Wednesday, January 25, 2012

Ant Mound Predation

Ant mounds, built by the Allegheny Mound Ant, Formica exsectoides, suffer a bit each year from foraging animals seeking potential food items buried in the mound.  Usually it’s just some shallow digging that does little damage to the integrity of the mound.

The animal that did this must have been more ambitious than most.  There was quite a pile of dirt brought up from this hole.

The opposite side of the mound showed an even more aggressive excavation.  I don’t know what the animal was after.  There was no evidence of anything edible in the spoil or left inside the excavation.

Crumbs from the digging are still perched atop the nearby Indian Grass stalks.  That means it was probably done last night.  Heavy rain the night before would have quickly washed this evidence away.

This explains all of the dirt piled outside the holes.  The excavation goes completely through the mound.  There was still no evidence of what motivated the animal to do this much work. 

These galleries would have been filled with ants during the summer.  In January, the ants are normally not active outside the mound, but depending on temperatures and sunlight, are often present within the mound.  I’ve read that winged queens sometimes overwinter in the colony and winged queens seem to be a treat for any animal.  Foraging animals don’t just dig for the fun of it, so I’m sure there was something worthwhile to be found here.  I just couldn’t find a clue to what it was.


  1. To my knowledge, no Formica species has either brood or winged ants in the nest over winter, though this is common in a number of other genera, particularly carpenter ants. I too am not sure what made the excavations in your picture, nor what motivated it to dig so far in.
    Around here, I often see flickers drilling into ant mounds, particularly as warming weather in late winter brings the ants nearer the surface. And then, as if to add insult to the injury of eating the winter-slowed and essentially defenseless ants, the flickers leave droppings packed full of undigested ant exoskeletons on top of the mounds.

  2. Thanks for the information James. The flickers around here also spend a lot of time digging into the mounds. I haven't seen any droppings with ant exoskeletons. I'll have to look for these.

  3. looks to me like Red or Grey fox diggings but i dont know what the attractor would have been .

  4. Hi Mike. That's a possibility. I've seen Gray Foxes in the area recently.