Name Two Animals That Lay Eggs

Two Animals That Lay Eggs (And Why It's Not Always Obvious)

Most people can name a chicken. Also, maybe a duck, if they're thinking about it. But the list of egg-laying animals is wildly longer than anyone learns in school, and some of the entries are honestly surprising.

Here's a quick answer up front, then we'll dig into why this question is more interesting than it sounds: chickens and platypuses. Yes, really — a platypus. Keep reading.

What "Egg-Laying Animals" Actually Means

In biology, egg-laying animals are called oviparous*. That's the formal term for creatures that reproduce by laying eggs, with the embryo developing mostly outside the mother's body. It's one of three main reproductive strategies in the animal kingdom, alongside viviparous* (live birth, like most mammals) and ovoviviparous* (eggs hatch inside the mother, then babies are born live — sharks do this sometimes).

So when someone asks you to name two animals that lay eggs, they're really asking you to name two oviparous* species. The pool is enormous. Birds, most fish, almost all reptiles, amphibians, insects, arachnids, and a handful of very weird mammals all qualify.

But here's the fun part: not all of them lay the kind of egg you'd picture.

Chickens — The Obvious One

Chickens are the world's most common egg-laying animal by sheer volume, and the one everyone thinks of first. A single commercial laying hen can produce well over 300 eggs a year, depending on the breed and conditions. Domestic chickens descended from the red junglefowl of Southeast Asia, and humans have been keeping them for thousands of years — partly for eggs, partly for meat, and historically for cockfighting too.

Their eggs are amniotic*, which is a feature birds share with reptiles. That's why the shell is mostly calcium carbonate, the inside has a yolk for nutrition, and there's an air cell at the wide end that the chick breathes from before hatching. Incubation takes around 21 days.

Nothing shocking here. So chickens are the safe answer. But let's get to the weird one.

Platypuses — The One That Breaks the Rule

The platypus is a mammal. It's warm-blooded, has fur, feeds its young milk. And yet it lays eggs.

It's one of only five existing species of monotremes* — egg-laying mammals — and along with the four echidna species, it represents the earliest branch of the mammalian family tree. Which means when you see a platypus on a nature show and the narrator casually mentions it lays eggs, you can almost feel the documentary producers smirking. They know the audience does a double-take every time.

A female platypus typically lays one to three small, leathery eggs — more reptilian than bird-like — in a burrow. The whole setup is so unusual that when European naturalists first saw a platypus specimen in the late 1700s, some thought it was a hoax. In practice, a stitched-together animal. She curls around them for about ten days until they hatch, then feeds the babies milk that seeps out of patches on her skin (platypuses don't have nipples, which is itself a whole thing). Real talk, you can understand why.

Why It Matters That Some Mammals Lay Eggs

This is the part most short answers skip past, and it's where the question gets genuinely interesting.

Monotremes like the platypus are living evidence of an evolutionary transition. Mammals as a group are thought to have evolved from earlier egg-laying ancestors — and monotremes kept that ancestral trait while also developing the mammalian features we associate with the group (fur, milk, warm-bloodedness). In a sense, they show us a "middle" stage that otherwise only exists in the fossil record.

If you only ever thought of mammals as live-birthers, the platypus quietly proves that's a generalization, not a rule. The same goes for echidnas, which are also monotremes and also lay eggs.

So when a trivia question asks for two egg-laying animals, picking a chicken and a platypus is a much better answer than picking two birds. It shows you understand the underlying biology, not just the surface-level association between "eggs" and "chickens."

