A lot of the coolest animals out there are reptiles. Turtles, lizards, crocodiles, and snakes are all varieties of reptiles that everyone loves to learn about. However, do reptiles lay eggs, or do they give birth to live young?
Most reptiles lay eggs. However, certain reptiles, such as boa constrictors, give live birth instead. Laying eggs allows the mother freedom while still giving the embryo inside some protection from dangerous predators in the form of a useful shell. It also allows them to have more children at once.
However, there’s a lot more to the story of reptile eggs than that, like the differences between egg-laying reptiles and birth-giving reptiles, and a certain reptile that has a really cool way of reproducing.
Why Do Reptiles Lay Eggs?
Scientists call reproduction via eggs oviparous reproduction. Ova is the Latin root for egg, while parous comes from a Latin stem meaning “to bring forth.” This means that oviparous animals “bring forth eggs.”
The primary advantage that being oviparous gives to animals is that an animal can lay many eggs at once. This means that it is more likely that one of those children will survive to adulthood. The other big advantage granted by egg-laying is that the mother of the eggs doesn’t need to constantly attend to them in order to keep them healthy and ensure that they survive. (Source)
The larger an animal is, the fewer advantages laying an egg has. This is because very large eggs are structurally easier to break and have more nutrients for predators that are looking for a meal. Since reptile eggs need to be big enough that the baby still fits inside until it’s ready to hatch, larger reptiles need to lay larger, inconvenient eggs.
At the same time, laying eggs has a bigger advantage for lighter animals or animals that rely on maneuverability to survive. This is because pregnancy involves having another animal grow inside the mother, which can both make the mother sick and make it harder for them to get around. Though a huge reptile such as a crocodile might hatch from a smaller egg than you might think.
While many reptile mothers, like crocodiles, do attend to their eggs to protect them from predators, others, like sea turtles, simply bury their eggs and leave. This protects the eggs from potential predators and allows the mothers to live normally and return to their homes.
Are Reptile Eggs Different From Bird Eggs?
Unlike the chicken eggs you’d pick from a grocery store, reptiles usually have oblong eggs with soft, leathery shells. Different kinds of reptiles have different shapes of eggs. While some snakes have eggs that are shaped like a very large grain of rice, turtle eggs are almost perfectly round.
Lizard eggs are roughly the same shape as snake eggs, but they are much smaller. Because lizard embryos attach themselves to one side of their egg, flipping them over can accidentally kill them. Because of this, it’s a bad idea to examine lizard eggs closely unless you are an expert.
Reptile eggs are very delicate, and moving them around too much can damage the embryo inside. Because of this, it’s important not to touch reptile eggs when you find them, even if you want to know what they are. Instead, you should call an expert if they need to be moved, or leave them alone if they don’t. Many experts don’t touch snake eggs until they have had time to develop so they can avoid damaging the embryo.
Reptiles don’t need to sit on their eggs to keep them warm. Reptiles instead rely on heat from the sun, the earth, or nearby vegetation to keep their eggs from freezing, allowing the parents to do other things while waiting for the egg to hatch.
How hard the eggs often depends on how much water they’re supposed to be able to absorb. As a rule, softer-shelled eggs are supposed to be able to take on some water, while harder eggs are made to keep water out.
Where Do Reptiles Lay Their Eggs?
Aside from one specific species of freshwater turtle in Northern Australia, all reptiles lay their eggs on land. Some will just lay them on the ground, while others will dig a little cave to keep them in, and others will bury their eggs and wait for the babies to dig back up to the surface.
This is because the embryo inside of an egg will die if it is submerged completely in water. Since eggs need to be able to take oxygen out of the air to distribute it to the growing embryo inside, submersion in water will drown the egg just like it would an animal.
Generally, reptiles prefer to lay their eggs in a warm, damp place where they will be difficult to find. Some snakes, limited by their lack of limbs, will lay their eggs in the first hole they can find. Many kinds of lizards dig their own hole to lay their eggs in.
Crocodilians are the only commonly known species of reptiles to protect their eggs after laying them in the wild. Because of this, they like to build their nest near their hunting ground, so if they need to leave it to get the food, they aren’t too far away.
Turtles, meanwhile, are famous for burying their eggs on beaches and then going back to the ocean. However they take precautions to protect their eggs, as they bury them far enough away from the ocean that they won’t drown or be washed away by waves, and the eggs are buried deep in the ground so predators can’t easily dig them up.
When Do Reptiles Lay Eggs?
Reptiles like to lay eggs in spring. While the exact time of year that they like to lay their eggs varies based on the species and the individual, this is the general period of time that they prefer.
