NC State researcher is fascinated by aromas of ants

N.C. State researcher Clint Penick, center, studies ants in the field.
N.C. State researcher Clint Penick, center, studies ants in the field.

Ants have strong odors. Crush one and you’ll detect notes of citrus, vinegar, chocolate, or any multitude of other aromas – depending on the species.

That’s something most people probably never have realized, but scientists have known it, and for over a half a century most of them have described one in particular – the odorous house ant – as reeking of rotten coconut.

It’s a description that never settled well with ant biologist Clint Penick, though. In fact, he thought it stank.

“It smelled like blue cheese to me,” said Penick a postdoctoral researcher at N.C. State, recalling his first whiff of crushed ant when he moved to North Carolina, where the little bugs are prevalent. “I didn’t get any coconut.”

Yet, only two of the 100 insect-themed websites Penick researched described the odorous house ant as reeking of blue cheese. Rotten coconut always took top billing.

Like any research scientist would, Penick decided to figure out why.

To understand why it’s so important to differentiate between two pungent odors, it’s helpful to understand why scent is so important to social insects like the ant in the first place.

Ants communicate mainly through scent, and for a variety of reasons, mostly to signal danger to their colleagues.

“If you crush an ant, that tells all of her nearby sisters that they are under attack and they should either run away or help her,” said Penick.

Research also shows that the chemical responsible for an ant’s scent also aids in helping to keep its body clean, per some kind of anti-microbial component. Although that’s a less explored theory in ant biology to date, it could lead to new antibiotics for humans one day, said Penick.

But that’s down the road a bit. For the present, knowing how to identify insects by scent helps homeowners determine which kind they have so they can eradicate them when they become prevalent pests.

The odorous house ant is one of the most common pests in North Carolina and other eastern states, but what is it that makes them stink, and how many people really know what rotten coconut even smells like anyway?

The first question Penick answered in his lab, where he discovered that ants contain methyl ketones, the same compound responsible for blue cheese’s pungent odor. Fresh coconut did not. But the coconut he buried in his backyard – the one covered in thick blue-green mold when he dug it back up – did contain the same methyl ketones.

“It turns out the mold that was on it is the same type of mold that’s used to make blue cheese,” he said. “So in a twist, rotten coconut actually smells like blue cheese.”

Penick was willing to bet that when given the choice, most laypeople would describe the ant’s aroma as blue cheese, not the more obscure rotten coconut.

To prove it, he set up a booth at BugFest last September; that’s the annual event at Raleigh’s N.C. Museum of Natural Sciences that educates the public about insects of all kinds. Passersby were invited to take a whiff of crushed odorous house ant, then describe the aroma by choosing either rancid butter, blue cheese, rotten coconut, or a write-in answer.

“The blue cheese was the favorite when we went to the people,” said Penick.

It was enough for him to take his results to those websites, requesting they change the ant’s aroma description from rotten coconut to blue cheese.

“The project started out as kind of a joke to figure out what ants smelled like, but in some ways we actually uncovered what I think was actually a very important problem,” said Penick. “There’s a hundred websites that were telling homeowners how to identify a particular species in their house, and it was wrong.”

The sniff test

When crushed…

  • carpenter ants smell like vinegar.
  • citronella ants smell like lemons.
  • trap-jaw ants smell like chocolate.
  • odorous house ant smells like blue cheese.