As humans know and suffer, cockroaches like to gather in groups. What we did not know was the ultimate reason for this behavior. Enigma solved: the key lies in the smell emitted by bacteria from the feces of their fellow humans, an aroma that is irresistible to them. So much so that in their absence they tend to become wandering and solitary critters.
Pheromones are chemicals taken up through smell, and insects use them to communicate and find a mate . Cockroaches use so-called “aggregation pheromones” as a signal to group, but entomologists were unaware of the composition of this compound. Now, research published in the Proceedings of the National Academy of Sciences has revealed that the key is fatty acids related to the action of bacteria present in the waste of these pesky animals.
To reach this conclusion, a team of entomologists from North Carolina State University sterilized a group of German or blonde cockroaches (Blattella germanica) and raised them in germ-free boxes, so their feces would be, too. Later, they exposed another group of cockroaches to these “clean” droppings and other germ-rich ones. Between 80 and 100% of the young specimens preferred the latter. According to the researchers, when the droppings were free of microorganisms, the insects disintegrated; if they fed the cockroaches substances that contained the bacteria in their feces, they would reunite.
Subsequent chemical analysis of both types of feces revealed that the germ-free ones lacked many of the fatty acids related to bacteria and that they evaporate from the feces when they are exposed to the air. The conclusion was that these substances were the aggregation pheromones that had not yet been identified . In fact, synthetic versions of these compounds also induced roaches to congregate.
This discovery will help to better understand the behaviors of different types of cockroach , and could open the door to the development of more effective insecticides, baits and traps.
