Brazilian Ants Sacrifice a Few Relatives Each Day for the Greater Good

By Eliza Strickland | September 29, 2008 1:03 pm

antsIn a striking example of the evolutionary benefits of altruism, researchers have found a species of ants that sends a few workers out each evening on a suicide mission to ensure the continued survival of the colony. The tiny ant Forelius pusillus, which makes its home in sugar cane fields in Brazil, makes a nightly ritual of covering the entrance to its nest with sand. To be sure that the entrance is sealed shut tightly, a few ants remain outside each evening to finish kicking sand over the hole. Those ants, stuck outside in the cold and the wind, die during the night.

“In a colony with many thousands of workers, losing a few workers each evening to improve nest defense would be favored by natural selection,” said co-author Francis Ratnieks…. The ants stuck outside might be old or sick, [co-author Adam] Tofilski conjectured. Thus, they may have essentially sacrificed themselves for the greater good, being more expendable members of the colony [ScienceNOW Daily News].

The new study, which will be published in the November issue of The American Naturalist [subscription required], adds a new twist to the phenomenon of altruism and self-sacrifice among insects. There are many examples in nature of insects sacrificing themselves when a colony or nest is under attack, such as when bees use their stings to defend the hive and die in the process. But the door-sealing activities of these 2-millimetre ants … represent the first recorded case of insects sacrificing themselves through a premeditated and pre-emptive procedure [New Scientist].

It remains a puzzle what the ants are guarding their colonies against. [One entomologist] speculated that F. pusillus might be hiding from large, roaming colonies of army ants [ScienceNOW Daily News].

Delve deeper into the puzzle posed by cooperative insects in the DISCOVER interview with the scientist who first promoted the ideas of “kin selection” and “group selection,” E. O. Wilson.

Image: Wikimedia Commons

MORE ABOUT: altruism, evolution, insects
  • Alex

    It’d be nice if you didn’t illustrate your article on the Brazilian species Forelius pusillus with a photo of the European species Camponotus cruenatus. That’s kind of like showing a picture of a squirrel when your article is about monkeys.

  • Eliza Strickland

    I couldn’t find a free, readily available image of Forelius pusillus! And believe me, I tried. But here in the blogosphere, we don’t always have the luxury of spending an hour tracking down a researcher who can provide a photograph. I figured only a few people would know the difference– clearly you, sir, are one of those few.

  • Opondo

    This is significant if indeed the research findings are correct. I wonder how Dawkins would explain these findings.

  • Alexander (the one who does not know the difference

    Thank you. Thank you for the article Ms. Strickland. Just wonderful. And thank you too, Alex for sharing your knowledge with us. Really impressive. I wish we can inlude more of something like that in elementary education. I wish we have more news like this on TV.

  • Otis

    Well Alexander, this should please you.
    I am a current 9th grader doing a report on this exact article and will be sharing it with my class.
    So in some way it is getting into the educational system.

  • Cody

    Well Alexander, your wish is coming true.
    I am a current 9th grader doing a report on this exact article and will be presenting the information to my entire class.
    So in some way the news is making its way into the educatioal system.

  • MB

    Who send these worker out on duty?
    We already know that ants are the most organised society on the planet and that has been going on and known for abou 8 million years. but still no academia have explained how the ants society function with regard to communication , hierarchy, law and order.
    There are strict orders ants and bees follow without failure, who is behind these laws that govern these great species.
    Human has their laws for example the ten commandements, hardly used
    we are an extinct society and we wont’ live longer than the ants and bees they are already older than we and will continue to live way beyond our extinction.


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