How do fleas live on pets and around homes?

1. Mango the cat keeps scratching. Something very small is living in the fur. Let's look closer, and then follow where its family lives.
2. Here is a flea, magnified. Its body is flat from side to side, so it slips between the hairs. It has no wings. Instead, it has huge back legs for jumping.
3. A mother flea lays dozens of eggs a day. The eggs are smooth and not sticky, so they roll out of the fur. They land wherever the pet rests: its bed, the rug, the sofa.
4. In a few days each egg hatches into a larva, like a tiny worm. Larvae avoid light, so they wriggle deep into the carpet, where they eat crumbs and specks.
5. After a week or two the larva spins a silk cocoon. Dust sticks to it, so it is hard to see. Inside, a new adult waits until it feels warmth and footsteps. Then it pops out and jumps.
6. Out of every hundred fleas, only about five are adults on the pet. The rest are eggs, larvae and cocoons in the home. So families wash pet bedding, vacuum, and ask a vet for the right flea treatment.

Tap each part of the flea. Find the spring that powers its jump.

• Flat body. A flea's body is squeezed flat from side to side, like a coin on its edge. That shape lets it slide quickly between the hairs of a pet.
• Tough shell. A flea wears a hard, smooth shell made of overlapping plates. It is very hard to squash, even when the pet scratches.
• Jumping legs. The back legs are long and strong. A flea can jump about 20 centimeters, which is around a hundred times its own body length.
• Spring pad. At the top of each back leg is a pad of rubbery stuff called resilin. The flea squeezes it slowly, locks it, then lets go. The pad snaps back and flings the flea into the air.
• Combs. Rows of stiff spines, called combs, point backward. If the pet tries to scratch the flea out, the combs catch on the hairs and hold it in.
• Mouth. An adult flea's mouth is like a very thin straw. It takes tiny sips of blood from the pet. The sips can make the skin itch.
• Senses. A flea has small eyes and short feelers. It senses warmth, movement and the breath of an animal, so it knows when a pet is near.

Choose where the cat naps, then let a week go by. Watch the eggs, larvae and cocoons in the three zoom windows. Where do most fleas live?

Experiment: After a few weeks, where are most of the fleas?

1. Let the cat nap on its bed and let a week go by. Look in the bed's zoom window.
2. Keep going for three more weeks. Watch eggs turn into larvae, then cocoons.
3. Move the cat to the rug and see where the new eggs land.

What we found: Most fleas are hidden in the home, not on the cat. The eggs fall where the cat rests, and the larvae and cocoons grow there. Cocoons wait until the cat comes back, then new fleas hop on.

Turn on JavaScript to try it yourself.

Make the home and the cat flea-free. Each week you can do two jobs, then let the week go by. For 3 stars, finish in two weeks.

Fleas are tiny insects without wings. A grown-up flea is about as big as a grain of sand. It lives in the fur of an animal such as a cat or a dog and takes tiny sips of its blood. Its body is flat from side to side, so it can slip between hairs, and its back legs are built for jumping.

A mother flea lays dozens of smooth, white eggs every day. Because they are not sticky, they roll off the pet. They land where the pet spends its time: in its bed, on the rug, on the sofa. In a few days they hatch into larvae, which look like tiny worms.

Larvae do not like light. They wriggle deep into carpets and bedding and eat specks and crumbs. After a week or two each one spins a cocoon. Inside, it changes into an adult. Then it waits, sometimes for weeks, until it feels the warmth and footsteps of an animal. Out it pops, and it jumps on.

This means that most fleas are not on the pet at all. Out of every hundred, about ninety-five are eggs, larvae and cocoons in the home. So families do two things together: a vet chooses a flea treatment for the pet, and the grown-ups wash pet bedding in hot water and vacuum often. Fleas are common, and having them does not mean a home is dirty.

Key words

Parasite

A living thing that lives on another animal and feeds from it.

Host

The animal a parasite lives on. For a cat flea, that is usually a cat or a dog.

Larva

The young, worm-like stage that hatches from the egg.

Pupa

The resting stage inside a cocoon, where a larva changes into an adult.

Resilin

A stretchy, springy protein that stores the energy for a flea's jump.

Check your thinking

1. What happens to flea eggs after they are laid?

   Show the answer

   They roll off the pet and land where it rests. Flea eggs are not sticky. They fall off the pet in the places where it spends its time.

2. A family finds fleas on their dog. Who should choose the flea treatment?

   Show the answer

   A vet, with a grown-up. A vet knows which treatment is safe for that animal's kind, size and age.

3. Out of every hundred fleas in a home, about how many are adults on the pet?

   Show the answer

   About 5. Only about five in a hundred are adults on the pet. The rest are hidden in the home.

4. Why can a flea cocoon wait so long before it opens?

   Show the answer

   It waits until it feels the warmth and footsteps of an animal. A new flea needs an animal to live on, so it stays safe in the cocoon until one comes near.

5. Which plan works best against fleas?

   Show the answer

   A vet's treatment for the pet, plus washing bedding and vacuuming. Fleas live in two places, on the pet and in the home, so both need care.