More than 200 species are classified as "army ants" because of their odd and aggressive behavior; they exist primarily as nomads rather than building nests, their queens cannot fly, and they famously attack their prey in an incredible swarm.
But how this behavior became so popular remains a mystery. Some researchers held that the behavior evolved separately on different continents. But in 2003, Cornell University researcher Sean Brady published a paper concluding that "army ant syndrome" evolved exclusively on the supercontinent Gondwana, and spread its ferocity around the world from there.
If true, this hypothesis means that army ants have been terrorizing the world for more than 100 million years.