by David Moore
Manager of Technical Services and Board Certified Entomologist
with contributions by Eric Smith, PhD, BCE
Oh what a topic. So, why would I ever want to bring it up for discussion? If you go to the internet, there is so much misinformation on this subject that it’s scary and possibly dangerous to one’s health. To most people, boric acid is considered to be non-toxic but will kill insects, or it has very low toxicity to humans. It is used primarily for the control of cockroaches, but more and more people are using it to control bed bugs because it is inexpensive. In most cases it is being grossly over applied and misapplied.
Borax vs Boric acid: Let’s start with the difference between borax and boric acid. Borax is the basic mineral that is mined from the ground, and it is then refined through processing into boric acid. Borax such as you would purchase and use in the washing of clothes is not refined as much nor ground as fine as boric acid, and it is not labeled for use as a pesticide.
Common uses of Borax:
- Laundry additive
- Hand soap ingredient
- Trace element in specialty plant, garden, and lawn fertilizers
Common labeled uses of Boric Acid:
- Active ingredient in eye drops
Both borax and boric acid must be ingested for their toxicity to be expressed. The possible exception is contact with body fluids such as eye or nasal moisture, but only if it can dissolve in these liquids which is not likely.
- Borax: With the exception of 20 Mule Team Borax, the percent of borax used in formulations is very low. Most formulations are labeled for external use only, and not to be ingested. None of these formulations are labeled for use as a pesticide.
- Boric acid: Boric acid is toxic, it is a pesticide, it is an insecticide, and it can cause serious illness to pets and children if they ingest it. It is a common active ingredient in many pesticide bait formulations and in some dust formulations.
Boric acid to control insects
How it works:
- For insects, boric acid must be ingested to be toxic; it is not a desiccant (does not cause dehydration) and it does not absorb their protective surface oil or wax.
- Sublethal doses often cause sterility in the female insects.
- Bait formulations. Baits usually contain 5% or less of boric acid as the active ingredient. This is because higher amounts are repellent to insects.
- Dust formulations. Dusts usually contain 98-99% boric acid, with the remaining percentage being an additive to reduce clumping of the powder so it will easily flow and spread.
- Properly applied, the dust is barely visible.
- If over applied (i.e., the insects can detect it with their tarsi or “feet”, the palps of their mouthparts, or their antennae), insects will avoid contact with the deposit.
- Insects ingest boric acid dust as they groom to clean their legs, antennae, and mouthparts.
What boric acid will NOT kill
- Insects (and non-insects such as ticks) that have piercing mouthparts and feed on plant juices or blood (e.g., bed bugs, lice, aphids) do not groom, so boric acid does not control them.
- The larva (immature stage) of insects with complete metamorphosis (beetles, flies, fleas, butterflies & moths, etc.) do not typically groom, so boric acid does not control this life stage. The larval stage is often the stage that does the damage (e.g., clothes moths, stored product beetles and moths, carpet beetles, etc.), so control of larvae is essential to eliminate the problem.
- Boric acid should be treated with respect because it is toxic. It is a pesticide/insecticide.
- Boric acid must be properly applied to be effective.
- Boric acid will not kill or control insect and tick life stages that have piercing mouthparts.
- Boric acid will NOT kill/control bed bugs.
- Boric acid will not kill the larval stage of insects.