As Ants Took Over, Mammals Evolved 12 Times to Eat Them

The combined weight of all the planet's ants and termites outpaces that of all living wild mammals. That wasn't the case in the Cretaceous, when they accounted for less than 1% of Earth's insects. As their numbers changed, some mammals reinvented themselves in order to eat them—at least a dozen times, a new study has found. Published in the journal Evolution, the research charts how these dietary specialists—known as obligate myrmecophages, meaning they eat only ants and termites—arose over the past 66 million years ago.

The surge in ant and termite populations after the dinosaurs' demise apparently prompted a number of mammals to develop unusual anatomical traits—think long sticky tongues and fewer or no teeth—to exploit these insects as a food source. Today, only around 20 mammal species—such as anteaters, pangolins, and aardvarks—are genuine myrmecophages, though over 200 species eat ants and termites to some extent. As study co-author Phillip Barden explains in a New Jersey Institute of Technology article, "There's not been an investigation into how this dramatic diet evolved across all known mammal species until now."

To get to their conclusion, researchers did something "daunting," per co-author Thomas Vida: They compiled dietary data "for nearly every living mammal," some 4,099 of them. The mammals were sorted into one of five groups: those true myrmecophages, insectivores, herbivores, carnivores, omnivores, and herbivores. The researchers then "mapped these groups onto a time-calibrated mammal family tree and used statistical models to reconstruct ancestral diets," per Phys.org, to land upon the determination that mammals evolved to be obligate myrmecophages at least 12 distinct times.

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They found that the evolutionary leap happened at least one time in each of the three major mammal groups—monotremes, marsupials, and placentals—with all myrmecophages having ancestors that were insectivores or carnivores. The study notes that once a lineage adopts obligate myrmecophagy, it almost never returns to a broader diet, with the elephant shrew being the lone exception. These specialists seem locked into their chosen niche, which could put them at risk if ant and termite populations falter. However, as global warming "seems to favor species with massive colonies," per Barden, myrmecophages may hold an advantage—at least for now.