Urban Ants of the Midwestern United States

Spring is springing here in the midwest and the ants have tunneled out from their winter hibernation. The start of anting season is the perfect time to present a guide to the common urban ants of the region.

This post does not show all the ants from the midwest (you can find a comprehensive list here). Rather, these are the most abundant species active above ground in urban gardens, sidewalks, and homes.

Odorous house ant, Tapinoma sessile

Ants found in midwestern houses are more likely to be Tapinoma sessile than any other species. These are small brown ants with single small waist segment and a distinctive cheesy odor when crushed.


Pavement ant, Tetramorium species

Tetramorium species ("species E" and tsushimae) are common sidewalk ants introduced from Eurasia, and our only common non-native ant. Pavement ants are medium-small, with two waist segments, and hold sprawling battles to establish territorial boundaries, especially in spring.

Acrobat ant, Crematogaster species

Crematogaster is unmistakable for the heart-shaped gaster that can be raised above the body. Acrobat ants (Crematogaster cerasi {pictured}, and C. lineolata) are commonly seen tending aphids for honeydew.

Little black ant, Monomorium minimum

Monomorium minimum is a tiny, slender, shiny ant with a two-segmented waist. These are common ground-foraging ants, but their small size renders them hard to see.

Thread-waisted ant, Aphaenogaster species

Species of Aphaenogaster (especially A. rudis & A. fulva) nest in soil or rotting wood in shaded lawns and parks. They are reddish brown in color with a slender, two-segmented waist, and are generalist scavengers important for the dispersal of the seeds of several native plants.

Thread-waisted parasite ant, Aphaenogaster tennesseensis

Aphaenogaster tennesseensis queens start as parasites invading nests of other thread-waisted ants, eventually replacing the colonies with their own offspring. Worker A. tennesseensis are similar to other Aphaenogaster species but have a broader head and a shiny red gaster.

Acorn ant & crevice ant, Temnothorax species

Temnothorax shaumii (left) and Temnothorax curvispinosus (center) are small ants with a slender, two-segmented waist. An Aphaenogaster thread-waisted ant (at right) shows the relative size. Temnothorax nests in tiny spaces like old acorn husks and crevices in rocks and tree bark.

Thief ant, Solenopsis molesta

One of the smallest midwestern species, Solenopsis molesta is a tiny, elongate, light reddish-brown ant with a two-segmented waist. Thief ants live underground but sometimes enter houses or forage along sidewalks.

Eastern black carpenter ant, Camponotus pennsylvanicus

Camponotus pennsylvanicus is the famous black carpenter ant, perhaps the most damaging pest species in our fauna for its habit of nesting in decaying or water-damaged wood of older houses. Black carpenter ants are large, with a single waist segment, and a light coat of golden hairs on the gaster.

Red-banded carpenter ant, Camponotus chromaiodes

Camponotus chromaiodes is similar to the black carpenter ant, but with red on the back of the thorax, legs, and front of the gaster.

Small carpenter ant, Camponotus nearcticus

Camponotus nearcticus is like a smaller, shinier version of the big carpenter ants. This variable species can be all black or various combinations of red and black.

Chestnut-colored Camponotus, Camponotus castaneus

Camponotus castaneus is among the largest ants in the midwest, light reddish-brown in color with a single waist segment. Unlike other Camponotus, C. castaneus nests in soil rather than wood. This species is commonly seen at night or on cool, cloudy days.

Silky field ant, Formica subsericea

Formica subsericea is a common soil-nesting ant in midwestern lawns. It is medium-large, with a single waist segment, and black with an obvious silvery sheen.

Slender field ant, Formica pallidefulva

Formica pallidefulva is a common soil-nesting ant in urban lawns. This species is somewhat shinier and more slender than the silky field ant, and slightly less hairy than the very similar uncertain field ant. In Illinois, F. pallidefulva tends to be dark, but color varies over the range of the species.

Uncertain field ant, Formica incerta

Formica incerta is a medium-large, single waisted ant. It is slightly hairier than the similar F. pallidefulva and tends to inhabit more natural settings.

