They reminded scientists of dragons so much, they named them after two of the fire-breathing beasts from the Game of Thrones.
The two new ant species from Papua New Guinea, named Pheidole drogon and Pheidole viserion, have spiny barbs along their backs and shoulders with an unusual set of muscles beneath them.
Researchers previously thought that barbed spines evolved as a defense against predators. But discovering muscles both in and under the spines of the dragon-ants has led researchers to propose they may also help the insects hold up their often over-sized heads.
The team began their discovery by hunting for specimens of spiny Pheidole ants with exaggerated shoulder and back spines in museum collections across the USA and Japan. Then, with a technique called microtomography, which is similar to a hospital CT scan, they peered through the exoskeleton and into the bodies of ants from different social ranks.
Most of the populations of Pheidole ants have ruling queens, small but busy “minor” workers, and brawny “major” workers, also called soldiers. The majors have large heads with massive mandibles that act as biological milling stones, crushing seeds too hard for minors to crack open. The major’s oversized heads are already packed with muscles to help them lift these heavy objects.
In research published in PLOS One, lead author Eli Sarnat at the Okinawa Institute of Science and Technology suggests the newly uncovered presence of muscles could indicate the spines might also play a role in holding up their gargantuan heads.
Study shows that deserts ants can walk and navigate backwards when moving oversized food, a discovery that could inform robotics, researchers say
“In all likelihood, the spines serve as a kind of defensive mechanism, but one problem is how they evolved in the first place. A little spine won’t help as a defence mechanism. So there could have been another use that would have given them an advantage when they were little,” said Sarnat. “The spines in the back do not have any muscles like the shoulders, so [shoulder] spines might be important as a skeleto-muscular support mechanism for the head in soldiers.”
“It’s intriguing that these ants have such amazing spines, and interesting to consider that they may serve a function other than as a defense,” said James Traniello of Boston University, who was not involved in the study.
But he said more experiments were needed to test the theory, because while minor workers have smaller heads than the majors, they still have barbed spines. “Spines actually seem to be equally well developed in minors and majors, so that needs to be considered,” said Traniello.
Sarnat agrees that more remains to be understood about how the spines and muscles evolved, and said his team has plans to study their function further.
As for the namesake inspiration, Sarnat confesses not everyone was completely satisfied with the Game of Thrones choice. “Originally I had asked my wife for help, and she came up with something meaning split-horns, which was really good - a classic name for ants,” Sarnat said. But the other scientists realised the jet-black colour of P. drogon and cream of P. viserion matched the dragon scales from the fantasy drama, which they were all fans of.
“We thought it would be a little more fun, but my wife wasn’t too pleased,” Sarnat said. “She’ll get to name the next one.”