By | Thursday, February 24, 2011 2 comments

Here in California we have a really problematic little invasive ant called the Argentine ant (Linepithema humile.) They are real pain in the ass. They look quite similar to what we used to call "sweet and grease ants" when I was a kid back in Boston. But as far as I can tell these little invaders from Argentina are nothing but six-legged sweet tooths – grease doesn’t interest them. There are a variety of interests that are concerned about Argentine ants for a number of important reasons – most notably they drive out native species, thereby unraveling an important part of the natural ecosystems. My concerns are much more prosaic: they are major herders of aphids and scale, and, given the opportunity, they get into my kitchen and start going after anything sticky and sweet.

[For those of you that don't know this, many species of ants actively herd various pests that feed on the sap of plants. Insects such as aphids and scale exude a sweet "honeydew" from their abdomens. The ants feed on this, and will protect and defend their herd against predators. They will even move their wards from plant to plant to maximize their yield. Co-evolution. Go figure.]

I have been battling the Argentine ants in my yard for a couple of years now as part of the overall “low-impact” effort to deal with infestations of aphids and scale on my plants. As needed I would go to the hardware store and buy some ant traps of one type or another to put around the affected plants. They seemed somewhat effective, but not 100%. I assume that this is because controlling ants in the great outdoors without a significant broadcast of very nasty chemicals is basically impossible. But, these little traps did assist in managing the pest problem.

A couple of months ago some of these little bastards found a way into my kitchen for the first time [though technically they aren’t “bastards,” they are “bitches,” since all worker ants are female.] I gotta tell ya, when Argentine ants find something they like their numbers are astonishing. I decided it was time to research ant traps further. Around here the most common brand of ant trap is "Grants." Their tagline is, "Grants! Kills! Ants!" As far as I could tell, with Argentine ants, the Grants motto ought to be "Grants! Thrills! Ants!" Other ant traps sold in my area are branded Raid, TAT, Combat, and Terro. I wanted to see if I could figure out which of the different active ingredients in these offerings would best.

Terro ant traps contain a sucrose solution and Borax (boric acid.) Pretty straightforward. Boric acid acts on ants as a metabolic poison. In larger animals it is basically safe and has been used for ages as an antiseptic, antibacterial, and fungicide for humans. It is only harmful if ingested in very large quantities, or administered in small quantities over a long period of time. If you’re looking for something to off your rich uncle, this aint it.

Grants’ active ingredient is Hydramethylnon, a metabolic inhibitor which is claimed to work against Argentine ants, but either it doesn’t, or the bait component isn’t attractive to Argentine ants.

Raid traps contain Abamectin, a nerve toxin which, though naturally derived from bacteria, is pretty nasty stuff. The small quantities in an ant trap are unlikely to cause harm to a large mammal, but with my lovely dog around, I’m not interested.

TAT traps contain Baygon (Methylcarbamate). Baygon is an Acetylcholinesterase inhibitor – again, a nerve poison. As with Abamectin, a large mammal would have to consume a big dose of Baygon to be harmed, but…

Finally, Combat traps use Fipronil. Fipronil is yet another nerve toxin, attacking the central nervous systems of insects. However, it is also the active ingredient in “Frontline,” the anti-flea medication that I already use on my dog. Apparently Fipronil does not affect mammals, because it acts on a nerve receptor that does not exist in mammals (whew.)

OK, that’s was a really long preamble…

Based on my research, the only two ant traps I was willing to touch were Terro and Combat, which, interestingly, were the two that I had found most effective against Argentine ants in my yard (go figure!) But here’s the thing; all of these traps, safe or not, end up being pretty expensive if you are using a lot of them, and I have an endless supply of Argentine ants.

In the course of all this study I kept running into pages on the web describing homemade ant baits. It turns out that boric acid, aka Borax, the primary ingredient in Terro ant traps, is also the primary ingredient in many roach poisons. It is relatively benign, has been around in use for a very long time, and is really cheap. There are two main differences between Borax-based ant traps and Borax-based roach poison. With roaches you just want the insect die – as fast as possible. So roach poisons tend to be 100% Borax powder. You sprinkle it around where the roaches travel, they walk through it, and drop dead. Ant traps contain both Borax and bait. You need to attract the ants to the Borax. Even more importantly, the Borax is quite dilute. You don't want the ants to die right away – you want them to take the poison and bring it back to the nest where it will be fed to the Queen and to all the developing larvae. 100% Borax, while it will create a satisfying little pile of dead ants, won't ever deal with the actual problem: the nest.

Making homemade ant poison turns out to be very easy and astonishingly cheap. I bought the least expensive bottle of 100% Borax roach poison I could find. It was about four dollars for a 1 pound bottle, which should be enough for the next 30 or 40 years. The formula for the bait is approximately 16 parts water to 8 parts sugar to one part boric acid. For a modest quantity that translates to 1 cup water, ½ cup sugar, and 1 tablespoon Borax. It’s easiest to mix if the water is hot.

For outdoor use I got a (non-medical) utility syringe. I just squirt fresh poison mixture into the old traps once in a while (how’s that for reduce-reuse-recycle!) Inside the house (since I don’t have any kids, cats, or pooka’s hopping about that might get into the stuff,) I put small squares of aluminum foil at the back edges of my counters where the ants are, placing a tablespoon or two of mixture on each one. For two or three days there will be an astonishing army of ants endlessly, tirelessly marching to the pool of bait, drinking, and then leaving. It’s actually fascinating to watch. Furthermore, with this easy access sweet liquid, they leave everything else in my kitchen alone. After about three days suddenly the number of ants goes way, way down. A day or so later there might be one or two ants stumbling around looking confused. I usually put these stragglers out of their misery.

Two days ago a new army of ants arrived in my kitchen, but already this virtually-free mixture is doing its work. Thought I’d pass it on to the rest of you.

  • This mixture is not my invention. I take no credit for it – I am just singing its praises. 
  • There are a lot of different recipes online for Borax ant poison. They mostly differ in the concentration of the sugar solution, ranging from 2:1 water to sugar to 1:2. My ants seem delighted with the relatively dilute sugar solution given here. At my home a higher concentration of sugar just wastes sugar and causes the solution to solidify faster.
  • Different types of ants are attracted by different baits. They will also require different amounts of Borax to hit that crucial level that is fatal, but not so deadly that the workers die before bringing the poison back to the nest. You may need to experiment to get the right ratios for the ants in your area.

Bon Appetite!

[Update: I have found the liquid form of my homemade ant poison inconvenient to distribute, so I am now making ant-poison gum drops. Here is my updated recipe.]

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  1. Excellent. Although spring has not sprung in our region, I will use this solution when the annual ant invasion occurs.


  2. Avermectin is much like fipronil and is harmless to animals infact it is used in a competing product to frontline in the same way, for decades. Further its used safely to protect people from river blindness caused by parasites. Not sure where you read otherwise, but I trust the stuff.


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