Wednesday, January 7, 2015

Snowy Ant Mounds

A dusting of snow on the ant mounds made them stand out like beacons in the tall grass fields.  I took this opportunity to get out and document the abundance of Allegheny Mound Ants, Formica exsectoides, at Blue Jay Barrens.  The larger mounds may contain more than a quarter of a million ants.  When you see clusters of mounds like this, it’s easy to see why the ants are so commonly encountered in the summer prairie.

The mounds are even easier to see in the mowed field.  The largest of the mounds tend to stay active for many years, even decades.  Smaller mounds appear and disappear more rapidly.  A group of ants will sometimes appear and within weeks, build a mound 8 inches high and 16 across.  A few months later, the mound may be abandoned.  I’m guessing that the temporary mound is used as a base from which to exploit a seasonal food supply or to access a new foraging area.

Considering the number of ant mounds in the field, it’s amazing that only a couple received any damage when I mowed.  This view shows about two acres of field with 43 visible ant mounds.  It’s obvious that the ants are a major component of the ecology of this field.

Mounds are most commonly found in the open, but there are a few mounds in the partial shade of the field edges.

Both the near field and the field beyond the trees contain numerous mounds.  Ants can be found anywhere in the grassy fields, but they are rarely encountered in the 60 foot wide band of trees separating the two fields.

The snow highlights a deer trail and a neighboring ant mound.  This mound, just over two feet high and four feet wide, is considered average size for Blue Jay Barrens. 

It’s strange that there are large open areas that are free of ant mounds.  I’m sure that there are certain conditions necessary for the survival of a large ant colony, but even if these fields are unsuited, I would expect to find failed attempts at mound building. Allegheny Mound Ants are certainly in the top ten group of most interesting animals inhabiting Blue Jay Barrens.  Study of this species could easily monopolize my time for many years, but I guess I’ll just have to be satisfied with casual observations while my time is spent dealing with the property as a whole.


  1. It is amazing how these persisted through the mowing. At what time of year did you mow? It looks like they had time t do a bit of re-building afterward.

    1. Hi, James. The mowing was done during early November. I use a walkbehind DR Field and Brush Mower that cuts about a two foot width. With this machine I can mow around the mounds with no damage.

  2. PS - I wonder if some fine details of soil texture or chemistry determine the presence/absence of the ants?

    1. That's certainly a possibility. I suppose there could be a lot of factors coming into play here.