What are these small ants in walls of my house? (Sarah, NE Texas, USA)


I am battling hordes of very small ants in the walls and under the floor of an old house. They are too small to be carpenter ants or fire ants.

They instantly find any food and get into containers I would have sworn were unassailable. I tried to ID them, but every ant species I thought might be them is said not to sting or bite - and these DO.

They don't raise a huge welt like a fire ant, but it is a very distinct sharp needle-like prick. I haven't managed to stop myself from slapping at them in time to see if it is a sting or a bite. They are quite small (1/12th of an inch, maybe? tops?) and translucent orange in color, with a slightly darker brown dot on the posterior.

I also get very large solid black ants in one room of the house - also from under the floor or through the wall.

Any idea what they are?

Dear Sarah,

I'm sorry to hear about your problem. Normally I enjoy watching ants go about their daily activities, but I have also had some experience with tiny stinging ants like the ones you've described, and I would want them out of my house, fast.

So, first things first, there are some measures you can take before you call the exterminator. We describe how to get rid of ants in your home here.

Second: What are these ants? There are three species I can think of that more or less fit your description that have established reputations for themselves as world-wide pests. They're all stingers, so no need to stop slapping:
Monomorium pharaonis,
Monomorium destructor,
Wasmannia auropunctata.

Monomorium destructor might be the easiest to tell apart from the other two. Its workers are conspicuously polymorphic; that is, when you see a lot of workers together, there will be some that are different sizes. The largest workers will be almost twice as big as the smallest workers, and there will be workers of intermediate sizes. They are usually orange-brown in front with a darker gaster (the gaster is the last major part of an ant's body). Monomorium destructor earned their species name because in addition to having a painful sting, they are very good at chewing through things like plastic bags, clothing, and even the insulation around wires. If you notice a lot of holes in things near where the ants are, then there's a good chance you have these ants.

Under a microscope, it's easy to tell the remaining two ants apart. There are numerous differences, perhaps most obviously the large spines Wasmannia auropunctata has projecting off the back of its mesosoma (the middle body section of an ant). Without a microscope, however, it can be difficult to distinguish the two. If you saw them side by side (or fighting!), you would notice that Wasmannia has a shorter, more square body shape, and is about the same color throughout its body. Monomorium pharaonis has a longer, more slender shape, and it usually has a darker gaster, but on both ants the color can be variable - Wasmannia can have a dark gaster, and M. pharaonis can be all the same yellow-brown color. Wasmannia auropunctata is sometimes called the "electric ant" because of its uniquely scintillating sting. Unless you're a real connoisseur of ant stings, though, it might just feel like another painful annoyance.

Looking at the pictures I linked to on the web might help, but really the best way to get a confident identification of tiny ants is with a microscope or a very, very close picture.

As far as I know, of those three ants only Monomorium pharaonis has been reported from Texas (based on the list published on AntWeb here, and an older list by Wheeler and Wheeler here), but Monomorium destructor and Wasmannia auropunctata are both very good at dispersing with humans. You haven't just come back from a fun trip to a tropical island by any chance, have you? Both Wasmannia auropunctata and Monomorium destructor can be quite common in Southern Florida and the Caribbean.

I hope this helped.
Jesse Czekanski-Moir & the AntAsk Team

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