Why does heat make us sleepy? Fruit flies ‘programmed’ to take naps may hold the answer

A brain ‘thermometer’ offers some clues, reports Tom Batchelor

Many people enjoy a nap in hot weather (Alamy/PA)

The Spanish love a siesta, while in the UK a summer heatwave is the perfect excuse for an afternoon nap. But the reason hot weather makes people sleepy is not fully understood.

Now, however, neurobiologists at Northwestern University in the US state of Illinois have turned to fruit flies (Drosophila) for the answer.

Analysing the insects’ brain “thermometer” circuit, they found that neurons receiving information about heat are part of a wider system that regulates sleep.