Ephemera dancia is a true Mayfly which is bucking decline
A mayfly is making a comeback on rivers in the central belt of Scotland following years of decline.
Invertebrate conservation group, Buglife, said it could be linked to lower levels of pollution because of a decline in heavy industry.
Ephemera danica emerges when the mayflower, or hawthorn, is in bloom.
Meanwhile, the Highlands could emerge as a stronghold for another riverfly, ameletus inopinatus, as it is pushed further north by global warming.
The public are being asked to participate in a survey of mayflies.
The Ephemeroptera Recording Scheme is recruiting the help of fly-fishing anglers and people who use moth traps to send specimens, in an effort to gauge the health of the species' populations and distribution in the British Isles.
Adult ephemera danica start emerging during the second and third week of May.
Stirling-based Craig Macadam, Buglife's Scottish conservation officer, said there were mixed fortunes for riverflies which have suffered years of decline.
He said: "The true Mayfly is making a comeback in the central belt of Scotland, somewhat bucking the trends for declines of riverflies in other parts of the UK.
"It's probably due to the rivers receiving less pollution from industry now that the iron founding and other heavy industries are all but gone in the central lowlands."
Climate change appears to be having an impact on the insects' behaviour and could eventually lead to one riverfly, which favours cooler temperatures, being pushed to more northern areas.
Mr Macadam said: "There's evidence from the south of England that flight periods have changed dramatically with some species now flying throughout the year - probably due to warmer weather and less severe winters.
"This is likely to happen in Scotland before long.
"I collected a mature nymph of the blue-winged olive - serratella ignita - from the Aberdeenshire Don in December a couple of years ago.
"This species usually disappears from samples by the end of September in Scotland, so this could indicate a second generation of this species."
He added: "Ameletus inopinatus - the upland summer mayfly - is thought to be retreating to higher altitudes as water temperatures increase.
"It is likely that the Highlands will be its stronghold in the future."