Dragon Flies enjoying a sun bath and a query

When out for a walk on a stretch of moorland in the Draperstown district early in September, on a day exceptionally bright and warm, with the sun shining in an almost cloudless sky and the pollen rising from the blooming heather at every footfall, I saw a most interesting sight. My way lay past a couple of outcrops of rock, the first exhibiting nothing unusual, while the second consisted of a highly indurated silicious rock carrying a large proportion of ferrous oxide, the heat radiating from the numerous minute sparkling crystals which it contained. Resting on its warm surface, or gliding above numerous Dragon Flies, perhaps 40 or more. They quickly disappeared when disturbed, but returned again to their hovering sunbeam dance above the rock when I had walked past. The puzzle is, how did these insects know to come from different places, and probably from considerable distances, to that particular rock. Have they natural means of sending a wireless call to each other, or can they feel the effect of the dancing beams or rays of light far beyond the effect of heat radiation, or were they guided by sight alone?—“G. B. McKeown”’ (Draperstown).