‘Hangry’ male fruit flies attack each other if they go without food


A fruit fly sitting on a peach

blickwinkel / Alamy

If you’ve ever been hangry – so hungry you become angry – you have a little something in common with fruit flies. When these insects don’t get enough to eat, they aggressively lash out at others and some even make a kind of fencing manouevre with their legs to fight with other fruit flies.

“Male fruit flies display aggression that they direct towards other fruit flies. They don’t show these behaviours towards females,” says Jennifer Perry at the University of East Anglia in the UK.

Perry and her colleagues separated virgin male fruit flies (Drosophila melanogaster) into five groups of between 58 and 74 insects. One group consisted of newly emerged adults that had not fed since their larval stage, while another was made up of flies that were allowed to feed throughout the experiment. The remaining groups were fed and then deprived for periods of 24, 48, or 72 hours.

At six to seven days old, pairs of flies from each group were placed together with food and monitored over 5 hours. The team observed the pairs 16 or 32 times over 5 hours to record their behaviour.

Flies deprived of food had became increasingly aggressive, which peaked at 24 hours without food. The aggressive flies would lunge at and chase each other or fence with their legs.

“I think we can all relate to feeling hangry after periods of food deprivation, and what our study shows is that these feelings extend across even very distantly related animals,” says Perry. “They share lots of genes for their physiology and behaviour with vertebrates, including humans. They’re a good model [for aggression] in that way.”

Even animals as seemingly simple as a fruit flies have complex social lives and respond to changes in their environment that affect the costs and benefits of social behaviour like aggression, she says.

Journal reference: Animal Behaviour, DOI: 10.5287/bodleian:xrO2DD55e

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