Many animals make and secrete pheromones in order to control social behaviors, the most well understood of which is mating. In fact, you may have (wrongfully) blamed pheromones for that bad date that you went on last month.
Pheromones are the artificial heart of a huge industry that packages and sells products oozing with the false hope of attracting more sexual partners. There are dozens of perfumes, oils, soaps and even patches on the market, each with the promise of increasing sexual desirability with a spray behind the ears. Although none of these products will bring the results that they promise, because there is no scientific evidence behind any of them, pheromones may be useful to humans in a very different way, but it's far from sexy – improving our ability to trap rats.
In a new study, the Gries group at Simon Fraser University in Burnaby, British Columbia, Canada has made the traditional rat trap 10 times more effective by adding a mixture of pheromones to the trap.
The idea that led to this approach was the long standing observation that traps that had previously caught a rat seem to be better at catching future rats, suggesting that something leftover from the first rat was acting as an attractant for the second rat. Further, the group had previously shown that adding soiled bedding to a trap makes it more effective. This is not surprising, since it is known that rat urine contains chemical signals that communicate with other rats. However, they wanted to take it one step further. In order to build a better rat trap, the scientists first had to identify which specific pheromones would act as the best attractants.
Since volatile chemicals are far more likely to diffuse into the air from the urine —increasing the distance from which rats could sense them — these were a logical choice, as were sex pheromones that were secreted by sexually mature adult male rats.
The details of the test are about what you'd expect. Thirty-two pairs of traps were placed alongside walls of buildings. Each pair consisted of one trap with only food, and the other trap with food plus the mixture of pheromones. The traps were checked weekly and, the results were dramatic. The traps with the added pheromones captured 10 times more rats than the traps with food alone.
This is a particularly exciting finding for those of us living in urban areas. Although New York City maintains that there is no reliable way to estimate the number of rats, and lore puts the number at 8.5 million (one rat per person), a recent statistical study used a reliable method to estimate the NYC rat population at roughly two million. No matter how you slice it, there's a huge rat problem (huge rats, too), as well as in other urban areas around the world. This is attributed, in large part, to the fact that rats are really good at doing one thing — making more rats. So, by doing a bit of biological jujitsu, essentially using the opponent's force against themselves, this group has developed a new method of trickery that may help all of us, from city dwellers to farmers.
In Part 2 of this two-part series, we will investigate the reasons why we cannot use pheromones on each other, as advertised, like we can on rats. Spoiler alert: one big difference between us and rats is that there is no scientific evidence to date that suggests that humans make, or respond to, pheromones.