Ant Bigheadedness Makes for Powerful Army

Colonies of big-headed ants, one of the world's worst invasive species, produce larger soldiers with these giant noggins when up against other ant species that know how to fight back, a new study describes.

Pheidole megacephala are found in more than 1,600 sites across the globe, bad news for any native ants, spiders, beetles and other invertebrates that aren't prepared for their aggressive brand of warfare.

"If you think about the worst invasive species, ants frequently show up on those lists, and big-headed ants are among the most problematic," lead auhor Andrew Suarez said in a statement. "They are very aggressive. And unlike a lot of native ants, they produce large numbers of queens, so they have incredibly high potential for reproduction."

Big-headed ants spread out, assembling multiple nests that cooperate on defense, reproduction, territorial expansion and food procurement, according to researchers. And their disproportionately large heads don't mean that these ants have big egos. Rather, their heads are used to give their mandibles a powerful bite, which they use to attack other ants and cut up prey.

So how exactly do Pheidole ants get such big heads? It turns out that it's all in their diet. Changes in nutrition during development, which effect hormone levels, are primarily responsible for their different shapes and sizes.

Researchers wanted to know if environmental cues, such as the presence of other aggressive ants, would cause the big-headed ant colonies to produce more, or bigger, soldiers. Described in the Biological Journal of the Linnean Society, the research team looked at ants in Australia, Florida, Hawaii, Mauritius (an island off Africa) and South Africa.

According to the study, big-headed soldiers grew three times more massive than those in Hawaii, and were intermediate in size at the other study sites.

"This shows that they were able to adapt to a new environment relatively quickly," Suarez said. "It's kind of exciting and scary that it can happen so quickly."