Fire Ants Catch a Little Sun

It is early afternoon on February 19th, and after weeks of cold, harsh winter, the sun is bright and the temperature is 72 F.  Upland Chorus Frogs are calling from the wetlands, gnats swarm in circles in the meadows, and…large masses of fire ants bask in the sun.  Displaying  an unusual and little studied behavior, entire colonies of the Red Imported Fire Ant (Solenopsis invicta) leave their underground chambers to lie in tangled masses in the warm sun.

The following photographs were taken during an identical occurrence in January 2010.

Masses of Red Imported Fire Ants -  Solenopsis invicta

Masses of Red Imported Fire Ants –
Solenopsis invicta

Masses of Red Imported Fire Ants -  Solenopsis invicta

Masses of Red Imported Fire Ants –
Solenopsis invicta

Red Imported Fire Ants Solenopsis invicta

Red Imported Fire Ants
Solenopsis invicta

Fire ants are highly temperature sensitive.  Because they are incapable of surviving long, cold winters, their range is limited.  In North Carolina, they have not spread into the northern border counties or most of the mountains.  In Virginia, they inhabit only a few southern coastal counties.

Thermoregulation is an important biological imperative for fire ants, as demonstrated by their willingness to completely expose most of the colony during sudden, short warm spells in the wintertime.  One or two days of warm weather in mid winter is not enough to warm the soil at the surface of the mound, so the only way for the ants to warm themselves is to come outside the mound into the sun.  Even queen ants have been reported on the outside surface during these basking episodes.  This would appear to be a risk to the colony, but apparently the benefit of warming outweighs the risks.

Herb Amyx

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2 Responses to Fire Ants Catch a Little Sun

  1. stone says:

    In my garden, they seem to do this only when hauling out the dead winter-kill. Those dead ants linger on top of the burrow for weeks, while the rest of the colony continues business as usual.

    • Interesting observation. There are several references speculating that the ants use these short warm periods to clean debris out of the burrows in addition to basking, so it would be logical that they would move dead workers out as well. Thanks for your comment.

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