Why fire ant rafts are floating in Hurricane Harvey floodwaters but did not appear after Katrina

Dramatic images of rafts of fire ants floating around in flood waters have been shared across social media in the aftermath of Hurricane Harvey.

People have been warned not to touch the rafts seen around Houston, Texas, because of the risk of the angered ants stinging en masse.

But the presence of the rafts prompted people to think back to Hurricane Katrina which caused deadly destruction 12 years ago in the neighbouring state of Louisiana.

Where were the fire ants then?

The creatures were just as prevalent in the state as they were in Texas before the respective Hurricanes but the same pictures of water resistant ant colonies floating to find dry line were not recorded.

Professor Craig Tovey from Georgia Institute of Technology, who has conducted research around fire ants, their rafts, and how they react in water was scratching his head.

He said: “When I started seeing the photos (from Houston) I thought we just didn’t see that with Katrina.

“They are present in both locations. It’s not that there aren’t any fire ants in New Orleans.”

The difference was the speed in which the water engulfed the two cities.

“In New Orleans there was a storm surge, the levees broke, the water was very rapid.

“In Houston all the flooding came from hours and hours of rain.”

Fire ants have been spotted in flood waters around Houston following Hurricane Harvey
(Georgia Institute of Technology)

It was similar to when Tovey and his colleagues first tried to catch fire ants for their research, albeit on a different scale.

Initially they bravely poured water in to fire ants to trigger an evacuation hoping to catch the ants but only succeeded in drowning the insects.

What they learned was that to initiate an exodus the water needed to trickle in.

Fire ants have been spotted in flood waters around Houston following Hurricane Harvey
(Georgia Institute of Technology)

In New Orleans, the fire ants drowned from the mass onslaught of water before they even had a chance to show off their scary raft building schemes. Whereas they had the perfect conditions to get organised in Texas.

Tovey added: “The ants had 24/36 hours to gradually emerge in Houston.”

Fire ants originated from South America but have been in the US since at least 1918 and are considered a major pest.

Their raft-building skills were honed in the natural habitat on the banks of the Amazon.


 

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