Longhorn beetles have been climbing high to mate this mid-summer on Ben Lomond, according to the mountain's owners the National Trust for Scotland.
Visitors to the summit of the Scotland's most southerly Munro, one of 46 in the care of the conservation charity, reported the phenomenon to National Trust for Scotland ranger Fraser McKechnie who was carrying out path repair work on the hillside at the time.
Fraser said: 'The two banded longhorn beetle has an annual lek of sorts on Ben Lomond. It seems to head for the summit when the sun shines.'
'Lots of folk were complaining of masses of cleggs on the summit. It was of course, our friend, the harmless longhorn.'
Experts confirm that this behaviour is not confined to Ben Lomond's longhorn beetles (Rhagium bifasciatum), and that the same phenomenon has been observed at other sites across Scotland, Wales and the Lake District.
It is thought to be caused by high pressure bringing gentle updrafts which carry insects from wooded valleys up the mountains.
Rhagium bifasciatum, sometimes called the two-banded longhorn beetle, is one of the most common longhorn beetles in Europe. It can reach 22 millimetres (0.87 in) long and can be distinguished by the two prominent pale yellow bands on each of the elytra. It lays its eggs in dead wood, mostly of coniferous trees, where they bore deep, broad tunnels until they are ready to pupate after about two years. The adults feed on a wide variety of coniferous and broad-leaved trees. Unlike cleggs (horse flies) there's nae danger of them biting you.