Friday, July 20, 2012

Fire Ant Mystery in Harris County, Texas

While checking my email Monday I received this report from Sean McGuire in Harris, County, Texas:

“I ride my bike on a concrete bike trail between Pasadena and La Porte along Fairmont Parkway.  I've notice several times, especially during wet weather, that fire ants will form long trails down the trail.  Not too unusual, except that they seem to exactly follow the tire tracks of bicycles - picture the muddy track that a bicycle would make if it had gone off in the mud then tracked the mud down the trail including where the front and back tire separate in a turn.  Except that is not the case - the concrete is clean, just long trails of fire ants.  I can only think that the bicycle tire leaves behind some unseen trail or scent that the fire ants follow.  The other unusual thing is the mass quantity of ants and how far they follow the tire track - at least 1/4 miles or more.  Again they perfectly follow the apparent unseen track of a bicycle. 

I've attached a picture.  Just curious if you have seen anything like this or could explain this behavior.

Sean McGuire”

Photo of fire ant foraging trail on bike path

Additional view of fire ant foraging on bike path

Closer view of fire ant foraging trail on bike path
Wow, what an interesting observation.  Thanks Sean for recognizing this as an unusual phenomena and documenting it for us.  It does appear that the ants were attracted to the path of the bike tires for some reason.  

 This email was passed along to several researchers who are an authority on fire ant behavior. 

Dr. Bradley Vinson, Professor, Department of Entomology, Texas A&M University, College Station, TX replied:

“It does look like the ants are following a trail. What is interesting to me is that they are following the edge of the bike tires rather than the center. It would appear that they are following an odor or contact chemical trail. It would be interesting to pull a bike tire across a pavement and see if ants follow it. But tires from different companies might or might not have the same chemicals. Also the tire that led to the trailing could have gone through something that contaminated the tire and this would likely lead to 2 parallel trails (something on the side of the tire). It appears to be really attractive; a lot of fire ants are out on the trail.”

Dr. Bob Vander Meer, Research Leader, Imported Fire Ant and Household Insects Research Unit, USDA, Agricultural Research Service, Gainesville, FL, replied:

“That is an impressive photo!!! A while ago there was interest in fire ants being attracted to rubber bands used to hold newspapers together. Consistent results were hard to get so the mini-project was abandoned. A similar episode occurred when it was observed that fire ant workers followed a trail made with a ballpoint pen. So, it is possible that compounds in bicycle tires are influencing fire ant behavior. Maybe a colony was caught in migration mode and became trapped by the irresistible smell of tire residues on pavement! The number of ants suggests colony migration.”

Foraging fire ants respond to various odors.  In fact they use odors (pheromones) for all kinds of communications.  A simple explanation of this communication activity can be found here: 

and here: 

Fire ants use their stingers to periodically mark the ground and leave a chemical pheromone trail:
  •     To mark trails to food
  •     To mark trails home
  •     To recognize their queen
  •     To recognize other worker ants from their colony
  •     To alert the other ants of danger or intruders
  It would appear from this photo that some foraging ants were attracted to an odor that was on the tires of the bicycle.  Who knows what is was, but they were attracted to it.  Once they started following the trail they laid down a pheromone trail for other ants to follow.  The original attractant may be long gone, but the pheromone trail remains, and intensified as others ants pass.  With the rains we have had recently in the Houston area, the fire ants could be migrating to a higher area and the cement bike trail is a perfect highway to do this on.

Informational video on fire ants moving a colony from eXtension site: 

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