• Hannah Moloney

How to kill Cockroaches using Boric Acid

Updated: Feb 15

I live in Coral Bay on the Ningaloo Reef. My little caravan-park style house can be found surrounded by other matching caravan-park style houses in Pleasant Ville (yes real name). All 38 houses are built using the exact same housing plan, look sickly white & all have matching furniture. Wetsuits dangle from the rope clothes lines on the front porches, chairs are made out of milk crates and coffee table are nailed together using old wooden pallets. Living in the middle of no-where in a coastal desert with a highly transient community, probably doesn’t help the insect problem.

“Little boxes, on the hillside. Little boxes, little ticky tacky littles boxes…. on the hillside and they all look just the same”

When I say we had a cockroach problem, I’m not over-reacting. It wasn’t just a couple of roaches hanging out under the sink. It was a couple of roaches who had hundreds of babies, who then had all their friends over for an unsupervised under-agers party with free booze. These party roaches all had unprotected sex and each had an unplanned family. My house was their home and they provided for their families using the food in my cupboards.

This ecosystem of cockroaches included baby roaches to huge mumma roaches who looked like they could carry you away in your sleep. As out of control as it was, I still refused to use a chemical heavy roach bombs and opted for a natural alternative. Boric Acid (diatomaceous earth) seemed to be a safer, eco-friendly, less poisonous to human option than the ones on the shelves in my the local supermarket.

Using the recipe for Boric Acid bait balls that I found on their website, I started a mini science experience on my back porch. Once the balls dried, I scattered them throughout my food cupboards, beside the fridge and microwave, under the kitchen and bathroom sinks. With immediate noticeable changes in cockroach populations and less roach poo on my shelves, the bait balls must have been quick to work. Within a few days we were finding next to no small roaches in the daytime, and only a few small roaches when we turned the lights on a night.. The large mumma roaches were drowsily roaming the floor tiles looking like they’d had a few too many tequilas. Within a week, I was lucky to see a roach at all.


Roaches multiply fast & quickly and become immune to the insecticides sold in supermarkets. The longer you use these commercial posions, the less effective they become. Boric acid is odourless & tasteless and doesn’t lose potency over time, meaning they don’t develop a resistance or a disliking to it.

Boric acid works first as a stomach poison and secondly by wearing out the waxy external coating on the cockroach and causing it to dehydrate.

When using it in the powdered form, they walk through it getting it stuck to their feet. Similar to cats, cockroaches groom themselves, in turn ingesting the powder. By using bait-balls (like I did) they are attracted to the onion, ingesting directly. Soon enough their internal systems accumulate enough of it to kill them.

What is boric acid?

Boric acid is a low-toxicity mineral with insecticidal, fungicidal & herbicidal properties.

It is the “secret ingredient” to many commercial insecticides.

It acts as a insect killer by removing moisture from the body causing severe dehydration and eventually death. It is odourless and neither an attractant nor a repellent, so the insects will keep coming back to treated areas. While it is not as fast acting like synthetic pesticides, it doesn’t pose the same health concerns and remains highly efficient over a long amount of time. Within 2-3 weeks you should start to see some results and it can take up to a month to spread through an entire colony.

Is it harmful to humans?

It has a toxicity of that close to table salt. It is fairly harmless to humans and pets when used accordingly. However that doesn’t make it safe! Always use gloves and do not inhale or consume.



200g x boric acid (I bought the 400g container for $10 online)

1 x medium onion (finely chopped)

1 x cup flour (+ more if balls are too soft)

1/4 tsp salt

About 100ml milk (add only as needed, I put way too much milk in!)


Metal or ceramic bowl (don’t use plastic, wooden / anything porous )

Mixing spoon (nothing porous)

Kitchen gloves

Baking paper

Egg carton



  • Have all ingredients ready as once you start mixing, your gloves will have sticky dough on them containing boric acid.

  • Mix together finely chopped onion, boric acid, flour & salt. Use enough milk so the mixture forms a dough.

  • Roll into 1-2cm balls. The larger sized balls are a bit more efficient and last longer as there's more onion in them. The smaller ones are good for tight places!

  • Put the balls on baking paper and allow them to dry (15 mins). Mine took hours because I went a little overboard with the milk! And because mine were so soft and sticky, I put all balls in a cut-up egg carton. But this also means they are easily moved and roaches are attracted to the cardboard too (bonus?).


Back of cupboards

Behind fridges

Under sinks

Behind dishwasher (if you are a lucky human)

Around rubbish bin

Under bathroom sinks

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