Egg-Laying Animals

Let’s start with a quick question: What do we call animals that reproduce through eggs? And another: What do we call animals that lay eggs? You may think the answers are identical, but actually they are not. In this article, we will explain the difference and provide a detailed list of egg-laying animals, their characteristics, and some fascinating examples.

What Do We Call Egg-Laying Animals?

When it comes to reproduction through eggs, there are oviparous animals and ovoviviparous animals.

• Oviparous animals are those that lay eggs in the external environment. The embryos develop inside these eggs until they hatch.

• Ovoviviparous animals, on the other hand, also reproduce through eggs, but the eggs remain inside the body of the female (and in rare cases, the male, such as seahorses) until hatching occurs. As a result, the offspring are born alive, despite originating from eggs.

In short:

• Oviparous = eggs are laid outside the body.

• Ovoviviparous = eggs remain inside until hatching, producing live young.

• Viviparous = embryos develop fully inside the womb, nourished by the placenta, and are born alive.

Characteristics of Oviparous Animals

Oviparous animals develop their embryos inside eggs laid in the external environment. The protective shell or membrane provides moisture control and safety against environmental threats.

Different groups of oviparous animals have different egg-laying strategies:

• Birds: build nests in trees or on the ground.

• Reptiles: many species, such as turtles, bury their eggs in sand or soil.

• Fish & Amphibians: usually lay eggs in water, surrounded by a gelatinous coat.

• Insects & Mollusks: lay numerous eggs, often with little parental care.

• Mammals (Monotremes): the platypus and echidna are the only mammals that lay eggs.

Internal vs. External Fertilization

• Internal fertilization: eggs are fertilized inside the female’s body before being laid (birds, reptiles). These eggs often have hard or leathery shells.

• External fertilization: eggs are laid first, and then fertilized outside by the male (many fish and amphibians). These eggs are usually soft.

Examples of Oviparous Animals

Here are some of the most representative egg-laying animals:

• Reptiles: crocodiles, vipers, iguanas, turtles, Komodo dragons, lizards

• Amphibians: frogs, toads

• Fish: salmon, trout, carp, tuna, cod, pufferfish, clownfish

• Insects & Arachnids: ants, bees, butterflies, wasps, ladybugs, beetles, flies, mosquitoes, cicadas, cockroaches, crickets, scorpions, silkworms

• Mollusks: squid, snails, octopuses, slugs

• Birds: penguins, sparrows, chickens, hawks, parrots, peacocks, ostriches, storks, ducks, owls, crows, pigeons

• Mammals (monotremes): platypus and echidna

Ovoviviparous Animals

Ovoviviparous animals are the “middle ground” between oviparous and viviparous species. The eggs remain inside the female (or male in the case of seahorses) until the embryo is ready, and then the offspring are born alive.

Examples include:

• Sharks: bull shark, dogfish, great white, whale shark, tiger shark

• Rays: manta rays

• Reptiles: boa constrictors, anacondas, some vipers, iguanas, and chameleons

• Fish: guppies, mosquitofish

• Amphibians: Surinam toad, certain tropical frogs

• Special case: male seahorses carry the eggs until hatching

Summary

• Oviparous animals: lay eggs in the external environment, where embryos develop and hatch.

• Ovoviviparous animals: embryos develop in eggs inside the parent’s body and hatch internally, producing live offspring.

• Viviparous animals: embryos develop directly inside the womb, nourished by the placenta, and are born alive.

Both egg-laying and egg-retaining strategies represent evolutionary adaptations that increase survival in different habitats.

animal tags： egg laying animals