Illustration: Anders Svernsjö.
Nicholas Aflitto knows how this is. He is a PhD student at Cornell University in the US and is doing research on how animals behave and are affected by sound. His research is focused on how animals behave and are affected by sound.
He has been interested in the subject ever since he as a child started learning music. The gateway to the interest was when he as a 9-year-old made his first experiments and became fascinated by how different music styles can influence one's mood. Today Nicholas has broadened his research to include how animals communicate with each other by chemical means, such as volatile substances that are emitted from organisms. Nicholas Aflitto
Sound is animal language
We humans communicate through our language, which consists of composite sounds. But we can also communicate in other ways, such as body language. We also get impressions through taste and smell.
Animals also use sounds to communicate. Other signals than sounds are important for animals' communication as well. They are influenced by everything from visual signals to smell. The animals must quickly decide how to respond to these signals in order to survive.
Each time Nicholas is studying an animal, he feels that he tries to learn its language.
- I have for example managed to ward off tree-killing bark beetles from entering logs using the sound they emit when they are hunted by predators. It is a biologically-relevant sound that is important for bark beetles. If I had tried sounds that are not biologically relevant for bark beetles, it would not have worked out so well. Sounds that are not biologically relevant don't mean anything to bark beetles, Nicholas Aflitto says (picture).
Sonic pest devices don't speak the languages of mice and other animals
There are many commercial sonic pest devices that you can buy. They are said to scare away everything from mice and rats to insects. Many of them make use of ultrasound, which is sound with frequency above 20,000 Hertz. Such sounds can't be perceived by humans.
- I have not seen any sonic pest devices which manage to scare off pests with the use of non-biologically relevant sounds. Scientific studies have not shown any effect of the commercially available devices, Nicholas says.
Ultrasound doesn't help against insects either
Ultrasound does not drive away mosquitoes, lice and spiders. Mosquitoes also communicate at lower sound frequencies than ultrasound.
- Even with insects, biologically-relevant sounds are required to provoke a lasting response, Nicholas says.
Sound has proved to be attractive to insects such as mosquitoes. One example is that traps that mimic the sound of female wing beats can attract male mosquitos. The sound is species-specific, so the wing sound of a certain species of mosquitos will only attract mosquitos of the same type, not of other species.
Animals get used to sonic pest devices
With time mice and rats tend to respond less to new sounds. It could be a potential danger, but when nothing happens, they get used to it after a while.
- Animals ignore sounds that don't present a threat. Such sounds are simply not important to them. The explanation for this is that an animal that is afraid of all sounds in its environment will not survive very long. Habituation is not something that occurs only among mammals. I have noticed a similar response working with insects, where a constant sound treatment is eventually disregarded, Nicholas says.
If you want to reduce habituation of sounds, you can't use the sound all the time, you need to randomize it. The best way is also to use biologically-relevant sounds, i.e. to use sounds that are important for that particular animal.
Actually, perhaps it should not have been so surprising that sonic pest devices don't work. Nicholas again.
- The non-biologically relevant sounds from sonic pest devices are essentially no different from other mechanical sounds such as sounds from a home heating system. The animals quickly learn that the heating system is not going to harm them and continue with what they are doing, as if the sound was nonexistent.
Why are sonic pest devices sold if they don't work?
In the 60's it was believed by some that ultrasound could serve to scare away pests, but later research has not provided any support for this. There is also a large interest to use easy and environmentally-friendly pest control solutions.
Mice and other small rodents have a much wider hearing range than humans. Their hearing abilities extend well into the ultrasonic range. They hear ultrasound unlike humans, which could be an explanation why the industry has focused on developing sonic pest repellents that emit ultrasound. Something that scares pests, but doesn't bother you as a person, is of course a great selling point. The fact that it doesn't work, is another matter. But what everybody might not realize is that pets like cats and dogs, can hear ultrasound.
Customized pest devices might work
Nicholas thinks you can change the behavior of mice and rats with sound. If one is to construct a customized sonic pest device that works, a good starting point might be to use the sound of a frightened mouse or a mouse that has been injured. The sound of a mouse being pursued by a predator represents important information for other mice.
The sonic pest devices that use non biologically-relevant sounds are not effective. As technology becomes more affordable and researchers continue to learn more about how organisms process acoustic signals, novel sonic devices will become available. Then you could combine biologically-relevant sounds with visual cues and smell. Future pest devices would then not only be able to sound dangerous, but also look and smell scary.
Nicholas hopes that his research will ultimately highlight the importance of sound in many organisms and uncover novel pest control tools that will reduce environmental damage without the use of conventional methods. We at the Swedish Homeowners Association keep our fingers crossed that he succeeds.
Article in Swedish: Ljudskrämmor jagar inte bort möss och andra skadedjur