Surprise! Some Ants Smell Like Chocolate

Gleefully crushing ants in the manner of a child menace isn’t exactly a good look for any self-respecting adult. But doing so in the name of science is another matter—and it’s revealed some fascinating olfactory intel.

When you squash a trap-jaw ant (genus Odontomachus), it releases a pheromone from its head that warns other ants of the nearby threat. To us, the pheromone smells like chocolate. “I've done it only once to see if it was true but normally try to avoid it,” Clint Penick, a Kennesaw State University assistant professor of ecology, evolution, and organismal biology, told Live Science.

It wasn’t Penick’s only foray into the world of ant aroma. In 2015, he and a colleague, Adrian A. Smith, published a study in American Entomologist that helped answer an age-old question among insect sniffers: What do odorous house ants (Tapinoma sessile) actually smell like?

They began their research by compiling a list of the most common responses on the internet: rotten coconut, rancid butter, and blue cheese. They then asked 143 attendees of North Carolina’s 2013 BugFest to each squash a house ant and choose which of those three options best matched its odor. They could also write in their own response, and “cleaning spray” proved most popular there (though one young girl reported that the dead creature smelled like her doctor).

While rotten coconut was cited most often online, blue cheese came out on top in the in-person survey. Penick and Smith then analyzed the chemical compounds responsible for the scents of the two substances—plus fresh coconut—and compared them to those of house ants. The rotten coconut, blue cheese, and odorous house ants all contained methyl ketones. The fresh coconut didn’t, leading the researchers to conclude that “it is not the ‘coconut’ in rotten coconut that smells like the odorous house ant, but the ‘rotten.’”

Other types of ants have unique odors, too, which can help them deter predators. Yellow ants give off a lemony citronella scent; and carpenter ants and wood ants emit formic acid, which smells like vinegar.

[h/t Live Science]