How To Tell If Mystery Snail Eggs Are Fertilized?

Disclosure: When you purchase something through my affiliate links, I earn a small commission. As an Amazon Associate, I earn from qualifying purchases.

I remember the excitement when I first saw a clutch of mystery snail eggs. As I wanted to raise them, the first question that popped into my mind was whether the eggs were fertilized. Luckily, over the years, I gained a lot of experience in this field.

Fertilized mystery snail eggs will darken towards the end of the first week and become irregular in shape. On the other hand, unfertilized eggs will remain pink, small, and uniform in size.

As we move forward, I will elaborate on the differences between fertilized and unfertilized mystery snail eggs and include some useful pictures for a better understanding. I will also discuss what to do with unfertilized eggs and what it means when they become white.

Still curious? Feel free to check my complete guide on mystery snail eggs. There, I discussed how to care for the eggs, what their stages are, how to tell if they are fertilized, and much more

How To Tell If Mystery Snail Eggs Are Fertilized?

You can’t rear mystery snails if the eggs are dead. Fortunately, differentiating between fertile and infertile eggs is not as difficult as people think. Look out for the following:

1. Fertilized Eggs Will Change Over Time

Have you looked at the eggs? If you observe them closely, you will notice tangible changes in their appearance. The cluster is soft and pink at the start. But over the next 24 – 48 hours, it will harden.

The colors will also grow darker with each passing day. As the gestation period nears its end, the eggs will adopt a slimy texture. They are also irregular in shape.[1] 

Dead eggs are the opposite. They are small, pink, and uniform in size. You won’t notice the black spots that fertilized eggs develop.

2. Fertilized Eggs Should Hatch Within Three Weeks

How can you tell whether or not a mystery snail egg is dead? The first answer is the most obvious. A fertile egg will hatch. 

Naturally, mystery snail eggs require a conducive environment with temperatures of 75 to 78 degrees F and humid conditions.

A cluster of eggs in the appropriate environment will hatch in two to three weeks unless the clutch detaches from its surface and the embryos down. You can’t ask for more tangible proof than this.

Some aquarists have thrown seemingly dead eggs away, only for the eggs to hatch in the bin. However, those scenarios shouldn’t encourage you to delay. 

You cannot wait indefinitely. Dead eggs will rot. If they sink below the waterline, the decomposition process will cause the ammonia concentration to spike.

Therefore, you should remove eggs that have failed to hatch after 14 days, especially if the color and size remain unchanged. At the very least, keep them in a separate container away from the community tank.

Bear in mind that not all fertilized eggs eventually hatch. As I previously discussed, mystery snails lay between 50 to 500 eggs in a single batch, of which merely 20 to 40 will eventually hatch.

Unfertilized mystery snail eggs will remain pinkish and small, as in the picture.

3. There Must Be Male And Female Interaction

Do you have any male snails in the tank? A female snail can lay eggs in the absence of a male.[2] However, the eggs are not viable because the female snail did not mate with its male counterparts. 

Therefore, if you don’t have male snails in the tank, you shouldn’t bother checking the eggs for signs of fertility. They are all dead, without question. 

Admittedly, mystery snails can store sperm for over a hundred days. They can fertilize their eggs months after mating with a male snail, even though their current tank doesn’t have any males.

But if your female snails were born in the aquarium, you know for a fact that they can’t produce fertile eggs because they’ve never mated with a male. 

Have you noticed male mystery snails in the aquatic space? Differentiating the genders in this species is easier said than done. Female snails are easier to spot, but only during breeding because their shells become translucent.[3]

Additionally, male snails have a penis sheath.[4] But you have to lift the snail to find it. Apple snails have similar physical attributes.

You can also look at the shell. Male snails have a rounder opening in the shell because the penis has to extend through the hole when the creature mates.

Again, the snail’s origins matter. A female snail you bought from the store can still produce fertile eggs even though the aquarium doesn’t have male snails.

A great video showing the differences between male and female mystery snails.

