# Do any mammals lay eggs?

> Yes. Monotremes — the platypus and four echidna species — lay leathery eggs and are the only egg-laying mammals. They still nurse young with milk. Monotremes are the only egg-laying mammals. The platypus and four echidna species split from other mammals roughly 180 million years ago.

**Category:** Wildlife  ·  **Updated:** 2026-07-05

## Key takeaways
- Platypus and echidnas are egg-laying mammals (monotremes).
- They still produce milk — mammals by definition.
- Five living species — Australia and New Guinea only.
- Platypus Vulnerable — drought, traps, habitat loss.
- Venom and electroreception in platypus — unique among mammals.
- Live birth is not required to be a mammal.

## Answer
Monotremes split from other mammals roughly 180 million years ago. The platypus is endemic to eastern Australia; echidnas live in Australia and New Guinea.

Platypuses are venomous — males have spurs on hind legs — and use electroreception to detect prey in murky water.

Habitat degradation, drought and entanglement in fishing gear threaten platypus populations; several assessments have moved toward Vulnerable or Endangered status regionally.

## Monotreme reproduction
Female platypuses lay one to three leathery eggs in a burrow after mating. Incubation lasts about ten days; hatchlings are blind and hairless, lapping milk from abdominal patches. Echidnas carry a single egg in a temporary pouch — puggle hatches and nurses until spines develop. This combines reptilian egg laying with mammalian lactation — defining mammals by milk production, not live birth alone. Gestation and incubation are short relative to placental mammals; parental investment continues through prolonged nursing.

## Platypus oddities
Platypuses detect prey electric fields through bill receptors — hunting with eyes, ears and nose closed underwater. Males possess ankle spurs delivering venom painful to humans though rarely fatal. Webbed feet and dense fur suit cold Australian streams. Genetic studies once baffled nineteenth-century scientists who suspected hoax specimens. Today genetics place monotremes on their own evolutionary branch — ten sex chromosomes in platypus versus two in humans.

## Echidnas
Short-beaked echidnas range across Australia and New Guinea in diverse habitats; long-beaked echidnas live in New Guinea forests and are Critically Endangered. Spines defend against predators; powerful claws dig for ants and termites. Echidnas enter torpor during cold or fire — surviving burns by sheltering in logs. Low reproductive rate — one puggle every few years — makes population recovery slow after local declines.

## Conservation
Platypus listed Vulnerable by IUCN in 2021 after regional declines from drought, river regulation, pollution and yabby trap drowning. Land clearing removes riparian vegetation. Climate change intensifies drought and fire. Monotremes illustrate that egg laying does not mean primitive or secure — all five species need habitat protection. Accurate public understanding counters assumption that mammals always bear live young.

## FAQ
### Which mammals lay eggs?
Monotremes only — platypus and four echidna species in Australia and New Guinea.

### Do egg-laying mammals produce milk?
Yes. Females nurse young — milk from skin patches in monotremes.

### Are platypuses venomous?
Males have venomous hind-leg spurs — painful to humans, used in male combat.

### Are platypuses endangered?
IUCN Vulnerable (2021) with declining populations in parts of eastern Australia.

### Why do monotremes lay eggs?
Evolutionary retention from ancestors predating placental and marsupial divergence — still fully mammalian.

### Can monotremes be pets?
No — protected native wildlife in Australia; illegal and harmful to take from wild.

## Sources
- [IUCN Red List — Ornithorhynchus anatinus](https://www.iucnredlist.org)

Human-readable page: https://worldanimalrescuenetwork.org/answers/do-any-mammals-lay-eggs