The public is being asked to help track the UK's butterfly populations as conservationists warn many native species are in serious decline.

The online Big Butterfly Count survey aims to get a better understanding of which species are in need of most help.

Butterflies are sensitive to changes in environment and have seen a collapse in numbers in the past three decades.

More than three-quarters of the 59 species found in the British Isles are in decline, including the meadow brown.

The holly blue and gatekeeper are among the other butterflies once recently regarded as common species which are now believed to be joining the list in need of protection.

The survey is being run by the charity Butterfly Conservation and retailer Marks spencer as part of its environment commitment.

Adults and children are being invited to spend 15 minutes in gardens, woodlands, fields or parks between 24 July and 1 August and make a record of the butterflies and day-flying moths that they see.

The organisers hope the survey will help build up a better picture of the fortunes of the country's butterflies, and give an indication of the wider health of countryside and nature.