A visitor prepares to sniff the odorous house ant. Photo credit: Magdalena Sorger.

A visitor prepares to sniff the odorous house ant. Photo credit: Magdalena Sorger.

This past weekend at the North Carolina Museum of Natural Sciences annual BugFest, we convinced a couple hundred people to sniff ants. We started off light, with a bouquet of lemon and citrus from the citronella ant, Lasius claviger. Then we plowed ahead, shoving an angry carpenter ant under the nose of anyone who would take it to demonstrate the acrid, vinegar smell of formic acid. If the participant was still with us, we moved onto our main quarry: the odorous house ant.

First, I have to admit that through this entire exercise I had an ulterior motive. The odorous house ant is unquestionably odorous, but there is debate about what exactly that odor is. OK, maybe “the debate” is more of a personal grudge, and maybe I spend a little too much of my free time smelling ants, but please bear with me on this.

The odorous house ant is one of the most common ants in North America. It belongs to a group of ants famous for smelling like blue cheese. Again, “famous” might not be the right word here, but most species in this group do smell amazingly similar to blue cheese. This is where the controversy begins. Online, numerous websites purport that the odorous house ant is the exception to the rule. Instead of blue cheese, these sites claim that the odor is…rotten coconut!

Now, I don’t have a problem with ants smelling like coconut. In fact, I really wanted the odorous house ant to smell like coconut. After moving to Raleigh from the west coast, where the odorous house ant is rare, I was looking forward to my chance to smell the “coconut ant.” So when spring finally came and a colony of odorous house ants emerged in my yard, I grabbed a couple workers and held them to my nose. What happened? Nothing. I mean they smelled, but they smelled like any other blue cheese ant. There was no coconut, rotten or otherwise, and certainly no, “Sickening-sweet smell, like a coconut piña colada,” that I read on one website.

Not unlike rotten coconut itself, the experience left a bitter taste in my mouth. So I turned to the internet and found that over 80% of the sites mentioning the odorous house ant also described some “coconut-like” smell (Fig. 1A). Only two sites out of a hundred mentioned blue cheese! Could my nose be that wrong? I doubted it, so I went to the people. This is how the unsuspecting participants of BugFest got roped into my crusade to identify the smell of the odorous house ant.

 

The percent of websites (A) or respondents (B) that identified each smell as that of the odorous house ant.

The percent of websites (A) or respondents (B) that identified each smell as that of the odorous house ant.

At our display table, we gave the participants four choices: A) rotten coconut, B) blue cheese, C) rancid butter, or D) other, which allowed a write-in candidate. I did my best to remain non-biased, but in the end I was vindicated when blue cheese won by a slim margin (Fig. 1B). Rotten coconut got a fair number of votes also, but “other” came in second place. Topping the list for write-in candidates: “cleaning spray” and “paint,” and one little girl said the ants smelled exactly like her doctor.

So what is the real answer? We don’t know yet, but we’re not stopping there. In collaboration with Adrian Smith at the University of Illinois, who is working on the trail pheromone of odorous house ants, we’re conducting a chemical analysis. We’ll sample the compounds released by blue cheese, rancid butter, rotten coconut, and of course the ants. Maybe we’ll even try to find that little girl’s doctor! Who knows? When the results are in, we’ll write up our assessment and share the results with the world. Until then, we’ll be trying to figure out how, exactly, to rot a coconut. Any ideas?

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