kept for their aesthetic appeal, as their colorful shells add a touch of elegance to an aquarium.

Interestingly, Black Mystery Snails come in various colors, including:

  • Ivory black
  • Golden black
  • Jet black

Some individuals of the same species exhibit black shells with tan striping, while others have a more purple hue with gray stripes. The intermingling of these varieties has resulted in a sub-species of the Black Mystery Snail with a golden black shell adorned with purple stripes.

This particular variation has become highly sought after by aquarists and snail enthusiasts, perhaps due to the regal association with the color purple. The black coloration in these snails is not a cause for concern, and identifying the species of a snail can be quite useful.

The Protective Form of Blackness in Snails

The color change observed in snails is often directly linked to their need to remain inconspicuous. Being slow-moving creatures, snails face a significant disadvantage in an ecosystem with various types of animals.

Scientists have concluded that the color of a snail’s shell plays a crucial role in staying hidden from predators, particularly birds of prey like song thrushes, known for their selective prey choices. Birds of prey tend to target snails based on the most common color, making snails with rare colors more likely to evade predation.

In the Nottingham study by Dr. Davison and Hannah Jackson, snails were categorized based on color. Initially, the Ph.D. students categorized the snails using their naked eye, and later they employed a specially designed machine that directly illuminated the snails.

This machine also produced various light spectrums to illuminate the snail shells. Through their observations using the machine, Dr. Davison and Hannah Jackson discovered snails with the following colored shells:

  • Pink
  • Brown
  • Yellow-colored

The categorization based on the naked eye and the spectrometer yielded significant differences, indicating that while the human eye accurately identified yellow-colored snails, it struggled to correctly identify pink or brown-colored snails. Dr. Davison and Hannah Jackson even disagreed on distinguishing between pink and brown shells.

The Nottingham study shed light on how a snail’s color can change as a primary camouflage. If even experts like Dr. Davison and Hannah Jackson struggled to differentiate between brown and purple snails, it suggests that birds of prey may fare even worse.

If you remain unconvinced, let us explore the findings of yet another study.

Color Polymorphism in Littorina sitkana

Color Polymorphism in Littorina sitkana
Image Source: Race Rocks Ecological Reserve

In 1999, Giovanni Rosso conducted a study in Race Rocks Ecological Reserve to explore the relationship between Littorina sitkana shell color and surrounding rocks. After several days of analysis, Rosso discovered a strong connection between the snail’s shell color and the color of the background substrate.

Snails with light-colored shells tended to inhabit areas near rocks that matched the color of their shells. In contrast, snails with black shells dominated regions with dark-colored rocks.

Interestingly, Rosso made significant findings within the same study. He observed a larger population of snails with black shells than white ones. Since the area was a marine protected area and people did not interfere with the existing wildlife, it could not be attributed to human interference in favor of white-shelled snails.

The only plausible explanation is that the smaller population of white-shelled snails results from excessive predation. The area with clear waters is dominated by white and black race rocks, making white-shelled snails easily identifiable in dry and wet conditions.

In contrast, snails with black shells residing among the dark-colored rocks thrive in larger populations due to their ability to remain hidden. The disadvantage of color exposes white-shelled snails to predators, while those with black shells remain unseen.  

Could Snail’s Color Change From Light to Dark an Issue of Maturity?

In certain snail species, the shells can darken as the snails mature. Previous studies have indicated that darker shell colors are influenced by genetics and mutations. Now, it is also recognized as a characteristic of the aging process.

Poor Water Quality and Black Shells

Mystery Snails exhibit a wide range of patterns and colors on their shells, including the following variations:

  • Gold
  • Yellow
  • Purple
  • Brown

However, if their shells start darkening, it could indicate poor water quality. Mystery Snails are sensitive to aquatic environments that contain toxic substances like:

  • Copper
  • Nitrite
  • Ammonia

Additionally, any fluctuations in water pH can impact the natural coloration of a snail’s shell.

Unlike other causes of shell blackening, changes resulting from poor water quality require immediate attention from snail keepers. Typically, the most immediate solution is to change the water.

Algae Infestation Can Cause Changes in Water Quality

Aquariums serve as human-created aquatic environments that undergo various uncontrollable changes. Aquarists often introduce snails as cleaners into these tanks, as they feed on algae, particularly those clinging to the aquarium walls.

Interestingly, black-headed algae present a unique challenge as they are the most difficult to remove from aquarium surfaces and tend to cling to surfaces like the shells of snails residing in the tank. As the algae multiply on the snail’s shell, an aquarist may mistakenly believe that their pet snails have changed their color to black due to the darkness of the algae.

Fortunately, the solution to this problem is relatively straightforward. By introducing different species of snails, particularly those that feed on black-headed algae, you can effectively clean the algae off the affected snails’ shells.

This serves as a gentle reminder of why some snails may appear to be attached to the backs of their fellow snails—they are simply feasting on the algae.


This article has examined several reasons why snails turn black, encompassing natural and unnatural causes. Natural causes include the aging process and evolutionary purposes, which can trigger changes in the snail’s shell color.

Furthermore, snails may change their shell color as camouflage, as exemplified by the Race Rocks Ecological Reserve study.

Lastly, snails can exhibit black shell coloration as a response to residing in unhealthy environments. This particular cause warrants concern and the solution lies in maintaining cleaner, well-balanced environments for the snails.



  • 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.

    https://www.snailpedia.com pdoteh@gmail.com Odoteh Paul

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