Are there army ants outside of San Diego? Spenser, California, USA


Dear askantweb,

I found what seems to be an undocumented army ant while camping in San Diego County.

Doing my best to remember, I recall these characteristics of the species:

Morphology:

  • Completely black
  • Worker, major worker, and soldier classes
  • 5 cm to 10 cm long
  • Soldier mandibles appear to be able to make an audible snapping sound

  • Behavior:

    • Forms columns at night moving in one direction
    • What seems to be scattered scouts mostly of the worker class preceding the main column mainly observed just after sunset
    • Invades the local termite colonies
    • A number of ants were found to be dedicated to what appears to be guarding an entrance of apparently a subterranean nest at the base of a tree. This was observed during the day and the only instance of observing this specie during the day except when excavating a known local termite colony which was being attacked or occupied by these ants.

    Though it could simply be a carpenter ant, please advise or forward to anyone who may be interested. Thank you.

    Sincerely,
    Spencer
    ****************
    Dear Spencer,

    If the insects in question are really 5-10cm long, it's pretty unlikely that they're ants. We have a blog post on how big ants tend to get, and California I can't think of any ants that would be much bigger than 2cm, even if they were a queen.

    There are actually quite a few documented species of army ants from California. The genus Neivamyrmex has workers of different sizes, but they're kind of continuously polymorphic, so you'd be unlikely to think of them as "worker" "major worker" and "soldier." I have a little bit of experience with army ants from the tropics, and I've never heard them really snap.

    The only genus I've heard make an audible snapping noise is Odontomachus, seen here closing its jaws. This genus hasn't been recorded from California as far as I know, but it's possible that the species found in Arizona could make it in SoCal. However, these ants are all the same size as each other, so you wouldn't have noticed distinct castes.

    Carpenter ants, (genus Camponotus) are also large and polymorphic. If you were close to a lot of them, you might have noticed a vinegary smell (formic acid). None of the other ants I've just mentioned would have made that smell.

    Ultimately, I guess I'm stumped. If you go camping again, be sure to take some pictures!

    Best,
    Jesse Czekanski-Moir & the AntAsk Team

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