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Red imported fire ants are no match for the tawny crazy ant

When red imported fire ants invade an area, they typically displace native ants and threaten unsuspecting people who venture too close to the mound. However, as one study in Science magazine concludes, fire ants have one adversary that they can’t seem to beat—the tawny crazy ant, a species that has a secret weapon against the fire ant toxin.

Specialists have noted that tawny crazy ants outcompete fire ants for resources, including food and shelter. Crazy ants are sometimes discovered living in former fire ant nests, some of which are still partially occupied by fire ants.

While most ant species avoid imported fire ants, whose venom is a potent insecticide, crazy ants deliberately surround and attack them. When scientists observed crazy ant behavior after contact with the fire ant venom, they discovered that crazy ants do a kind of “detoxification” dance, standing on their hind legs, excreting a substance from their abdomen and spreading it on their bodies. Analysis of the substance revealed that formic acid was the main ingredient.

Scientists performed several experiments to determine whether crazy ants could really detoxify the fire ant venom and whether or not the excreted substance could be used to increase the survival rate of other ant species.

In the first test, scientists enclosed one crazy ant worker in a vial containing two fire ant workers. The researchers brushed nail polish on the tail of the abdomen of some of the crazy ants, sealing the opening for the venom glands; in others they brushed the side so the ants could use their glands to produce the substance.

When one of the fire ants touched the crazy ant with its stinger, scientists would remove the fire ants and observe the crazy ant. Death rate was much higher for crazy ants whose abdomen had been sealed (48%) than for those that could still use the formic acid from their abdomen after being exposed to the fire ant toxin (2%).

Scientists also used the formic acid on Argentine ants that had been exposed to fire ant toxin to see if the substance would protect other species as well. When scientists compared Argentine ants covered with formic acid after being touched by the fire ant stinger with Argentine ants covered with a different substance, the ants covered with formic acid had a much better survival rate.

When scientists observed crazy ant behavior with other ant species, crazy ants still did the detoxification dance after being attacked, but not in as high of a frequency as they did after being attacked by fire ants.

Although the researchers did not know why formic acid protects crazy ants from the insecticidal properties of the fire ant venom, they said that the acid and use of it may be an evolutionary trait, as crazy ants and fire ants have coexisted for centuries in northern Argentina, Paraguay and southern Brazil.

Red imported fire ants were discovered in the U.S. in the 1930s, and the tawny crazy ant was discovered in 2002 by pest control operator Tom Rasberry.

Sources: Milius, S. In crazy vs fire, the ant with the detox dance wins. Science News, 13 Feb 2014. Online at https://www.sciencenews.org/article/crazy-vs-fire-ant-detox-dance-wins

LeBrun, E.G., Jones, N.T., and Gilbert, L.E. Chemical warfare among invaders: A detoxification interaction facilitates an ant invasion. Science. Posted online February 13, 2014. doi: 10.1126/science.1245833

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