Mammals Have Evolved Into Ant Eaters 12 Times Since The Dinosaurs Went Extinct

Social insects like ants and termites are a substantial component of the land’s biomass, which explains why so many different species of animal like to munch on them. Today, there are over 200 mammal species that are known to eat ants and termites, but only 20 of them are obligate eaters – like anteaters, aardvarks, and pangolins – which have evolved specialist anatomy to consume them as their sole food source.

But when did this specialization first evolve across these various species? For a long time, scientists were not clear on this point, but recent research has shown that this adaptation has occurred 12 times since the Cenozoic era, which was around 66 million years ago.

This type of convergent evolution among mammals towards this dietary specialism – known as myrmecophagy – first emerged following the K-Pg extinction. This large-scale extinction event killed the non-avian dinosaurs and drastically transformed the ecosystem. In doing so, it set the stage for ants and termite colonies to quickly expand across the world, driving the need for some species to adapt to eat them.

“There’s not been an investigation into how this dramatic diet evolved across all known mammal species until now,” Philip Barden, associate professor of biology at New Jersey Institute of Technology, explained in a statement.

“This work gives us the first real roadmap, and what really stands out is just how powerful a selective force ants and termites have been over the last 50 million years – shaping environments and literally changing the face of entire species.”

To understand this evolutionary story, Barden and colleagues compiled dietary data for 4,099 mammal species using nearly a century of natural history records, as well as conservation reports, taxonomic descriptions, and dietary datasets. 

Species were sorted into five dietary groups that ranged from strict anti- and termite-eaters (obligate), to generalists like insectivores, carnivores, omnivores, and herbivores. These categories were determined by published data on the animal’s guts and field observations.

“Compiling dietary data for nearly every living mammal was daunting, but it really illuminates the sheer diversity of diets and ecologies in the mammalian world,” Thomas Vida, from the University of Bonn, added.

“We see fruit-eating foxes, krill-eating seals and sap-drinking primates, but few rely exclusively on ants and termites … the ecomorphological adaptations required are such a major barrier. One thing myrmecophages share is an almost insatiable appetite – ants and termites are so low in energy that even a small animal like the numbat must eat about 20,000 termites a day, while an aardwolf can hunt up to 300,000 in a single night.”

In addition to focusing on the anteaters, the team also traced ant and termite colony sizes across time, going as far back to the Cretaceous period, around 145 million years ago. This helped them to understand when the insects became a reliable food source.

At that time, ants and termites were very few in number compared to today. They accounted for less than 1 percent of insects on Earth. This is tiny compared to 15,000 species inhabiting the world today, which accounts for a combined biomass that exceeds all living wild mammals. These insects did not reach this modern level until the Miocene, around 23 million years ago, when they crawled their way to being around 35 percent of all inspect specimens.

“It’s not clear exactly why ants and termites both took off around the same time. Some work has implicated the rise of flowering plants, along with some of the planet’s warmest temperatures during the Paleocene-Eocene Thermal Maximum about 55 million years ago,” Barden added.

“What is clear is that their sheer biomass set off a cascade of evolutionary responses across plants and animals. While some species evolved defenses to avoid these insects, others took the opposite approach – if you can’t beat them, eat them.”

The analysis revealed that myrmecophagy evolved at least once in each major mammal group (placentals, monotremes, and marsupials). But this evolution was uneven, suggesting that some lineages were more “predisposed” to ant and termite eating.

At the same time, all the myrmecophages came from insectivore or carnivore ancestors, with the former making the transition three times more often than the latter. But within the carnivores, some families (including that of dogs, bears, and weasels) account for about a quarter of all origins.

“That was a surprise. Making the leap from eating other vertebrates to consuming thousands of tiny insects daily is a major shift,” Barden explained. “Part of the predisposition may lie in certain physiological features or dentition that are more malleable for handling a social insect diet.”

Interestingly, the team found few examples of myrmecophagous mammals switching back to more conventional diets or further diversifying after they’ve made the evolutionary leap. The only exception here is the elephant shrew, which became an omnivore after becoming one of the first myrmecophages in the Eocene – hoppy little hipsters.

This ability to embrace myrmecophagy and to never look back may have helped these different species in the past, but it could put them at risk in the long run, resulting in an evolutionary dead end.

“In some ways, specializing on ants and termites paints a species into a corner,” Barden said. “But as long as social insects dominate the world’s biomass, these mammals may have an edge – especially as climate change seems to favor species with massive colonies, like fire ants and other invasive social insects.”

The paper is published in Evolution.