Scientists can't explain their change of colour, while even the most ardent bug hunters rarely get to see one.

Now two budding naturalists have found a pair of rare pink grasshoppers, close to the site of a major heath fire that devastated a Norfolk nature reserve.

Noah Battelley and Meg Willis, both seven, spotted the inch-long creatures at Dersingham Fen, close to their homes in the village.

They made the discovery three months after a major heath fire tore through the fen, destroying several acres of undergrowth.

'We were looking around for other grasshoppers in the woods near where the fire was,' said Noah. 'We spotted them then. There were two of them.'

Meg added: 'We kept them because Noah was having a sleepover at my house. I've got a bug hunting kit with a little jar and when Noah's mum came to over to pick Noah up, they took one with them.'

Noah's mother Helen said the youngsters, who both go to Sandringham and West Newton Primary School, were both accomplished bug hunters.

'From when Noah was about five, we started finding things he'd put in his pockets,' she said. 'We've found crabs and things like little dead birds.'

Then there were the crayfish, sighed Mrs Battelley. The ones Noah found during a family holiday to southern Spain, which stank the car out for most of the long drive home, until the source of the smell was traced to the door pocket where he'd hidden them.

As Mrs Battelley shuddered at the thought, Noah and Meg were already planning their next bug hunting trip - in search of stag beatles.

Expert Matt Shardlow, from conservation group Buglife, said pink grasshoppers were a 'genetic abnormality'.

'For some reason you get some which are pink, where they'd normally be green or brown,' he said.

'If you go out looking at grasshoppers a lot, you'd expect to see one or two a year.

'In terms of percentage, it's a tiny proportion of the number of grasshoppers - less than one per cent.'

Mr Shardlow said a number of different grasshoppers sometimes came in pink versions.

'If it's a pale-ish pink, it's likely to be a meadow grasshopper,' he said.

'Other species, like the field grasshopper, quite commonly have pink versions.

'It's part of the natural genetics of these populations but we don't know why.

'We don't know of any evolutionary advantage being pink would give you as a grasshopper.'