The number of eggs they lay also differs significantly based on the species. While many lizards will only lay two or three clutches of four to eight eggs, some can lay up to fifty in a single clutch.
Since reptiles lay their eggs in the spring and have a thirty to sixty day gestation period, the new baby reptiles should show up in early summer, just in time to take advantage of reasonable bug population spikes.
While you might expect reptiles that give live birth to have fewer children at once, garter snakes can actually have between ten and forty babies at a time, which is kind of unfortunate for them. Boa constrictors, on the other hand, can give birth to up to sixty live babies at once.
Fortunately, they are very small babies and the boa constrictors are very big, so it doesn’t necessarily affect their movement very much.
Sea turtles, on the other hand, can lay up to one hundred eggs in a nest and may produce between two and eight nests in a season. This is a lot of eggs! Luckily, they don’t have to work to feed all of these children, which is likely a relief for sea turtle mothers. (Source)
What Reptiles Give Live Birth?
Animals that have live birth are called viviparous animals. In Latin, this means “to bring forth life.” Only a few reptiles don’t lay eggs. These reptiles are all either lizards or snakes. These species are few and far between, as the trait of being viviparous had to evolve in them independently of its evolution in mammals. (Source)
All boa constrictors are viviparous. This allows boa constrictors to be born at a much larger size than they would usually hatch from an egg. Since boa constrictors are some of the largest snakes in the world, this is probably very useful to them.
Some of the smallest snakes in the world are also viviparous! The North American Garter snake gives live birth. However, garter snakes aren’t technically viviparous. Garter snakes still produce eggs, they are just stored in the mother’s body until they are ready to hatch. Then, the garter snake gives birth to the newly hatched babies.
Animals like garter snakes that are both oviparous and viviparous (meaning that they produce eggs and give live birth) are called ovoviviparous animals.
Like garter snakes, skinks are very small reptiles that give live birth. However, only a few types of skinks are viviparous. These are Solomon Island skinks, which can be found in the Solomon Islands and Papua New Guinea, Blue-tongued skinks, which can be found in Australia, New Guinea, and Tasmania, and the shingleback lizard, which is native to western Australia.
Finally, the Jackson chameleon of Kenya gives live birth. This chameleon is notable for its three triceratops-like horns and their ability to focus its eyes in two directions at once.
What Other Differences Do Oviparous And Viviparous Animals Have?
While the biggest difference between these two categories is fairly obvious (one lays eggs, the other doesn’t) there is another difference that many scientists believe helps to determine whether a species is able to give live birth or has to lay eggs.
This difference has to do with how sex is determined during development. In animals that give live birth, sex is determined through genetic inheritance. However, in species that lay eggs, sex is usually determined by the temperature at which the egg is incubated.
Because of this, animals that lay eggs will usually keep them in places where different eggs will spend time in different ambient temperatures. Sand, for instance, doesn’t evenly distribute heat throughout turtle eggs, which means that the eggs will have a fairly even distribution of sexes.
The inside of a mother, however, tends to have a relatively consistent temperature, with all of the children developed inside of the same mother being grown at the same temperature. If these embryos had their sex determined by their temperature during gestation, they would all likely have the same sex.
If all the mothers in an area were about the same temperature, this could lead to the extinction of the species, as they may only have children of one sex.
Because of this, species that gestate embryos inside of their bodies need to have a genetic marker for sex to ensure that multiple sexes are represented among any given generation of children.
Asexual Reproduction in Reptiles
While most animal species reproduce sexually, the mourning gecko can sometimes produce and fertilize its own eggs. The offspring produced this way are genetically identical to their parent, making them essentially clones.
This has the advantage of making this species able to reproduce incredibly quickly, since each mourning gecko is guaranteed to produce at least two more identical offspring, and those two clones are fairly likely to survive since they are exactly the same as their mother.
However, the lack of genetic diversity in mourning geckos makes it extremely likely that they will eventually encounter a disease to which they are incredibly vulnerable, which will lead to their incredibly swift downfall.
This is exactly what happened to the man-made monoculture (species in which there is no genetic variance), the Gros Michael Banana in the early sixties. Even though the Gros Michael was present all over the world on banana farms, they went extinct extremely quickly as the result of a banana disease that they were vulnerable to.
So, now you know whether reptiles lay eggs or not! Reptile eggs are much more interesting than you might expect them to be, especially when you consider that most people do not consider them to be especially interesting. However, reptiles are just so cool that sometimes even learning very basic facts about them can still be a lot of fun. Just make sure to respect cool reptiles (and their eggs) from a distance!
The way that reptiles have babies is fascinating because it seems like each reptile has its own way of giving birth. If you have a reptile and are wondering how it has babies for various reasons, contact an expert, do research on the internet, or ask a veterinarian.