Exotic butterflies and moths from the continent have begun to colonise Sussex following the heatwave, experts have said.

Increasing numbers of the rare migrants are believed to have been drawn to the UK by the spell of hot summer weather and warm autumn temperatures.

The European Long-tailed Blue has raised broods at a swathe of sites along the south coast.

It is the first time it has bred over such a large area - the butterflies have been observed at a site in  Newhaven in Sussex, as well as Wiltshire, Dover and Margate.

Sussex Wildlife Trust's senior ecologist Graeme Lyons described how he spotted two in Seaford on Sunday on his blog. 

He said: "I pulled in, grabbed my bag and ran up the slope straight up to my first ever Long-tailed Blue! Before I knew it, TWO males were flying around my head fighting. What an incredible experience!"

He added a fellow naturalist, Neil Hulme, had spotted seven, making the town a hotspot for the butterflies.

Rare moths including the Clifden Nonpareil and Rosy Underwing have also appeared across several southern counties, including Sussex, Dorset and Hampshire.

Richard Fox, of the Butterfly Conservation charity, said: "These sightings are very exciting news, not only for the people lucky enough to see these thrilling butterflies and moths in the wild but also for the future.

"The hot summer enabled Long-tailed Blues and other migratory butterflies to spread northwards into Britain, capitalising on opportunities to breed here while the weather remains warm.

"This species probably won't survive the forthcoming winter, but it seems likely that the stunning Clifden Nonpareil and possible even the Rosy Underwing, have already established footholds in southern England."

The Clifden Nonpareil, first recorded in Clifden, Buckinghamshire, boasts a striking blue flash on its wings. It is the largest of the underwing moths - a group famous for the vivid dashes of colour that are used to ward off predators - and is recognised by a striking blue flash.

The large Rosy Underwing has only been seen on 10 occasions in Britain prior to this summer and raise the "tantalising prospect that the moth is now locally resident," the charity said.

"These sightings suggest that all three species may be attempting to colonise southern England and come as the autumn moth migration gets into full swing bringing rarities such as the Crimson Speckled and the Vestal to our shores from Southern Europe," a spokesman added.

Dorset-based moth recorder Les Hill has spotted three Clifden Nonpareil moths in the past two weeks in the same part of south Dorset.

"Clifden Nonpareil is one of the most charismatic of British moth fauna and is on every moth recorders' wish list," he said.

"As the name nonpareil states, it is peerless and has no equal. To record one in a lifetime is the fulfilment of an ambition; to record them every year in my garden is just remarkable."

Surprises this summer also included an influx of Vestal moths typically found in North Africa and Southern Europe. Experts have not seen such high numbers of this delicately-patterned moth entering the UK for half a century. This autumn it has been found as far north as Scotland and Northern Ireland.

Higher than average numbers of the exotic Crimson Speckled moth have also been recorded along the south coast.