Why do flies hover beneath ceiling lights even when they have not been turned on

Question

..... and why do they perform that dance of triangles and squares in alternating directions?

Answer 1

they hover near lights for a heat souce

Answer 2

heat

Answer 3

cos theyr not stupid theyr waiting for you to  turn the light on, they

dont  call them fly for nothing.

Answer 4

I always wondered this - I am now pretty much certain it is because the light makes a good perch when they want a rest, that's why they congregate there.  It's pretty much free from disurbances such as people and pets!