Monday, November 17, 2014

Mowing and Ant Hills

Mowing the fields is made slightly more difficult by obstacles that must be avoided by the mower.  Top of the list is the earthen mound made by the Allegheny Mound Ants, Formica exsectoides.  A mower and mound confrontation is detrimental to both parties, with the ants and mower operator taking the brunt of the negative impacts.  Large mounds that are kept free of vegetation are easy to see and avoid.

Not all mounds are so well groomed.  Some are so much a part of the vegetation that the two are inseparable.  Mounds such as this are nearly impossible to detect.

Most fall into the middle range with bare tops and vegetated sides.  I don’t understand why some colonies keep their mounds vegetation free, while others in seemingly identical locations, allow plant growth to cover the mound.

There is also the occasional abandoned mound that still stands tall and is covered in plant growth.  These mounds are a little more solid than one that is active and can cause quite a jolt when hit by the mower.  These abandoned mounds are often recolonized and rebuilt to their earlier dimensions.

I was pleased to complete the field mowing with only four mound hits.  Two took the tops off of very small mounds, one of which showed no signs of recent ant activity.  The other two hits were glancing blows delivered to medium sized mounds less than 12 inches tall.  The ants have already closed the breaches to their mounds.

Unfortunately for the ants, there are other threats that prove more formidable than my mower.  Something attacked this mound and spread debris several feet into the field.

The ants have made some attempt at repairs, but the cold temperatures have hampered their efforts.  Many chambers are exposed to the air, compromising climate control within the mound.

Exposed tunnels at the top of the mound can allow heat and moisture to easily exit.  I imagine these tunnels have been sealed shut somewhere within the mound itself.  I’ve seen animals nearly take a mound down to nothing and the ants build it right back up again.

Crows have taken to using the mounds as perches as they forage through the mowed field.

They don’t seem to have any real interest in the mound and don’t do any damage.  The only evidence of their frequent visits is a growing collection of Crow droppings.

Most of the vegetation on the mounds appears to be non-native in origin.  The halo around this mound is a mix of bluegrass and fescue, both species that already had a presence in the field.

Several mounds host a mix of exotic species that are found only on the mounds.  These species are mow poised to move into the fields if conditions become favorable.

Hairy Bittercress has just made it to the mounds in the past few years.  This weedy species began by colonizing disturbed ground near the house and barn.  It now seems to be a permanent resident of those locations.  I’m wondering now if this species could eventually present a threat to the winter annuals growing in the barrens.  I’m not sure how the seeds are traveling, but their method is obviously efficient.

I’ll have a few months to visit with these mounds before the tall grass returns to once again hide them from sight.  After that, I won’t see most of them again until the next time the field is mowed.

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