More Animals That Lay Eggs (Because the List Is Long)

The chicken-and-platypus combo is a strong answer, but if you want more options, here are some others worth knowing:

• Sea turtles — they haul themselves onto beaches, dig nests, and lay dozens of soft-shelled eggs. Temperature during incubation determines the sex of the hatchlings, which is one of the wildest facts in all of biology.
• Frogs and toads — most lay eggs in water, though some tropical species have figured out clever alternatives (carrying eggs on their back, hiding them in foam nests, etc.).
• Salmon — they hatch in freshwater streams, migrate to the ocean, then return to spawn. Their egg-laying is part of one of the most dramatic life cycles in the animal kingdom.
• Crocodiles — yes, they lay eggs too, and the mothers guard the nest aggressively. The babies chirp when ready to hatch, which prompts the mother to help them out.
• Spiders — almost all species lay eggs, often wrapped in silk sacs. A single sac can contain hundreds of eggs.
• Emus — Australia's giant flightless bird, and a close relative of the ostrich. Both lay impressively large eggs.

Common Mistakes People Make About Egg-Laying Animals

Assuming all mammals give live birth

This is the big one. They aren't. Practically speaking, most introductory biology classes treat "mammal" and "live birth" as a package deal. The platypus and the echidna are the two exceptions that prove the rule, and the rule was never as firm as people think.

Confusing eggs with reproduction strategy

Eggs aren't just about birds and breakfast. Egg-laying shows up across wildly different branches of the tree of life, and the eggs themselves look nothing alike. A chicken egg, a frog egg, a spider egg sac, and a platypus egg are all "eggs" in the broad biological sense, but they differ in size, shell, and how the embryo is nourished.

Thinking only birds lay hard-shelled eggs

Hard shells are a bird-and-some-reptile thing. Fish eggs, frog eggs, and platypus eggs are all soft. Even among reptiles, snakes and most lizards lay leathery eggs, not hard ones.

Forgetting that some "live-bearing" animals technically use eggs internally

Sharks and some snakes are ovoviviparous* — the eggs form and hatch inside the mother, who then gives birth to live young. So even some "live birth" cases are still egg-based at the cellular level. The categories bleed into each other more than textbooks suggest.

Quick Tips for Answering This Kind of Question

If you ever get asked to "name two egg-laying animals" in a quiz, classroom, or trivia game, here's what I'd actually recommend:

If you found this helpful, you might also enjoy the individual sacs formed by the inner membrane are called or the shape of the water molecule h2o is.

• Pick one familiar and one unusual. A chicken plus a platypus is a much more memorable answer than two chickens.
• Know what makes your answer interesting. Just naming a duck won't get you points. Naming a platypus and briefly explaining monotremes will.
• Don't forget non-vertebrates. Fish, insects, spiders, and amphibians all lay eggs. If the question allows it, naming one of these can really stand out.
• Have a follow-up ready. Anyone can list two animals. Being able to add "and here's why that's biologically interesting" is what makes an answer stick.

FAQ

Are platypuses the only egg-laying mammals?

No, but they're the most famous. There are five living monotreme species total — the platypus and four species of echidna. All of them lay eggs.

Do all birds lay eggs?

Yes. Even so, every single bird species lays eggs. Now, there are no live-bearing birds. The same is true of all reptiles, all amphibians, and most fish.

How many eggs does a chicken lay in a lifetime?

It depends on the breed and how long it lives, but a healthy laying hen can produce somewhere in the range of several hundred eggs per year. Over a typical productive lifespan of a few years, that adds up to over a thousand.

Why did evolution keep egg-laying in some mammals?

That's still an open question, and researchers don't have a complete answer. Monotrem

Why did evolution keep egg‑laying in some mammals?

Monotremes—those oddball mammals that include the platypus and the four echidna species—still lay eggs because they sit at the very base of the mammalian family tree. The common ancestor of all living mammals almost certainly reproduced by laying eggs, a strategy that was later replaced in the lineages that gave rise to marsupials and placentals by live birth (either through the development of a placenta or extended gestation in a pouch). When monotremes split off, they retained the ancestral method, and the pressures that favor egg‑laying in their particular habitats never shifted enough to force a switch.

Several factors help explain why egg‑laying persisted in these lineages:

1. Energy trade‑offs – Producing a shelled egg is energetically cheaper than maintaining a uterus and a placenta, especially for animals that have a low metabolic rate and a diet that doesn’t provide a steady supply of high‑quality nutrients. Echidnas, for instance, are insectivores that can store fat reserves; a relatively modest egg allows them to invest only a short period of incubation rather than months of internal development.

