A Staff Report from the Straight Dope Science Advisory Board

What accounts for the smell of crushed ants?

May 9, 2006

Dear Straight Dope:

Ever since I was a young boy, I have fought a battle against swarms of ants that invade the kitchen counter every summer. I have always noticed that when smashed, usually in large numbers, the ants smell somewhat like lemons and soap, yet more pungent. What does this smell come from?

What you're getting a whiff of when you crush an ant are just a few of the more volatile components of the potpourri of chemicals ants produce. The body of an ant (depending on genus and species) has, on average, around ten glands producing different chemicals, serving a variety of functions including defense, communication, alarm, trail-marking, and antibacterial and antifungal purposes. The communication and alarm chemicals are generally the ones humans smell because they need to be volatile in order to work, and the alarm compounds are going to predominate when you're crushing and killing them. In most cases, the ants voluntarily release the alarm chemicals, but some alarm chemicals can only be released when the ant is being killed. Either way, these compounds, singly or in combination, warn nearby ants of trouble. Ants near the spot where another ant is killed suddenly become hyperactive and alert--some species fall into a blind panic, while others become aggressive to the point of suicide. That's all triggered by some of those chemicals you smell, one of the more common ones being citronellal, a lemony-smelling compound related to what's in citronella candles.

Of course, when you crush an ant, you're releasing a lot of other glandular products that aren't part of the alarm system. Some of the most interesting are found in the metapleural gland (present in almost all ants), which often includes phenols or phenylacetic acid. These are potent antiseptics with dramatic antibacterial and antifungal properties. Ants, after all, typically live in the soil, where they're constantly exposed to dangerous microbes, and ant nests are fantastic places for fungi to grow--or rather they would be fantastic except for the chemicals ants have all over their bodies, often permeating the nest and everything in it, which help keep things sterile. Ants almost never get sick. In answer to a recent question about whether it was safe to eat a cookie that ants had been crawling on, I explained that the cookie was probably cleaner after the ants had touched it as a result of their metapleural gland secretions. It's as though human sweat contained Lysol. If we were as chemical-covered and germ-free as the average ant, we'd all live longer, healthier lives. That smell coming off those crushed ants is not just the smell of fear and death, but also the smell of true cleanliness and health.

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