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How Ants, Once Blind, Evolved to See Again

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About 80 million years ago, several kinds of tropical army ants went underground. Like many predominantly subterranean species, they lost their sight. They also lost the parts of the brain associated with sight.

Eighteen million years ago, a few species of army ant—Eciton hamatum, Eciton mexicanum and Eciton burchellii—resurfaced. Researchers from Drexel University have found evidence that they regained their sight, and regrew parts of the brain associated with sight. The research is published in the journal The Science of Nature.


Testing an ant’s sight is a tough proposition, so the researchers aren’t able to measure exactly how good the newly-sighted ants’ vision is. But there is evidence that the ants’ ability to see isn’t just a simple recovery of their original visual system.


“We found anatomical suggestions that their eye structure is distinct from most other above-ground insects,”said Sean O’Donnell a professor at Drexel and one of the paper’s authors. “The ants may have both regained lost ground and reinvented the mechanisms required for sight.”

The change in the brain was even more remarkable than the change in the eyes. The resighted species had significantly larger optical lobes than their subterranean relatives. The above-ground ants also had expanded the regions of their brain that dealt with smell, and had larger mushroom body calyces, which are associated with memory.

In addition to saying something about our abilities, this also says something about our environment. Living above ground, with day and night, and a wider variety of both prey and predators, apparently requires more brain power than living below ground. The possibility of regaining brain is exciting enough. According to O’Donnell, “Our data on visual investment suggest there is at least some room to regain or increase lost sensory and cognitive function.”

[The Science of Nature, Drexel University]