Slave-raiding ant, Polyergus species

Each common species of Formica field ant is plagued by a Polyergus parasite (P. montivagus is pictured here) that steals brood during spectacular afternoon raids. The pilfered ants emerge in the Polyergus nest and perform all the foraging, nest construction, and brood care. Slave-raiding ants are recognized by their pointed mandibles and reddish color.

Sidewalk ant, Lasius neoniger

Lasius neoniger is a medium-small reddish-brown ant with a single waist segment and a rather fuzzy vestiture. Sidewalk ants leave conspicuous piles of excavated soil around their nests.

Winter ant, Prenolepis imparis

Prenolepis imparis is easily recognized as a shiny brown ant, medium-small in size, with a large pointed abdomen. They are superficially similar to acrobat ants (Crematogaster), but have a single-segmented waist. Winter ants are most active in cool weather and often disappear during the hottest months.


31 thoughts on “Urban Ants of the Midwestern United States”

  1. Are the two spines on the rear part of the thorax of the Aphaenogasters diagnostic, or do other ants have those as well? I’ve been trying to identify the most common ants I’ve been seeing around Albuquerque, and I know they have those spines. They often have black heads, thoraxes and legs, and red abdomens.

    1. Many ants have spines on the propodeum- not just Aphaenogaster. Your description puts me in mind of Pogonomyrmex rugosus, a harvester ant. Note that the gaster color of that species varies, so that it is sometimes black, or sometimes red to nearly yellow.

      1. Wow, I think you are exactly right. They even have the same “beard” hairs I’ve seen, but forgot to mention. Now when I see them again, I can say “Ah yes, Pogonomyrmex rugosus.” Assuming I can remember that and pronounce it correctly, of course…

  2. I loved the wedding photos (so glad you shot B&W!) and it might eventually be a post that links to ‘aunts’.

    Thanks for identifying the Oderous House Ant for me previously (the one my cat eats and rolls on), but my absolute favourite from this post is the Uncertain field ant.

    I think there’s a children’s book here!

    Lovely images, as usual, and thanks so much for introducing me to some of the complexities of the little creatures that I merely try not to step on. (Except some of the carpenter ants who live in my garden fence: I seriously avoid them.)

  3. Great link and photos, Alex. Ants are fun to look at.

    I vote for Pyramica pergandei as the most photogenic ant of Illinois !

    Wierd ‘setae’ on the head and what is the fungus-like “stuff” on the petiole and abdominal segments of members of this genus for ???

    1. I’m not a fan of common names either as they are too often only vaguely descriptive. For example, why are Crematogaster sp. not called “heart-assed” ants?

  4. Nice little intro to the most commonly encountered ants of our region. I would only add Lasius claviger, not uncommonly encountered by folks digging in their gardens.

    Gordon and Josh are such curmudgeons! “Uncertain field ant” is priceless, especially since most folks, even myrmecologists, remain somewhere between quite and totally uncertain about it. I don’t really see the problem with it. Also, I think Lasius neoniger is typically called the cornfield ant.

    1. I thought about both Lasius claviger (and Ponera, and Brachymyrmex), as these species are dirt common in the midwest, but decided I’d stick to just those ants that are generally seen above ground, without digging. Perhaps, if the consensus is otherwise, I’ll add them to the gallery.

    2. I’m not so much a curmudgeon, as someone that would like to see more accurate application of common names. Mark Deyrup’s attempts to develop common ant names (and for that matter, Alan Andersen’s) are more in-line with what I think are practical common names.

      Instead of a “trap jaw ants,” we can have the “rough petiole snapping ant,” the “Florida scrub snapping ant,” and the “southeastern snapping ant.” Etc., etc.

  5. A great list! But I’ve never thought of Polyergus as abundant in urban areas. Perhaps you could also add Ponera?

    1. I hadn’t thought so either. But if you walk the Urbana sidewalks during any late afternoon in the summer, Polyergus really are one of the most common ants here. I love it!

      1. I think I’ll convince my friend to collect some Polyergus in addition to those Brood XIX cicadas…he’s coming to Urbana-Champaign! (not for entomology though.)

      1. And don’t forget New Mexico! I see so many pictures from Arizona and Texas, but you should stop somewhere in between sometime! : )

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