Asexual reproduction isn’t possible because all eggs laid without mating with a male will be unfertilized. Even if no mating has occurred, the egg will still form and be laid. The eggs can’t be reabsorbed.
The likelihood of fertility (even if mating has taken place) depends on the diet and health of the female. Also, the incubation temperature and humidity level will determine if tortoise eggs will hatch.
To determine if the eggs are fertile, you can use candling. This involves shining a light on the egg to see the embryo inside. After a few days of incubation, the color will tell you if the eggs are fertilized.
How Do Tortoises Fertilize Their Eggs?
Once mating occurs, the male’s semen travels to the female’s ova. The fertile ovum then travels to the oviduct tube, where the egg white is formed to protect the ovum.
The shell membrane begins to form in the shell gland. The shell pores are closed just before the egg is expelled due to a protective layer called the bloom. The entire shell is intended to keep bacteria out and the ovum from drying as the embryo develops.
A single mating session can keep a female tortoise producing fertile eggs for about 4 years.
According to Molecular and Cellular Probes, a single clutch of tortoise eggs can have multiple paternity due to how female tortoises store sperm and fertilize eggs.
A female tortoise will lay 4-30 eggs per clutch, depending on the species.
According to the American Journal of Anatomy, sperm is reserved in a female tortoise’s oviductal lumen and endometrial glands. However, the longer it stays there, the less fertile the eggs become.
How To Know If Tortoise Eggs Are Fertile?
The most effective way to determine if a tortoise egg is fertile is through candling, which involves shining a bright light on the egg to see the contents inside.
You may be unable to distinguish a fertile egg from an infertile egg in the first few hours after the tortoise lays them. You can begin candling them after 2-3 days, as you’ll be able to see the signs of a fertile egg.
There are things to look out for when candling eggs, such as:
Color
A fertilized egg will be red or pink, but you may not see the embryo yet.
Because the ovum was fertilized in the tortoise’s oviduct tube, the egg will be full of blood vessels needed to ensure the baby tortoise grows properly.
Veins
The veins usually appear 5-7 days after the female tortoise has laid the eggs. They begin from the top and bottom and slowly move toward the center of the egg after a few days.
Embryo
The embryo starts as a small dot in the center of the egg. As the baby tortoise develops, it’ll grow until you can’t see what’s inside anymore, as the baby will have filled the entire egg.
As the days pass and the baby tortoise develops, you may see it moving inside the egg when candling.
Chalking
‘Chalking’ on a tortoise egg refers to the whitening of the egg.
It’s the first stage of egg development, and it occurs 2 days after the female has laid her eggs. When tortoises first lay their eggs, they’re pink or red, but they slowly turn white and chalky over time.
When an egg begins to chalk, you’ll notice white patches on the egg. The white patches will multiply and spread until the egg is whiter and stronger than when the female first laid it.
Beware of mold, which can look like ‘chalking.’ If an egg is moldy, this may spread to healthy eggs. If you’re unsure if the eggs are ‘chalking’ or moldy, take a picture and ask a vet.
How To Candle A Tortoise Egg
Once embryonic development has begun, it’s important not to change the orientation. Under no circumstances should you shake or turn the eggs over.
To candle a tortoise egg properly, you’ll need a dark room and a flashlight for candling. If you’re candling the eggs often, remove them from the nest.
According to Zoo Biology, the tortoise will only feel territorial over her eggs for about 2-3 days. So, once she lets you take the eggs, you can place them in an incubation box for monitoring.
That’s so you don’t have to pick them up when candling. When you pick up tortoise eggs, if you don’t keep them in the same position all the time, you risk drowning the embryo.
Also, you may accidentally detach the embryo from the shell, effectively killing the baby tortoise.
Close the blinds/curtains and door, and turn off the lights. Buying a candling flashlight is better than using a regular flashlight because it’s smaller, making it easier to press against the egg.
Candling flashlights have a stronger light, allowing you to see through darker eggs. It’s best not to disturb the eggs too much, so only candle them every 3-4 days.
How Long Does It Take for A Tortoise Egg to Hatch?
How long it takes for tortoise eggs to hatch depends on the species. Different species will have different incubation periods and phases, so learn as you can about the species you own.
Take a look at the chart below to find out when your tortoise’s eggs will hatch:
| Tortoise Species | Incubation Period |
| Sulcata Tortoise | 100-120 days |
| Russian Tortoise | 56-70 days |
| Leopard Tortoise | 8-15 months |
| Red-Footed Tortoise | 115-150 days |
| Hermann’s Tortoise | 53-70 days |
| Horsefield Tortoise | 50-100 days |
| Indian Star Tortoise | 86-100 days |
While it’s tempting to crack the egg to help a baby tortoise emerge, it has some drawbacks.
It’s difficult to know if the eggs are late hatching, and something may be seriously wrong with them regardless. For example, anoxia (insufficient oxygen to support normal cellular function).
How To Help Tortoise Eggs Hatch Successfully
If tortoise eggs are to hatch, they must be incubated at the optimal temperature and humidity level.
If the temperature is too low, the eggs will develop slowly or not at all. Similarly, if the temperature is set too low, it’s more likely that hatchlings will arrive with physical deformities.
The advised incubation temperature is between 30 and 31.5 degrees centigrade, which should be verified with an accurate thermometer or thermostat.
This temperature range is proven to result in both sexes. Environmental Sex Determination (ESD) means that elevated temperatures lead to females and lower temperatures lead to males.
The optimal humidity level is species-specific, but 80% is usually optimal. These conditions can be met by placing the eggs on moistened sphagnum moss or vermiculite.
