How to tell the difference between Formica and Camponotus

The most common newbie mistake I’ve seen in identifying North American ants is to confuse Formica (field ants) and Camponotus (carpenter ants).

Both are common, medium-large in size, with a single waist segment. As they are in the same subfamily, Formica and Camponotus have a similar appearance and are easily confused. If you keep your eyes open you’ll find both nearly everywhere you go.

Here’s an identification trick that will work 95% of the time in temperate regions of North America to separate the two genera.

Look at the worker thorax in side view. If the back forms a single, even curve, you’ve got Camponotus:

A continuous profile indicates Camponotus. (Image by Antweb.org)

If the silhouette is broken into two distinct curves, you’ve got Formica:

A profile with two distinct convexities indicates Formica. (Image by Antweb.org)

Wasn’t that easy?

Caveats apply, of course:

1. This trick works to separate only Formica from Camponotus. Many similar formicine genera occur in our area: Lasius, Prenolepis, Nylanderia, and several others. These are usually smaller than Formica & Camponotus, but be aware they exist.

2. In the tropics, some Camponotus species start appearing with a Formica-like profile. Thus, this trick is only effective regionally.

3. To properly confirm an identification, you’ll want to check your ant against the appropriate taxonomic literature using the full suite of diagnostic characters.

To test your new identification skills, have a go at the following ants.

Formica or Camponotus?

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36 thoughts on “How to tell the difference between Formica and Camponotus”

  1. Very nice. While on the topic of ant identification, I don’t suppose there is a nice North American ant dichotomous key that you could recommend for amateurs? Preferably online, but a book would be fine too.

    1. The book to have is ‘Ants of North America: A Guide to the Genera’ by B. Fisher and S. Cover; a very cogent, well-illustrated (diagrams and photographs) key with descriptions of the genera and, in some cases (such as Formica) descriptions of species groups. In terms of free material, check out http://www.antbase.org – there is a HUGE volume of taxonomic literature available for free (generally as .pdfs); you can search by author or taxon. Creighton 1950 (The Ants of North America) is useful for several groups, but must be taken with many grains of salt as much of its taxonomy is out of date – using Bolton’s catalogue to the ants (available at http://gap.entclub.org/) can help to navigate synonymies. AntWeb.org is a fantastic repository of high-quality images, interactive distribution maps, comparison tools, information, and references; if you have some idea of the group or area you’re searching in, check the ‘References’ heading beneath the ‘Taxonomic History’ headings. Often you can take the reference from AntWeb, search for it on AntBase, and have a go! Biggest recommendation is still the first book mentioned, as it is more ‘user-friendly’ than much of the literature available. Good luck anting!

    2. A good starting point may be M.R. Smith’s House-infesting Ants of the Eastern United States. It’s available at http://www.archive.org/details/ants_10395. It includes a key to subfamilies, keys to species, and notes on taxonomic characters and biology for each species. The scope of the book is obviously limited. For example there are no ponerines, sensu lato. Some of the names are out of date, as the book was written in 1965. You may want to check AntWeb for the latest synonyms. The excellent habitus drawings, most by the late A.D. Cushman, are available on a T-shirt from BioQuip!

  2. A dark minor Camponotus sexguttatus from Florida ybeing one exception, as they have a similar (but slightly flatter) profile, making them at first glance look like a small hairy Formica.

  3. 1 Camponotus
    2 Formica
    3 Formica
    4 Camponotus
    5 Formica

    Don’t all Formica have ocelli too and not Camponotus?

  4. I started out confusing Formica with Lasius! I took my first box of ant IDs to the Smithsonian where Dr. David Smith kindly showed me the errors of my ways.

  5. James.C. Trager

    Benoit beat me to it, but I had the same thought about Colobopsis. This differentiation breaks down seriously in some parts of the Tropics, but there are no Formica there anyway. However, it again works nicely in temperate southern Australia for separating Camponotus from the Formica-like genus Notoncus.

    Seems like good future posts would be Formica and Lasius, and then the brown Lasius vs. Tapinoma, two other very common mistakes in ant identification. I feel a field guide in the making…

      1. Terry — The subbgenera of Camponotus are an utter mess. I’ll betchya (gentlemen’s bet, just ot be safe) there’s not a single one that’s monophyletic, unless it’s monotypic.
        Just ignore ’em!

    1. @James, it also breaks down here in the Philippines. We even have a Camponotus that mimics Dolichoderus. Mimicry is rampant: Myrmecina looking like a Pristomyrmex, Nylanderia looking like a Tapinoma, etc. You always have to look closer, lest the ants make you look like an idiot. 😀

      1. I’ve found breaking the groups up as follows to be helpful.

        Group 1 True Camponotus and Tanaemyrmex. These are all on the larger side of the spectrum. Size ranges from 6mm to 20mm long.

        Group 2 Myrmentoma, Myrmobrachys, Myrmothorix, and Myrmosphincta. These are basically smaller version of Group 1. Often the largest majors are only 7mm long, or certainly less than 10mm long.

        Group 3 Colobopsis and Myrmaphaenus. I call these door ants because the queen and largest majors all have flattened heads which are used like doors. These are small as in Group 2.

  6. Danny McDonald

    Also, the antennal sockets of Camponotus are set back from the margin of the clypeus, whereas, Formica’s antennal sockets are set right on the margin of the clypeus. However, this is nowhere near as obvious as the characteristic you pointed out. Love the comparison, and would like to see more! Maybe Linepithema humile and Forelius or Tapinoma sessile?

    1. I second that!

      As not really a myrmecologist, it would be nice with some introductions of the higher taxonomic branches of Formicidae 🙂

      /Alex

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  12. I can identify Lasius, Camponotus, and some other native ants in my area but I always get tetramorium immigrans and Formica queens mixed up

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