A green caterpillar with a black head and black spots along its body. The tip of the tail is yellowy orange

These sounds scare humans: Did they come from aliens?

What’s that sound? The aliens are coming! No, wait – it’s only insect defence signals.

These eerie sounds are the result of simulations created by entomologist Jean-Luc Boevé, of the Royal Belgian Institute of Natural Sciences, and informatics engineer Rudi Gio.

They mapped the chemical defence signals produced by sawfly (Craesus septentrionalis) larvae to musical notes, creating a startlingly alien sound.

Insect defence chemicals converted to audio

Boevé first conceived the idea to convert insect chemicals into audio when transforming volatile chemicals into sound.

“For instance, you have small molecules like acetic acid contained in vinegar or pungent formic acid emitted by some ants, they’re very volatile and diffuse into the air rapidly,” he says. “So, I thought it would be possible to translate a high or low volatility into high or low tones, as well as other chemical traits into other sound traits.”

Sawfly larvae release similar smelly chemicals when they are scared or in danger to deter predators. This provides a way to visualise – well, audify – these signals without having to do other expensive molecular techniques.

The other benefit is that it doesn’t need a lot of chemicals to start with, so Boevé says he hopes it can be used to collect data even if there is only a small quantity, especially when it’s the wrong season or difficult to harvest.


Read more: Butterflies feed on live young to steal chemicals for good sex


Humans creeped out by sound

To further explore how good these chemicals were at scaring off predators, the researchers played the sounds over a loudspeaker and measured how quickly and how far humans moved to get away from it. Some of the participants described the sounds as “creepy” or even “downright scary”.

According to the study, they moved away just like an ant would move away from a sawfly smell.

“Interestingly, we could show that the responses by ants and humans are correlated, thus indicating that sonification can approximate the ‘real world’ of predator-prey interactions,” says Boevé.

Normally, this technique allows patterns to be ‘heard’ in a large dataset, especially when there is a lot of noise (excuse the pun) from other sources.

“Examples of such phenomena are earthquakes in seismologic data, or network hacking in internet data streaming,” says Giot.

Is it still bizarre science? Absolutely.

“To be honest, I considered the sonification project so far-fetched myself that I set the project aside, sometimes for several months,” says Boevé.

The study was published in Patterns.

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