4. The Paper Towel Test

This test is a little inconvenient because you must place the eggs on a white paper towel. If you notice red stains on the towel, the eggs are dead. Fertile eggs do not leave stains.[5]

5. Unfertilized Eggs Develop A Terrible Smell

Some people have never reared mystery snails. Therefore, they cannot tell whether or not the egg cluster is changing color. 

Others have thrown seemingly dead eggs away only for the offspring to hatch in the trash. The only surefire attribute that identifies dead mystery snail eggs is the smell.

Unfertilized eggs will develop a terrible smell after a few weeks. That is as good a time as any to throw them away. 

What To Do With Unfertilized Mystery Snail Eggs?

Get rid of them. They don’t serve any purpose. You can’t leave them in the aquarium. They will ruin the water’s chemical balance once they decompose. Eventually, the smell will become a nuisance. 

The best option is to freeze the eggs before crushing them and throwing the remains in a bin or flushing them down the toilet. Usually, the toilet option is frowned upon, but only where viable eggs are concerned.

If they hatch, the mystery snails could wreak havoc on the local flora and fauna. But dead eggs cannot hatch. Technically speaking, they are not a threat. 

You could always feed the eggs to fish. They will eat anything that fits in their mouths. Just make sure to remove the eggs your fish ignore.

For more information on this topic, feel free to check this article, where I discussed what you could do with mystery snail eggs. You’ll find all the answers there, whether you wish to raise the eggs or get rid of them.

Unfertilized mystery snail eggs will remain pink and small in size.

Do Mystery Snails Lay Unfertilized Eggs?

Yes, mystery snails lay unfertilized eggs. According to some studies, reproductive factors like the number of eggs will vary in response to variables like the presence of predators.[6]

However, if the female mystery snail has not mated with a male snail, it will produce unfertilized eggs regardless of the circumstances. But even if you have a male snail in the aquarium, the female can still lay unfertilized eggs.

The numbers matter. The more snails you have, the more fertile eggs you will get. Fewer snails turn the breeding process into a gamble.

Why Do Mystery Snail Eggs Turn White?

White is a confusing color. You expect mystery snail eggs to transition from pink to dark brown over the days and weeks. In that regard, it is easy to blame the white color on mold.

And in some cases, white mold can manifest on the surface.[7] However, in other cases, the color is a sign of maturity.

The eggs may turn white because they are on the verge of hatching, especially if they develop a slimy texture. The presence of mold shouldn’t frighten you.

It simply shows that the snails are eating their way out of the egg. But again, white eggs are confusing because this color can also signify trouble. 

For instance, if your eggs are not only white but brittle, something has gone wrong. You don’t have enough humidity. As a result, the eggs are drying out. Don’t be so quick to discard the eggs. 

Some aquarists have successfully hatched the eggs by tapping them with a toothpick to break them, allowing the offspring to emerge.

If all that confused you, here is a table that will simplify things:

White & slimy textureThe eggs are about to hatch
Whitish & brittleDried eggs that won’t hatch
White & terrible smellInfertile, rotten eggs

What Should I Do With Fertilized Mystery Snail Eggs?

Fortunately, you don’t have to do much. If the environment was comfortable enough for the mystery snail to lay the eggs, it is also good enough for the eggs to hatch.

Some aquarists keep the eggs in a damp cloth for several days. That could be a good idea because it keeps the eggs safe. But some of the eggs will break during the transfer.

I personally prefer leaving the eggs attached to the aquarium’s wall. All you have to do is to follow the eggs and make sure they don’t fall into the water.

Also, when making a water change, make sure you leave a gap of about 0.5 inches between the water line and the lowest eggs in the clutch. That will prevent the eggs from drying out.

If you found this article helpful, these may also interest you:


If a week has passed and your mystery snail eggs haven’t changed, they are probably unfertilized. In this case, they will remain small, pink, and their shape will be uniform.

However, if the eggs go darker as time passes, the eggs are fertilized and will hatch within the following weeks. It will seem as if the eggs develop mold, but that is merely the baby snail growing inside.

Unfertilized eggs will also smell after the first week. That is a sign you should take them out, as they have rotten and will not hatch.