How to get rid of fleas in the house

The adults you see are a small fraction

This is the single most useful thing to understand about fleas. The jumping adults are a minority of the population; the bulk is eggs, larvae and pupae sitting in carpet pile, under furniture, in bedding and down the gaps between floorboards.

That's why treating the pet alone never works, and why a treatment that looks successful on day one goes wrong on day ten.

Vacuuming does more than you'd think

Vacuuming physically removes eggs and larvae, and the vibration triggers dormant pupae to hatch - which sounds bad but is exactly what you want, because it brings them out where treatment can reach them.

Do it thoroughly: carpet edges, under furniture, along skirting, pet resting spots. Empty the vacuum outside afterwards.

Treat the pet and the house at the same time

Doing one without the other guarantees a repeat. An untreated pet reseeds the house within days; a treated pet in an untreated house picks up fleas again from the carpet. Your vet is the right person for the animal side.

Why they're still appearing three weeks later

Flea pupae are sealed in a cocoon and are highly resistant - they can sit dormant for months and hatch when they detect warmth, carbon dioxide and movement. Nothing kills them reliably in that stage.

So fleas appearing after treatment isn't a failed treatment. It's the pupae hatching into it, which is how it's meant to work. Keep vacuuming through this period.

No pet, but fleas anyway?

Common, and the answer is usually rodents or possums in the roof or subfloor, or a previous occupant's pet. Fleas came in on the animal, the animal left or was dealt with, and the fleas are looking for the next host. If that's the situation, treating the fleas without dealing with the rodents just buys you time.