How does a platypus find food with its eyes shut?

A very unusual hunter

The platypus lives only in Australia, in the rivers, creeks and lakes of eastern Queensland, New South Wales, Victoria and Tasmania. With its duck-like bill, flat tail and webbed feet, it looked so strange that when the first specimen reached England, many scientists thought it was a fake.

The platypus is a monotreme. Along with echidnas, it is one of the only mammals that lay eggs. It also has a very unusual way of finding dinner. It hunts mostly at night, often in muddy water, searching the riverbed for small animals such as insect larvae, freshwater shrimps, worms and snails.

And here is the strangest part: every time it dives to hunt, it shuts its eyes, its ears and its nostrils.

Diving with its senses switched off

When a platypus slips under the water, its eyes close automatically. Its ears sit in a muscular groove that pinches shut, and its nostrils close too. Imagine hunting for food in a dark, murky creek while wearing a blindfold, earmuffs and a nose peg!

It paddles with its webbed front feet and steers with its back feet, using its bill to search through the gravel and mud. That bill is nothing like a duck's hard beak. It is soft, bendy and covered in smooth skin that feels a bit like suede.

The soft bill is the platypus's secret weapon, because it is packed with tens of thousands of tiny sensors.

A bill that can feel electricity

Some of the sensors are for touch. They are called push rods, and they are so sensitive that a platypus can feel the water move when a freshwater shrimp flicks its tail at least 15 to 20 centimetres away.

The other sensors are even more surprising. The bill has about 40,000 electroreceptors, which can sense electricity. Whenever an animal moves, its muscles give off a tiny electrical signal. A wriggling insect larva or a darting shrimp is sending out a faint electric message without knowing it, and the platypus can pick it up.

Scientists showed this in 1986, when experiments proved that a platypus could find and avoid objects using weak electric fields in the water. This sense, called electroreception, was already known in some fish, including sharks, but it had never been found in a mammal before. Echidnas turned out to have it too, though with far fewer sensors.

The lightning-and-thunder trick

Knowing that food is nearby is one thing. Knowing exactly where it is takes a clever trick.

When a shrimp flicks its tail, it makes two signals at once: a tiny burst of electricity and a little push of moving water. Electricity travels through water almost instantly, but the water movement travels much more slowly. So the electric signal reaches the bill a split second before the ripple does.

Scientists think the platypus uses that tiny gap to judge distance, just as you can tell how far away a storm is by counting the seconds between the lightning flash and the thunder. The bigger the gap, the farther away the prey. Its brain puts together the signals from thousands of sensors across the bill to work out exactly where the prey is.

Dive, collect, chew, repeat

Once it finds something to eat, the platypus snaps it up and tucks it into its cheek pouches, near the back of its bill. Most dives last less than a minute. Then it floats back to the surface, breathes, and spends 10 to 20 seconds chewing its catch before diving again.

Adult platypuses have no teeth. Young ones have a few, but these fall out and are replaced by rough grinding pads that keep growing as they wear down.

A platypus needs a lot of food to stay warm and healthy. Studies suggest it eats roughly a fifth of its own body weight every day, and it can make up to 1,600 dives in a single feeding session.

Platypuses need clean creeks to hunt in, so keeping rivers free of litter, especially old fishing line, helps them. Next time you are near a creek at dusk and spot a small, quiet ripple, look closely. It could be a platypus, hunting with its eyes shut.

📚 Words to know

Electroreceptor

A sensor that can detect tiny amounts of electricity.

Monotreme

A mammal that lays eggs. The platypus and the echidnas are the only monotremes alive today.

Push rod

A tiny touch sensor in the platypus bill that feels movements in the water.

Invertebrate

An animal without a backbone, such as an insect, worm, snail or shrimp.

Cheek pouch

A pocket inside the cheek where an animal can store food for a while.

🧪 Try this: hunt like a platypus

1. Fill a shallow tray with dry rice or sand. Ask a friend to hide ten small objects in it, such as pasta shapes, buttons and bottle caps.
2. Close your eyes (or wear a blindfold) and find all ten objects using only your fingertips. Time yourself, then swap roles.
3. Now try a ripple test. Half fill a large tub with water and rest your hand gently on the surface with your eyes closed. Your friend makes small ripples with one finger at different sides of the tub. Can you point to where each ripple came from?
4. Think about it: your fingertips are full of touch sensors, but they have no electroreceptors. A platypus bill has both, so it can tell what is moving and exactly where it is.