Lawrence, a newsletter subscriber, recently emailed me this question:
"I have heard that when a person is walking toward a cockroach, it will feel the advancing air from the person's movement and the bug will run away from it. So if a person uses a vacuum cleaner and held it close to the bug it will feel the air moving over it from behind and will run away into the vacuum cleaner. Any truth to this?"
Indeed, there is truth to this. Dr. Hananel Davidowitz of the NEC Research Institute in Princeton, NJ, actually studied the effect of air flow from a vacuum cleaner on cockroaches.
Cockroaches think with their behinds, in a manner of speaking. On their posterior ends, cockroaches have a pair of appendages called cerci. Fine hairs on the cerci detect air movements. Nerve cells connected to the hairs help the cockroach make sense of the information.
The cockroach will always retreat by running in the same direction as the air flow it perceives. Ever try to stomp on a cockroach? It will feel the push of air from your foot as you bring it down, and miraculously escape being crushed by running forward.
So, what happens when you use a vacuum cleaner to trick the cockroach by changing the direction of the air flow? If you point the vacuum nozzle at the cockroach's rear end, it will feel the air coming from the direction of its head. Since it always flees in the direction of the air flow, the cockroach will do an abrupt about face, and head right for the vacuum.
Here's another interesting bit of research on the topic. Cockroaches will run for cover when you flick on a light switch. During the day, they remain hidden in dark cracks and crevices. Scientists at the Alabama Agricultural Experiment Station wanted to see if cockroaches would be so repelled by moving air that they'd actually choose to stay in a well-lit place to avoid it.
The researchers set up an experiment that gave the cockroaches a choice between hiding in a pipe that had still air but lots of light, or a dark pipe that had an air flow similar to that from a home HVAC system. The cockroaches chose the still air without fail, despite the bright conditions.
How might this information help in designing effective baiting systems for cockroaches? The Alabama scientists believe that by placing roach baits strategically, you can use the flow of air from your home heating and air conditioning vents to direct cockroaches toward the traps.