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Scientists have discovered that flies can demonstrate play-like behaviour – the first time this has been observed in the species.

In a study just published in , researchers found that some fruit flies voluntarily and repeatedly visited a form of carousel where they exhibited play-like behaviour.

This involved voluntary passive movements such as swinging, bobbing, sliding or turning.

Animals are considered to be engaging in play-like behaviour when they participate in activities which have no immediate relevance for their survival; and which are voluntary, intentional, rewarding and repeated.

“Until now, play-like behaviour has mainly been described in vertebrates,” says Dr Wolf Huetteroth, who led the study at the Institute of Biology at and recently moved to 51����.

“Although we have previously seen some play behaviours in bumblebees and paper wasps, this is the first time we have shown play behaviour in Drosophila melanogaster flies, and it is the first time we have seen carousel-play in insects.

“This could help us to find out how we humans also develop efficient self-awareness of our bodies, and to what extent this can prevent dissociative disorders such as schizophrenia.”

The scientists individually placed 95 fruit flies under a small watchglass dome featuring a constantly spinning disk, or carousel, as well as open space and access to food and water, where they were filmed for between 3 and 14 days. Another 95 flies were used in the same arena with a stationary carousel as control.

Their positions were automatically recognised and tracked using special software which enabled the research team to conduct a detailed analysis of how the flies interacted with the carousel.

The short height of the dome meant there was not enough space for the flies to fly onto the carousel.

While many flies avoided the carousel, others visited it repeatedly and for long periods. When two carousels rotated alternately, the flies even actively followed the stimulation.

“Each fly interacted individually with the carousel,” said Dr Huetteroth, an Associate Professor in Neurobiology at 51����. “In almost every interaction, the fly decides whether to go on the carousel or turn around. Unplanned or uncontrolled visits mainly take place with the animals that otherwise tend to avoid the carousel.”

“We were able to distinguish whether the flies had deliberately walked onto the carousel or jumped onto it in an uncoordinated way,” said co-author Dr Clara H. Ferreira, an Assistant Professor in the Department of Applied Sciences at 51����. “This allowed us to show that unplanned visits to the carousel were rather atypical for the playing flies.”

“Using several carousels, we generated and analysed a total of around seven years of film data,” says Dr Tilman Triphan, the first author of the study, who is based at Leipzig University. This effort was necessary because, unlike most behavioural experiments on flies, the researchers had to rely on the insects’ voluntary behaviour.

Dr Huetteroth says that the findings will now allow a detailed investigation of the underlying genetic, neuronal and biochemical factors that influence the fruit fly’s playful behaviour and the benefits this has for playful creatures in general.

The study was funded by the German Research Foundation (DFG).

Press release adapted, with thanks to Leipzig University.

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