Butterflies could suffer serious population crashes this year following record-breaking wet weather, Sir David Attenborough has warned.Conservationists are worried that the weather may trigger extinctions as April was the wettest in a century. Extended periods of cold, wet weather has delayed butterfly appearances across the UK - almost three quarters of which are in decline.Sir David, who is President of the Butterfly Conservation, is urging the public to take part in a butterfly survey, the Big Butterfly Count, to track different species and see how they have fared following the damp months.It is feared butterflies may have suffered poor breeding seasons as a result, which could lead to population crashes later this year or next spring.Conservationists are drawing parallels with the wet summer of 2007 which resulted in widespread flooding across parts of the UK and saw butterfly numbers plummet.The results of this year's Big Butterfly Count will help assess the impact of the wet weather on our butterflies."The wet weather this spring and early summer has made life really hard for our butterflies and things could get worse unless conditions improve" Attenborough explained."Our butterflies were already struggling - almost three quarters of UK species have decreased in numbers during the last ten years. These falls are worrying because butterflies are important indicator species for our environment - their declines suggest a wider insect biodiversity crisis."You can play a vital role in the battle to secure their future. By taking part in the Big Butterfly Count you will be providing important information that could help turn their fortunes around."For the third year running, the Big Butterfly Count is taking place in partnership with Marks & Spencer as part of its Plan A commitment to be the world's most sustainable major retailer by 2015.Richard Gillies, M&S Director of Plan A, said: "This is our third year of partnering with Butterfly Conservation, and we are encouraging all of our farmers, customers and employees to take part in the Big Butterfly Count."After all of the wet weather we have had this year we need as many people to take part as possible; at M&S we really want to make a positive contribution to the environment and by helping to get as many people involved in the Butterfly Count we can get a better understanding of biodiversity and how we can all play our part to protect it."Last year, the public counted more than 320,000 butterflies. The data provided vital information - revealing that the average number of individual butterflies seen was down by 11% compared with 2010's figures.This year Butterfly Conservation wants to discover how garden favourite - the Small Tortoiseshell is faring after research revealed numbers were down across our countryside once again.