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.

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.

Spider Posing as an Ant

It’s interesting how many creatures have appearances and behavior patterns that cause them to mimic other species.  I love to find such creatures.  Many cause me to do the classic double-take as I dismiss them as something common and then snap my attention back because of some little thing that didn’t seem quite right.  This little fellow had me doing just that.  It’s part of a group of spiders considered ant mimics, meaning that many organisms mistakenly consider them to be ants.

Since I see these spiders fairly often, I assume them to be common at Blue Jay Barrens.  Their mimicry is less effective when they are at rest, but they are seldom still.  They move as a foraging ant moves, scurrying around the surface of plant leaves or chasing back and forth across a patch of bare ground.  When they do stop, they move their front legs in a manner similar to the movement of ant antennae. 

This is a Castianeira species and it does an excellent job of masquerading as a large black and red ant.  In most cases, animals will mimic a species with superior defensive capabilities.  It seems that both ants and spiders are equally equipped with weaponry suited to dissuade attackers.  Maybe the spider benefits by evading the notice of some predator that specifically seeks spiders.

Here’s the model for the mimicry.  When in motion, the spider is almost indistinguishable from Formica exsectoides, the Allegheny Mound Ant.  The Mound Ant is here in abundance and is to be found foraging on every stationary object in the landscape.  They are so plentiful that ant mimic spiders easily blend in as part of the throng.  It’s just a joy to observe an oddball ant and have it turn out to be an ant mimic spider.

Giant Ragweed

Weather has been a dominant force in the cycle of life at Blue Jay Barrens this year.  The range of conditions from flood to drought has disrupted the ordered flow of most seasonal events.  Drought continues to be the single most influential event of the year.  A recurring theme across the landscape is the reduced size of most plants due to lack of moisture.  Giant Ragweed is no exception, with the plants being about half their usual height.

The water starved plants try to rebound overnight, but there’s too little available moisture in the soil to do the plants much good.  Wilted leaves droop pathetically during the day.  Perhaps the hurricane remnants will pass through and help alleviate our water deficit.

Despite the dry conditions, the plants are blooming profusely.  The green and yellow flowers surrounding a tall spike at the top of the plant are hardly noticeable. 

Giant Ragweed produces separate male and female flowers.  Those flowers crowding the spike are all male and release a massive dose of airborne pollen.  Hay fever sufferers would definitely not be pushing in to get a close-up of these flowers.

Giant Ragweed is a native annual, so the plant must produce seed to ensure a future generation.  Female flowers are found concealed in leafy bracts growing from the leaf axils at the base of the flower stalk.  Most people don’t even notice these well hidden flowers. 

Typical Giant Ragweed leaves are three lobed like the one shown to the left above.  Many of the Blue Jay Barrens population are unlobed.

On of the most interesting features of the Giant Ragweed is the interaction between the Allegheny Mound Ants, Formica exsectoides and a Treehopper, Publilia concava.  Clusters of these insects are found on almost every plant.

The Treehoppers feed on ragweed sap and as a byproduct of the feeding process, produce honeydew.  The ants feed upon the honeydew.  In their efforts to protect their food supply, the ants provide security for the Treehoppers and the Giant Ragweed plant.

The Treehoppers are fascinating creatures.  The spiky nymphs exhibit a two-tone color pattern that is variable between individuals.  They certainly don’t look like something that is a likely food item.

The adult Treehoppers have a smoother appearance.  They stand out against the bright green of the leaf, but their wide variation in color patterns makes them appear to be a part of the plant.  These adults will overwinter in the leaf litter at the base of the plants and will emerge next spring to mate and begin new colonies.  I hope to always have a nice patch of Giant Ragweed for their use.

Energetic Ants

Soil temperatures are warming rapidly and this has stimulated the Allegheny Mound Ants, Formica exsectoides, to almost frantic activity.  Damage inflicted upon the mound over winter is being quickly repaired.  This particular blemish was created by a deer that chose to go over the mound instead of around.

Some late winter mounds support a covering of green growth composed primarily of non-native plant species.  Kentucky Bluegrass and a variety of mustards make up the bulk of the growth.  Some colonies tolerate the vegetation on the mound, while others will have the mound cleared of all greenery by mid summer.

Judging by the rate at which debris is accumulating, there must be some major excavation going on down below.  The grass plants are already becoming buried.

Some large loads are being brought to the surface.  This piece was too heavy for a single ant to lift and had to be drug out of the way.

At some holes the ants formed a ring at the entrance, all facing into the mound.  This didn’t seem to fit any logical defensive strategy.

It turned out that those ants were waiting to receive excavated material from ants inside.  The receiving ants carried the material away to be discarded.  They would then return to the hole and wait for more material to be passed up.

I didn’t notice any ants foraging away from the mound, but I did find a group working to drag a cranefly larva up the side of the mound.  If the temperatures remain warm, ants should soon be moving out into the field in search of food.

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.

Death of a Super Hill

I was sad to see that the largest ant mound at Blue Jay Barrens has been partially abandoned and is in a state of decline. I know that this happens to many mounds, but I was hoping the Super Hill would continue to grow. There’s always the chance that the ants will reclaim the mound later and bring it back to its previous glory.

Instead of one super hill, there are now several mounds looking much like a string of volcanic islands. I assume that they are populated by ants that were all once a part of the super hill. There are ant highways along the ground that connect the mounds and the ants show no signs of conflict. The super hill has been in existence for about 15 years and has survived a wide range of weather conditions. I don’t know what could have happened this year to cause such a change.

The super hill hasn’t been completely abandoned. There’s still activity about equal to what you would find in a medium sized mound.

The new mounds are growing rapidly. The grass that appears to be growing at the bottom slope of the mound is actually the tops of plants that have been partially buried by the expanding mound. Mounds formed from a colony split grow at an incredible rate. This spot was all grass in the spring, but in a matter of only a couple of months there’s a 30 inch pile of soil that has smothered the plant growth. This is just another example of change and diversity on the prairies.

In the opposite direction, I’ve been seeing flocks of Nighthawks passing over from the west every evening for the last week. A strung out flock of about 50 took around a minute to pass over yesterday evening. If you stop to watch birds fly over, I would recommend moving away from any ant mounds. Before the last bird was out of sight, I had an ant chewing on my ankle.