How is Boric Acid Able to Kill Insects When It is Only as Toxic as Table Salt?

Updated on August 30, 2009

Boric acid is often used as an insecticide and can be very effective at controlling cockroaches, as well as small ants. However, in humans, boric acid is only slightly more toxic than table salt.

So, how is boric acid able to kill cockroaches, when it is only slightly more toxic than table salt?

The short answer is that boric acid affects the body of an insect much differently than it does a human or other mammal.

This does not mean that boric acid is safe for humans or animals to consume though, but only that it takes less boric acid to kill insects.

When considering the comparison of boric acid to table salt, it is important to remember that many of the things we regularily eat are actually toxic if consumed in excess. For example, caffeine is almost 14 times more toxic to humans than boric acid.

More information about boric acid is below, including how to save money by making your own homemade ant traps.

What is Boric Acid?

Boric Acid is often used to kill insects and has many other industrial uses. It is a weak acid that often comes in an odorless colorless powder, which can be dissolved in water.

Boric acid was first discovered over 400 years ago by Wilhelm Homberg, who was able to extract boric acid from a type of salt called borax. Today, borax has many uses and is often used in laundry detergents.

Toxicity of Boric Acid

It is often stated that boric acid has the same toxicity as ordinary table salt in humans, which can be a little misleading. To understand what this means, it is important to understand a little bit about toxicology.

In the medical field an objects toxicity is usually described as an LD50 value. The LD50 is the Lethal Dose required to kill 50% of those who are exposed to it. Typically rats are used to calculate an LD50 value.

Boric Acid has a LD50 value of 2,660 mg/kg. This means that in about half of those who weigh 80kg(176 lbs,) 212gm(.49lbs) of boric acid would be a lethal dose.

Table Salt has a LD50 value of 3000 mg/kg. This means that in about half of those who weigh 80kg (176lbs,) 240 grams (.52lbs) of table salt would be a lethal dose.

Using Boric Acid as an Insecticide

Boric acid can be very effective at controlling cockroaches, sugar ants, and other household insects. If you goto most hardware stores, you will notice that many common insecticides list boric acid as the main ingredient.

Homeade Boric Acid Ant Traps

It is possible to purchase boric acid powder, which can be used to create a homemade ant trap. These traps can be very effective against many types of insects, but are especially good with the little black sugar ants that are commonly found in kitchens.

Making your own ant traps can save you a great deal of money and is very frugal, as most of the store bought insecticides are essentially the same thing.

To make your own boric acid ant traps, mix about 1 teaspoon boric acid, with 10 teaspoons sugar and 2 cups of water.

Next, spread the mixture on cardboard or absorb it onto cotton balls. Leave the ant traps in areas where the ants are present, who will then take the poison back to their hive.

Tips for Making and Using Your Homemade Boric Acid Ant Traps

  • When making your own boric acid ant traps, it is important to use them away from small children and animals.
  • Finding the right mix of boric acid is also important, because too much will kill the ants before they reach the hive, but too little will not be effective.
  • It is also important to remember to continue to place the ant traps over the next week or two, even as the number of ants decrease. On the first few days, you might see a flurry of activity, which will then drastically decrease as the ants or other insects are effected by the poison.
  • You need to continue placing the ant traps, so that the entire hive is affected. Often, this will wipe them out for an entire season.
  • The powder itself also has a number of other uses and can be applied to kill fleas, as well as repelling insects.

So, Why Does Boric Acid Work on Insects?

In insects, boric acid affects the body differently, making it a very effective insecticide. Boric Acid was first registered as an insecticide in the US in 1948, but had been used prior to this for some time.

When an insect consumes boric acid, it poisons the stomach and affects the insects metabolism. The powder is also abrasive, further effecting the exoskeleton of the insect.

One of the reasons boric acid is so effective at controlling ants, especially sugar ants and other common household bugs, is that a poisoned insect brings the poison back to their nest, where it spreads to the other insects.

So, Does that mean Boric Acid is Safe for Humans and Animals?

No, boric acid can still be very dangerous to humans, animals, and children. It may requires a lot of it for a lethal dose, but there are also several side effects of exposure to boric acid.

Many of the insecticides that contain boric acid will contain a sweetener, such as sugar, to attract insects. These should be stored and used well away from areas where children or pets will be exposed to.

Other Uses of Boric Acid

Aside from controlling insects, boric acid has many other uses.

Boric Acid is often used in the medical industry as an antiseptic, on wounds, and as an eye-wash. It is also used to preserve wood, in nuclear plants to help control fission, and as a lubrication. Boric Acid was also originally one of the main ingredients of silly putty.

Questions & Answers


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    • profile image

      violalanders 6 years ago

      This is informative hub. Thanks for sharing.

    • steffsings profile image

      steffsings 8 years ago from Pacific NorthWest

      My Auntie Vern told me about this many years ago - this was an old fashion cure with proven results - for sure - glad to see this wisdom available here.

    • Alta5656 profile image

      Alta5656 8 years ago from Davao City, Philippines

      Oh boy! Thank you enormously.You saved my day! More power.

    • KyonSOS23 profile image

      KyonSOS23 8 years ago from Nabon

      Borax has many uses in industry food too.It can do food to spring to bounce .

    • brad4l profile image

      brad4l 8 years ago from USA

      Thanks for sharing RNMSN! I think one of the great things about using boric acid for pest control is that you can mix it up in batches as needed...

    • RNMSN profile image

      Barbara Bethard 8 years ago from Tucson, Az

      as a home health nurse I cant count how many containers I've taken to different well,the patients tell their family and so on and the fight goes on/I think for the most part it has meant an increase of educ and a decrease of the pests in the homes

    • profile image

      sbeakr 8 years ago

      Hmm...I can say I learned something today! Very useful information, thank you.

    • brad4l profile image

      brad4l 8 years ago from USA

      I hope it works for you rebekahELLE, ants can be a big pain, especially if they get into your kitchen.

    • profile image

      Opinion Duck 8 years ago

      Good to know, as those little ants keep coming back.

      Thanks for the info..

    • rebekahELLE profile image

      rebekahELLE 8 years ago from Tampa Bay

      thanks for a very informative article about such a pesky subject. I live in florida and must have a 'planet' of ants living in my yard. we can't get rid of them. I don't want to use chemicals on my yard, but I'm going to try setting some traps and see what happens. Thank you!

    • brad4l profile image

      brad4l 8 years ago from USA

      Thanks Jerilee. A lot of people don't know that boric acid can be so effective against those small black sugar ants. Making your own ant traps is a great way to save money.

    • Jerilee Wei profile image

      Jerilee Wei 8 years ago from United States

      An excellent suggestion especially for ants and a lot safer than some of the more expensive alternatives.