Why biting flies are attracted to blue objects? Unraveling the mystery

London, UK

Researchers at Aberystwyth University's Department of Life Sciences have discovered that biting flies are strongly drawn to blue objects because they mistake the colour for potential hosts they can feed on. This finding could have significant implications for controlling diseases transmitted by flies, such as sleeping sickness, by enhancing the effectiveness of traps.

Dr. Roger Santer, the lead researcher, explained that entomological field studies have long observed flies' attraction to the colour blue, leading to the creation of traps in that particular hue. 

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However, the reason why biting flies are particularly attracted to blue has puzzled scientists. Previous theories suggested that flies were drawn to blue due to its resemblance to shady areas or animals, but these had not been conclusively proven.

Artificial neural networks shed light

To address the question, the research team developed artificial neural networks that mimicked the visual processing in the fly's brain, specifically those of tsetse, stable, and horse flies. 

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The networks were trained to distinguish animals from leaf backgrounds and shaded from unshaded surfaces using the responses of the fly's five types of photoreceptor cells. 

They were then tested to classify blue flytraps.

Surprising results

Published in the Proceedings of Royal Society B, the peer-reviewed study's results challenged the theory that flies perceive blue as shade. 

The neural networks successfully detected shade through brightness, without misclassifying blue objects as shade. 

However, when it came to recognising animals, the networks compared the responses of blue and green-sensitive photoreceptors and frequently mistook blue traps for animals. 

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This led the researchers to conclude that blue objects, including traps, resemble potential hosts to flies.

Implications for disease control

Dr. Santer said that understanding the mechanisms behind flies' attraction to colored traps could lead to improved trap designs that more efficiently catch flies. 

This is of utmost importance since different species of biting flies spread diseases among humans and animals. Fly control plays a crucial role in disease control efforts. 

Diseases like human African trypanosomiasis (sleeping sickness), which is fatal without treatment and prevalent in sub-Saharan Africa, and the globally destructive stable fly could benefit from this research.

Field experiments support findings

Field experiments have further supported the team's conclusions. Tsetse flies captured in blue traps tend to show signs of not having recently fed, indicating their active search for hosts.