Ant face patterns like swirls and stubble might have practical value

National Harbor, Md. — Looking at face patterns in photos of more than 11,000 kinds of ants struck entomologist Clint Penick as a fine pandemic-lockdown project for his students.

From that socially distanced slog came the idea that the texture patterns might offer practical benefits, says Penick, of Auburn University in Alabama. For instance, some soil-dwelling ants with raised, swirling facial ridges — “almost psychedelic,” he says — could be getting extra protection from abrasion. The ridges lie so close together that sand grains can’t fit in between, he reported at the Entomology 2023 meeting in November.

Most ants have a smooth outer surface, or cuticle. But some grow elaborate patterns, such as tiny indentations “like dimples on a golf ball” or netted patterns like “cracks in mud,” says Penick, who started the project while at Kennesaw State University in Georgia. Ant taxonomists use more than 150 terms to describe the different cuticle patterns, with different names for some subtle distinctions. “They drive people like me crazy,” he says.

Mapping face textures onto an evolutionary tree of ant genera suggests that modern ant lineages must have evolved from smooth-faced ancestors, reported Penick and his former grad student John Paul Hellenbrand, now at the City University of New York, in April in Myrmecological News. Since ants first emerged some 160 million to 140 million years ago near the beginning of the Cretaceous Period, various face textures have appeared, disappeared and sometimes reappeared. The multiple origins got the researchers wondering if the patterns could be of use to the insects instead of just random biological happenstance.               

Textures that look the same, however, might not yield the same benefit in different species, cautions evolutionary morphologist Brendon Boudinot of the Smithsonian National Museum of Natural History in Washington, D.C.  

For instance, possibly abrasion-resistant fingerprint-like ridges show up in desert-dwelling, sand-digging Pogonomyrmex ants but also in their neighbors, trap-jaw Odontomachus ants. Yet trap-jaw ants “don’t push their faces through sand,” Boudinot says, so abrasion isn’t much of an issue. However, trap jaws can snap shut with such force that the ants launch into the air fast and far enough to escape danger (SN: 5/15/15). Their curved face stripes, Boudinot speculates, might “diffuse stress or strain when those jaws are cocked.” But these ideas, he notes, need testing.

Penick agrees that confirmation of any possible benefits to cuticle patterns need experiments instead of just picture sorting. He can imagine other potential upsides: Some patterns might bolster structural support, influence biofilm growth or function in ant communication.

One confirmed benefit of the ant facial features, however, is for humans only. Penick recruited textile designer Meredith West Owens of Wilmington, N.C., to turn parts of ant face images into multicolored fabrics. Pulling small sections from face photos, she colored, stacked and blended each motif into a seamless flow. The effect took “a lot of math,” she says. Her decorative ant-inspired pillows plus a face T-shirt, now sold online, will raise a little money for Penick’s lab.