Flies are annoying and pesky during the day, but once it’s nighttime, they tend to stop buzzing around and just sit there. You might have even seen them perched on your ceiling or in the corner of a window, seemingly parked for a few hours in a state of semi-sleep. But where do flies sleep?
Researchers have been studying the nocturnal behaviors of fruit flies (Drosophila melanogaster) for decades. It wasn’t until 2000 that it was confirmed that they show sleep-like behavior at night, including sustained periods of immobility and a reversible increase in the sensitivity of their nervous system. This indicates that flies’ sleep is indeed similar to mammals’ (Hendricks et al. 2000; Shaw et al. 2000).
The similarities between fly and mammalian sleep are also evident at the molecular level, as flies’ brain activity changes dramatically during both sleep and wakefulness. Furthermore, sleep deprivation results in a similar stress response in flies as in mammals, with an increase in the expression of heat shock proteins and chaperones (Huber et al. 2004).
In order to better understand the mechanisms that regulate flies’ sleep, scientists have been searching for specific neurons in the fly brain responsible for triggering a sleep drive. To do this, they’ve used genetic engineering to make a small number of neurons in the fly’s ellipsoid body glow green when they fire. Then, they bred flies with these genes and watched them to see whether turning on these neurons would cause the flies to sleep more, which is exactly what happened.