2. Thermoregulation flexibility – Unlike placental mammals, monotremes lack a highly controlled internal furnace to keep a developing fetus warm. By laying eggs, they can place them in a thermally stable environment—such as a burrow or a shallow nest—where ambient temperature can be regulated behaviorally (e.g., by the mother curling around the clutch). This is especially valuable for the platypus, which lives in temperate streams and can keep its eggs warm by using the surrounding water’s moderate temperature.

3. Ecological niche stability – The habitats occupied by extant monotremes—freshwater streams, temperate forests, and arid shrublands—have remained relatively unchanged since the early Cenozoic. In such stable environments, the egg‑laying strategy, with its modest energetic demands and relatively simple parental care, proved “good enough” and was not outcompeted by more energetically expensive viviparous alternatives.

4. Evolutionary constraint – Genetic and developmental pathways that govern egg formation (e.g., vitellogenesis, shell deposition, and incubation behaviors) are deeply ingrained in monotreme genomes. Switching to live birth would require major rewiring of these pathways, which is unlikely to happen without strong selective pressure. Because monotremes have survived without such pressure, the ancestral mode endures.

5. Reproductive timing – The timing of egg laying in monotremes is tightly linked to seasonal resource abundance. Platypus females breed once a year after the wet season when food is plentiful, ensuring that hatchlings have ample nourishment. In contrast, viviparous mammals often need to time gestation to match resource peaks, a more complex synchronization that monotremes avoid by external incubation.

Taken together, these factors illustrate that egg‑laying in monotremes is not a “primitive flaw” but a finely tuned adaptation to their particular ecological and physiological circumstances. The persistence of this strategy underscores a broader principle in evolutionary biology: reproductive modes are not binary “good” or “bad” choices, but solutions that are shaped by the interplay of anatomy, environment, and historical contingency.

Conclusion

Eggs are far more than a breakfast staple or a textbook illustration of avian reproduction. They appear in a staggering array of forms—from the microscopic, yolk‑laden spheres of fish to the leathery clutches of snakes, from the silk‑wrapped sacs of spiders to the hard‑shelled gems of chickens. The diversity of egg‑laying strategies reveals how life solves the fundamental problem of embryonic development across vastly different environments and phylogenetic lineages.

Understanding this diversity helps demystify common misconceptions—such as the belief that only birds produce hard‑shelled eggs or that live birth and egg‑laying are mutually exclusive. In reality, the boundaries between oviparity, ovoviviparity, and viviparity are porous, and many species employ a blend of these strategies depending

on environmental conditions, life‑history stage, or even individual circumstance.

For monotremes, the retention of oviparity illustrates how a “primitive” trait can persist when it remains functionally adequate. Their eggs are not vestiges of an outdated past but are integrated into a suite of adaptations—physiological, ecological, and behavioral—that together enhance fitness. The platypus’s webbed feet, electroreceptive bill, and the echidna’s spines all coexist with an egg‑laying reproductive mode, demonstrating that evolution does not discard a trait simply because it is ancient; it preserves what works.

In a broader sense, the study of eggs invites us to appreciate the creativity of life. Each egg is a self‑contained universe, a temporary shelter that supplies nutrients, protection, and a controlled microenvironment for a developing embryo. Whether encased in calcium carbonate, parchment‑like membrane, or gelatinous coating, the egg is a masterpiece of natural engineering.

As we continue to explore the natural world, the humble egg will undoubtedly reveal more secrets. New discoveries of fossilized embryos, molecular insights into yolk protein evolution, and comparative studies of reproductive genomics promise to deepen our understanding of how and why oviparity has persisted, transformed, or been abandoned across the tree of life. In recognizing the egg’s centrality, we gain not only knowledge of biology but also a renewed sense of wonder for the myriad ways life perpetuates itself.