Animals reproduce in different ways. Some, like humans, give birth to live young. A few reproduce by budding – a new creature grows from a segment of the original animal. And many different types of animals have young that hatch from eggs.
Even among egg-layers, there are some differences and varieties. Some animals mate before laying eggs, while in other species such as fish, males and females release gametes at the same time, and the eggs are fertilized in a medium such as water. Some eggs are hard, while others are soft and squishy. Eggs may be kept in a nest on the ground, a nest in a tree, or even inside the body of one of the parents!
We’ve compiled a list of animals that lay eggs and some amazing facts about each one.
The Most-Consistent Egg Layers: Birds
Birds are unique in that all known species lay eggs. Different birds have wildly different methods for keeping eggs safe. Some sea birds roost in colonies, with millions of parents caring for eggs that are laid on the ground. Weaverbirds craft grasses into elaborate hanging structures to support their eggs. Male hornbills use mud to seal the mother bird and her eggs into a hole in a tree, leaving only enough space through which to pass food! This keeps many predators from reaching the nest.
#12 Animals That Lay Eggs: What Bird Lays the Smallest Egg?
The world’s smallest bird egg is laid by the world’s smallest bird – the bee hummingbird. The egg is 0.275 inches long and weighs only 0.0009 ounces.
Did you know? Some hummingbirds use sticky spider webs to hold together their tiny nests!
#11 Animals That Lay Eggs: What Bird Lays the Largest Egg?
It should come as no surprise that the largest bird egg is laid by the largest bird – the ostrich. The heaviest ostrich egg on record was laid by a captive individual. The egg weighed 5 lb 11.36 ounces. Typical ostrich eggs are 6 inches in length and weigh 3 pounds. That’s about the size of 20 chicken eggs!
Reptiles That Lay Eggs: Long Journeys and Live Births
Reptiles are diverse in their egg-laying styles. Some lay eggs, while others give birth to live young. A few are ovoviviparous, meaning the young grow inside an egg which remains inside the mother’s body until it is ready to hatch. One thing all egg-laying reptiles have in common is that they lay their eggs on land, even if the adults spend their lives in the water.
Consider the following list of some of the most interesting egg-laying reptiles.
#10 Animals That Lay Eggs: The Sea Turtle’s Egg-Laying Journey
Sea turtles always return to the beach where they were born in order to lay their eggs. For example, on a specific Costa Rican beach each October, tens of thousands of sea turtles crowd the beach in an event known as the arribada or “arrival.” They dig holes in the sand and lay their leathery eggs. Their young then hatch at the same time, and thousands of babies run the gauntlet of predators to get back to the ocean.
#9 Animals That Lay Eggs: Crocodiles: Nest Temperature Determines the Sex of Offspring
Like all reptiles, these aquatic creatures lay their eggs on the ground. They make nests on the riverbank, and the mother stays nearby to protect the nest and newly hatched offspring. One of the most interesting things about crocodiles, though, is that the location of the nest determines the sex or gender of the babies. How?
When the nest temperature is above 34 degrees centigrade (93.2 Fahrenheit), androgenic hormones form inside the egg. This results in male offspring. Lower temperatures do not produce these hormones, and the embryos remain female. So, a nest on a sunny riverbank will likely produce male crocodiles, while a shady nest produces females.
#8 Animals That Lay Eggs: Ovoviviparity: When Eggs Hatch BEFORE Being Laid
Some snakes, such as the garter snake, are ovoviviparous – young form inside an egg and are fed by the egg yolk, but the egg is retained inside the mother’s body rather than being laid in a nest. The baby snakes hatch inside the mother’s body and remain there for a time as they continue to grow. Unlike mammals, they do not receive food or oxygen from their mothers at this time. When mature, they are born alive. This gives them an advantage, as they are larger and more able to fend for themselves than they were at the time of hatching.
#7 Animals That Lay Eggs: Laying Eggs with No Shells: Amphibians
Frogs, toads, and other amphibians lay their eggs in water. The eggs do not have a hard shell. Instead, they are laid in a mass with the texture of jello. Some tropical frogs lay their eggs in tiny pools of water captured in tree branches or between plant leaves. The poison dart frog carries its newly hatched tadpoles, piggy-back style, from the trees to water sources on the ground.
Just the Right Nest: Insects and Arthropods
Many insects and arthropods lay eggs. Maybe you’ve seen the leaves of a tree covered in tiny round or pointed growths. Those are insect eggs! Most seek out a specific plant that will serve as food for the young. Some wasps take this to the next level, laying their eggs inside a living caterpillar. Once the eggs hatch, they devour the unlucky bug from the inside out.
#6 Animals That Lay Eggs: Cabbage Aphids: Born Pregnant
Most species require a male and a female to produce offspring. The cabbage aphid female, however, is able to produce genetic copies of itself, up to 10 offspring per day. In fact, the first embryo of the next generation can be seen inside newly hatched females with the aid of a microscope. Like the reptiles discussed above, the eggs hatch inside the mother’s body.
Late in the season, males are also born, as mating allows for genetic diversity. The females then lay eggs that will overwinter and hatch the next spring.
#5 Animals That Lay Eggs: Spiders That Take Their Eggs With Them
Most spiders place their eggs in a sack made of spider silk. These may be hidden underground or supported by a web. But a few spider species take their eggs with them. Nursery web spiders use their mouthparts to carry the egg sac. Wolf spiders attach the egg sac to their spinnerets, at the back of the abdomen. When the eggs hatch, the baby spiders climb onto the mother’s back and spend their first days there. If you try to squish the mother wolf spider, the baby spiders will scatter!
Unique Egg Strategies: Fish
Like reptiles, fish have several different reproductive strategies. They may retain eggs in the body and give birth to live young. Or, rather than mating with one individual, they may release their eggs in mass spawning events so that water-borne gametes from many different males may fertilize the eggs.
Here, we list some of the most interesting fish egg stories.
#4 Animals That Lay Eggs: Seahorses: How Males Give Birth
Seahorses are often lauded as the only species in which males, rather than females, give birth. This is because the eggs are stored in a special pouch on the male’s stomach. After they hatch, he gives birth to live young.
#3 Animals That Lay Eggs: Sturgeons: Hunted for Their Eggs
Have you ever tasted caviar? This food, considered a delicacy, is actually fish eggs. A large fish called the sturgeon was nearly hunted to extinction because its eggs were highly sought after. Today, the sturgeon are protected by the Endangered Species Act, and new methods allow eggs to be collected without harming the fish.
#2 Animals That Lay Eggs: Mammals That Lay Eggs: The Monotremes
There are a few things we know about mammals: they are warm-blooded, have hair, feed their young with milk, and give birth to live young. But there are five mammals that take exception to the last rule – the platypus and four echidna species.
These species, classified as monotremes, are mammals that lay eggs. The mother carries the eggs inside her body for a time, providing the nutrients. She lays the eggs in a nest or den, and they hatch about 10 days later. The babies, called “puggles,” are underdeveloped when they hatch, much like newborn marsupials. Unlike other egg-layers, monotremes feed their young with milk just like all other mammals. Uniquely, though, the monotremes excrete milk through glands in their skin rather than through a nipple or teat.
#1 Animals That Lay Eggs: Laying the Most Eggs: Corals
You may not think of coral reefs as producing eggs. But during a spawn, a single coral can produce and release millions of eggs during a 2-day period each year. This is considered a “risky” reproductive strategy, however, as many filter-feeders come to feast on the eggs and larvae. Out of the millions of potential offspring each coral releases, approximately two will survive to adulthood.