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Ficus disruptus - When Ants Take Over an Indoor Fig

Q. "We have a Ficus benjamina, which is large enough for our cat to climb. I have noticed that small ants are also climbing it as well as living, I think, in the soil. The tree hasn't been outdoors, and although several online sites mention the possibility of aphids attracting the ants, I see no infestation other than some sticky sap on the stone floor where there didn't used to be any. I also see little whitish blobs of sap on many of the leaves, where, I'm guessing, the ants have nipped the leaf to let the sap ooze out.

"I've used Terro brand boric acid bait traps for weeks with no diminishment, although many ants have taken the bait. I think that they go outside at times, because on an outside windowsill I see what I'm guessing is ant "dirt," which reappears each time I sweep it away. The tree is much too large and heavy to completely immerse the pot in water, as suggested online. Have you any ideas? The tree is in a heated room and looks healthy in spite of its guests."

    ---Carol in Wynnewood, PA

A. Those of you who've been with the show a while can probably make one big observation here, right?

    Yea-Ahhh; she does have aphids!

And so does her Ficus {rim shot}. Thank you; thank you; I'm here all week; don't try the veal; it's very nasty. Anyway, her Ficus named Benjamin is a type of non-fruiting fig tree that is among the most popular houseplants. And that sticky stuff is not ant-nippings; it's the aphid's "honeydew", a very polite synonym for their "frass", which itself is a genteel way of saying bug poop.

Anyway, the shall-we-say 'secretions' of sap-sucking aphids are sweet, and so ants actually 'farm' the little insects, like Minnesotans do dairy cows, protecting them in exchange for the sugar-rich food they produce.

So which came first? The aphids or the ants?

I suspect the former. A couple of aphids entered the house on a new plant or some such and got onto the Ficus. A worker from a nearby colony of ants discovered this equivalent of an unlocked candy store, the ants went to work protecting their little charges the same way they do on roses outdoors, and the grateful aphids have now multiplied enough to support a big ant colony.

And the aphids aren't coming and going out that window, so the evidence suggests that the main ant colony is outside.

Now, we confirmed that Terro ant traps still use a low dose of boric acid as their active ingredient; and as we have explained in previous Questions of the Week, low dose boric acid has been the non-to-low-toxic ant control of choice for decades. So: why are these usually reliable boric acid traps not working?

Who knows? Maybe the worker ants are taking so much honeydew back to the colony that there isn't enough boric acid getting through. (Aphid poop IS probably preferable to sugar water if you're an ant with good taste.) No matter what, controlling the aphids is job #1 here. And to do that, she's going to have to really clean up those leaves. I'd start by wiping them down with a wet washcloth and then using a pressurized sprayer, paying extra attention to the undersides of the leaves. (Have a helper hold a towel behind the plant to keep the area around it from getting wet.)

Then repeat! Wait a few days and do it again. Yeah; yeah—I know she says she doesn't see any aphids. But I'll bet she'll see the squished evidence on that wet rag.

Now the ants will be getting testy; their herd is being decimated. They just might even stop coming by if dinner is no longer being served. But there's also a new type of ant bait to try.

Boric acid has long been the organic standard, but I was at the website of a certain company that supplies natural garden products (whose initials are "GA"—and it's not Green Arrow!) and noticed that the active ingredient in their ant traps was now spinosad and not the boric acid they previously used. So I suggest baiting any leftover ants with some of these new spinosad traps.

Now: a reminder for those what know and a primer for those what don't: what exactly is 'Spinosad'?

Technically it's plural—as in Spinosad-s. Like Bt, there are several different strains of this helpful organism, but unlike Bt, where every strain is VERY pest-specific, natural pest-control products typically contain a combination of Spinosad strains.

Where does it come from?

Rum! The basic bacteria were discovered in the soil of an old rum factory in the Virgin Islands. The modern insecticide is made by combining two strains of the fermented bacteria.

Now, in addition to switching to these new traps, I also advise our listener to wipe up nearby surfaces as well as plant leaves. Our old friend Bill Quarles, head of the Bio-Integral Resource Center in Berkeley, California taught us years ago that ants produce and follow chemical-like trails on their foraging. Wiping down the areas between the plant and that window will discourage them from coming back inside from the outdoors.


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