What Can Kill Fleas Instantly?

When battling fleas (in all their 4 life stages), pet owners will turn to any effective and safe method. But, you ask, what can kill fleas instantly?

  • In summary, Boron-based products such as Boric acid (a desiccant) will kill fleas instantaneously. When mixed with botanical pesticides, boric acid will kill the egg and larvae stages by dehydrating them.
  • Flea pupae and adult fleas are killed by pyrethrin-based IGRs (insect growth regulators – IGRs) used with vacuuming, heat treatment or washing the pet bedding.

In this article we examine what can kill fleas instantly with 3 different solutions.

Our first solution is using a boron based desiccant (boric acid), the second is using IGR-based pyrethrin product and thirdly we will utilize vacuuming. To learn more, read on!

What Is Boric Acid?

Boric acid is a naturally occurring substance found in the earth derived from boron. Borax, a boric acid salt compound, is used as an insecticide for insects such as fleas, ants, termites, and cockroaches.

  • Boric acid usually comes in the form of long, crystalline looking grains. The crystals or powder dissolve easily in water.

Boric acid is a colorless and odorless substance that leaves no residue on surfaces.

What Can Kill Fleas Instantly? – Use Boric Acid

It depends how the person means ‘instantly’. If they mean that boric acid will kill fleas within 24 hours of mixing it with a botanical insecticide then this is true.

But if they mean that boric acid can kill all fleas – including eggs, larvae and pupae – then this is not true.

Boric acid does have some control over flea eggs, larvae and pupae but it will only kill the newly laid eggs and larvae but it cannot get to those which are already adults or in their cocoon phase because they’re protected by a hard shell called a pupal case.

If combined with botanical insecticides, boric acid will damage the insects’ exoskeletons and work like a stomach poison when ingested by fleas leading to their death.

1. Borax to kill Flea Eggs

Flea eggs are soft (white), and thus boric acid will soaking and dehydrate them causing their death.

Boric acid mixed with botanical insecticides like pyrethrin will easily kill those flea eggs in your yard, house, flooring, bedding, and carpets.

Boric acid kills flea eggs by destroying the exoskeleton of insects and disrupting their central nervous systems.

Lastly, boric acid should be used for your infested area because it can be applied to the ground, carpets, and cracks in the flooring without harming human skin.

2. Borax to kill Flea Larvae

Borax, Boric acid, is a powdery white pesticide that kills flea larvae by dehydrating them.

Boric acid should be mixed with carriers like shredded soap and and sprinkled around the house to kill those flea larvae in cracks, flooring, bedding, and carpets.

You can also use borax to kill flea larvae by spraying it on the yard and then watering it.

Using Borax for Flea Treatment

This borax method has been shown to be effective in killing fleas ‘instantly’. To kill fleas eggs and larvae, follow these steps:

  1. Vacuum your carpets, furniture, and other surfaces.
  2. Sprinkle the borax powder in infested areas to kill fleas on contact. Apply borax treatment to the carpet at a typical application rate of 4 ounces per 100 square feet.
  3. Following safety precautions from Web MD, such as vacuuming and discarding your vacuum cleaner bag.
  4. Use a broom or broad brush to scrub or brush the Borax powder into the objects like the carpet
  5. After the borax is shaken on your carpet, allow it to sit for 6-48 hours or longer.
  6. During the freeze time, make sure any pets or kids are not close to the area.
  7. Vacuum the molding and cracks among other hard-to-reach places to remove fleas using a vacuum hose
  8. The vacuum bags will contain flea larvae, so make sure to discard them in a place outside of the house to avoid re-infestation

Treating your pets at the same time you’re treating the surfaces is crucial, so be sure to use flea shampoo or other products for them as well.

  • Caution: Borax should not be used simultaneously on your pets, since it can develop into a fatal result.

Boric Acid vs. Borax

Borax is not as effective on fleas compared to boric acid. Boric Acid is a more concentrated substance than Borax and kills the larvae faster.

Both Borax and Boric Acid can be found in products such as cosmetics, soaps, and insecticides.

Sodium borate, known commonly as borax, is an alkaline compound of the element Boron and classified as a salt with the appearance of crushing-white powder.

  • The compounds Borax (Na2B4O7) and Boric Acid (H3BO3) are collectively confused due to their similarity in chemical structure.

If you’re using Boric Acid for a surface, then make sure to use gloves while applying, and stay away from any areas where children or pets may come into contact with it.

  • If ants have invaded your home in the past few days, you’ll need to kill them quickly before they spread out any further.
  • Boric acid can be used for this purpose; just sprinkle it on top of the ant hill and they’ll be gone within a few hours.

In order for the borax treatment to be effective, your pets should stay away from that area until they’re completely dry.

Ideally, this will take about 48 hours; but if there’s a lot of precipitation in the air (rain or snow), it could take up to 72 hours for the Boric Acid treatment to work.

Boric acid is one of the cheapest and most effective solutions you’ll find, but if they’re still a problem after that, you can always call an exterminator in your area or buy some over-the-counter treatments at a local pet store.

3. Pyrethrin IGRs to kill Flea Pupae

Pyrethrin will be effective in killing flea pupae – the eggs that have yet to hatch. Wet the area and vacuuming to make the flea larvae to hatch, allows the Pyrethrin IGRs to kill them.

The problem is that it will take anywhere from a week to two weeks for the pyrethrin IGRs to fully kill all of the pupae in your house, which means you’ll still be dealing with an infestation while this process takes place.

Some suitable Pyrethrin IGRs include;

  • Precor 2000 Plus
  • NyGuard IGR
  • Gentrol IGR

Invermectin alone will not kill fleas. It can only prevent them from hatching and it does nothing to the ones that are already in your home.

Pyrethrin IGRs work by preventing the development of larvae that have already been laid in your house, which means you’ll still need to deal with an infestation while this process takes place.

To kill flea pupae, you’ll require to irritate them to hatch from their cocoons through vacuuming the surfaces. Vacuum the surfaces of your carpet, flooring, furniture and bedding.

3. Vacuum, Sprays, Foggers to kill Adult Fleas

To kill Adult Fleas, these methods;

a. Vacuum

Begin by vacuuming thoroughly in all the areas that are infested with fleas.

This is important because it will catch adults and kill pupae as they hatch from cocoons (see points above for more info on how to kill pupae).

b. Flea Spray

At the same time, you can spray your carpets or any other surfaces that are infested with flea adult ticks with a pyrethrin IGR product.

They’re designed specifically to kill adult fleas (follow manufacturer’s instructions and do not use if children, pregnant women or animals are present).

c. Flea Fogger

Alternatively, you can use a flea fogger to kill the adult fleas and their eggs on your carpets.

Do this at least once every six months (or more often if required) in conjunction with vacuuming as detailed above.

Remember that these products will not kill eggs laid after the fogging.

d. Flea Traps

If you have a flea infestation in your carpet, it is wise to use flea traps.

These will capture and hold adult fleas as well as their larvae before they are able to climb up into carpets where they can live for many months.

Treat these traps with a suitable insecticide as directed.


On what can kill fleas instantly; use boric acid, pyrethrin IGRs, and vacuuming.

Flea foggers are a good option if you have a massive flea infestation.


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