Why the Fleas Came Back (The Pupal Window)

You did everything right. You took the dog to the vet. You washed all the bedding. You paid an exterminator to spray the carpets.

The fleas were gone for two weeks.

Then, suddenly, they are back. You are getting bitten on the ankles again. You think the exterminator ripped you off.

He didn't. You are experiencing The Pupal Window.

The Bulletproof Cocoon

To understand flea control, you have to understand biology. Fleas have four stages: Egg, Larva, Pupa (Cocoon), Adult.

Modern insecticides kill adults and larvae easily. They also stop eggs from hatching.

But nothing kills the Pupa.

The cocoon is a watertight, chemical-proof armor. The sprays you use just sit on top of the cocoon. The flea inside is safe. It develops into an adult and waits.

The Vibration Trigger

This is the creepy part. The adult flea inside the cocoon can stay dormant for months. It waits for a signal that a host is nearby.

That signal is vibration (footsteps) and carbon dioxide (breath).

When you walk by, they hatch instantly and jump. That is why you see a "second wave" 2-3 weeks after treatment. It's the new adults waking up.

You Must Vacuum to Kill Them

This sounds counter-intuitive, but you want them to hatch.

After you spray, you must vacuum every single day. The vibration of the vacuum cleaner tricks the fleas into thinking a giant dog is running by. They hatch into the carpet.

Since the carpet is already treated with poison, they hatch and die immediately. If you don't vacuum, they stay in the cocoon until the poison wears off, and then you start all over again.