A lifetimes experience and as someone who they seem to love tells me that they don’t like it too cold. Or too hot. The latter is rarely an issue, though. My last trip (just back) was a bit too early for them, but they were just beginning. The nights were still cold, and I could enjoy sunrise without them, as it was still chilly. But, as soon as the sun rose and warmed up the grass around my tent, a few began to appear. And my last stop, at a bothy north of Diabaig, saw the first clouds of them begin to appear as the sun began to drop, after an extremely hot day. Not surprising as Craig bothy sits in a bog, really. But easily avoided by climbing up a bit on to higher ground where there was a bit of breeze. They don’t like wind and will disappear as it rises. I lit a fire in the firepit and that kept them away too. Some areas are notorious for them. Like Glen Affric. Have seen huge clouds of them there, and had friends riding out on the track to the hostel there, pursued by them well after dark. They love sheltered, damp, mild conditions. So it depends on where you are and what weather you’ve got. Just take lots of Smidge or Skin so Soft.