It’s an ongoing debate on TikTok: A couple wonders why one of them can smell ladybugs and the other can’t.
Below that video, one commenter notes that ants smell, too, like a “combo of tomato vine and dirt.”
Another commenter says the ant smell is more like “blue cheese or pen ink.”
And one less fortunate commenter notes: “I can smell roaches. It’s the worst superpower I have ever developed.”
Just like “the dress” divided the internet a decade ago, the insect smell question is one of the latest debates.
So, why do some people pick up these odors, while others don’t? The answer goes back to how humans are able to smell in the first place.
Smells travel in the form of molecules, and humans have hundreds of odor receptors that enable us to detect them. “We use them to smell thousands and thousands of odors,” says Claire de March, a biochemist at the French National Centre for Scientific Research in Grenoble. “One odorant molecule will activate a pattern of those odorant receptors.” Those receptors then transmit a signal to the brain, which interprets it as a specific odor.
“One odorant receptor can be activated by multiple types of odorant molecules, and one molecule can activate several types of receptors,” says de March.
But here comes the tricky part: Not every human has the same receptors. “And that can translate in massive difference in perception,” says de March. “If I have a version of a receptor, I will smell an odor in a way, and if you have another version, this odor will smell different to you.”
There are several known examples of this, says de March. For example, the coriander plant—also known as cilantro—has leaves that some people perceive as “soapy,” while for others they smell pleasant.
These discrepancies can also explain how we smell insects. Some people might have odor receptors that allow them to pick up a smell emitted by an insect, while “one person simply may not have a receptor that’s picking up this particular odor,” says Robert Mitchell, an entomologist at Penn State University.
Of all the possible odor receptors a human could have, “any individual human will have most of these, but probably not all of them,” he explains. “The individual may be missing a few receptors, or there may be some duplicates.” What’s more, of all the receptors present, about half will be “broken in some way to make them nonfunctional,” Mitchell says. “DNA mutations within the receptors can change their function. You and I might both have a copy of the same receptor, but they could have different sensitivities.”
For example, in the case of bedbugs, when there are many of them in a house, the odor—often described as a musty, sweet smell like marzipan—becomes perceptible to humans. But people who are less sensitive to smell might not be aware of it as quickly. “I could easily see situations where some people become aware of this smell before other people do in a residence.”
“There’s many different things that could vary between the person that could strongly affect what they can detect and how much of it they could detect,” says Mitchell. “And when you combine this with the sheer number of odors that insects are producing, the sort of natural conclusion is that there’s probably some odors from insects that someone can smell, and other people can’t.”
What kinds of smells do insects produce?
Most insects do smell, and they produce scents for a variety of reasons. One is self-defense, says Jason Dombroskie, an entomologist at Cornell University in New York. For example, stink bugs produce an unpleasant odor to deter predators from approaching.
Another reason insects give off scents is to attract a mate. “Usually, the females will produce a pheromone, and that pheromone will drift into the wind, and then the males are sensitive to certain chemicals in that pheromone,” and will follow that to find the female, says Dombroskie. In some species, a male will also produce a smell to communicate that he’s healthy and in good shape.
Some insect species, such as European firebugs and some ladybugs (aka ladybird beetles), also use smell to know how to meet up. “What the first one will do is it will lay a chemical trail down, and then the next one finds that trail and reinforces that trail to make it stronger,” Dombroskie notes. “And eventually, all of them will come to that one spot in one tight group.”
In general, smell is a fundamental sense for insects to navigate the world around them. “They’re smelling their way through life, not seeing their way through life, like us,” he adds.
Dombroskie says, though, that humans likely can’t pick up on any mating scents—just the self-defense ones. “They’re trying to dissuade us from eating them,” he says.
And while we’re likely to smell the insects’ self-defense odors, there is another scent that could come into play. For example, with roaches, people might not smell the insects themselves, but the byproduct of chemicals, he says. In other words, you might be smelling their poop.
Sometimes, it might also come down to not being able to distinguish between different insect species: When someone says they smell ants, it could be that they are smelling a particular species, like citronella ants, which produce strong odors when bothered, says Dombroskie. But other people might be referring to another ant species that doesn’t produce the same odor, leading to a confusing dilemma. Basically, part of the debate might just be a misunderstanding.
So, can you smell insects? It might be a great topic to discuss over your next dinner with friends. Or, if you’re bringing up bedbugs or roaches, maybe not.