12:07PM BST 12 Jul 2012
The presenter and President of Butterfly Conservation said rare species like the high brown fritillary could be wiped out by the recent wet weather. Even common species like tortoiseshell and peacock could be severely affected.
The situation could be as bad as the floods of 2007 or drought of 1976, when the butterfly population crashed.
Butterflies cannot fly in wet weather and therefore struggle to breed.
He said such "extreme weather events" as the recent floods are likely to become more common because of climate change.
"In my youth I remember 50 red admirals and tortoiseshells on a butterfly bush now I am lucky if I see one," he said.
Although ten species of British butterfly are benefiting from global warming by spreading into new areas, most will struggle with droughts and more heavy periods of rain.
Almost three quarters of the 57 species found in the UK have decreased in the past ten years. These falls are worrying because butterflies are a key indicator species for our environment and their decline suggests a wider insect biodiversity crisis.
Sir David explained that climate change is having such a negative effect because habitat has been severely reduced by building roads and concreting over the countryside.
He said gardeners can help to do their bit by creating new habitat. Good feed plants include knapweed and cowslips. Nettles are also a good feed source for four species, although it must be a large patch in the sunshine to really help butterflies.
Like the Prince of Wales, Sir David said he already has a wild flower meadow in his garden with ragged robin, ox-eye daisies and yarrow.
He even said councils, hospitals and businesses should be planting wild flower meadows on round-abouts, car parks and road verges rather than "regimental rows of geraniums and delphiniums".
"I much prefer wild species to cultivars and it encourages wildlife. Not only insects but birds and mammals," he said.
Sir David also called on people do "do their bit" by taking part in the Big Butterfly Count www.bigbutterflycount.org from 14th July to 5th August.
"The wet weather this spring and early summer is already has made life really hard for our butterflies and things could get worse unless conditions improve," he said.
"You can play a vital role in the battle to secure their future."
The Big Butterfly Count, now in its third year, aims to build up a picture of the state of butterflies in Britain.
At the moment butterfly numbers are only recorded on nature reserves but the count gives an opportunity to show how healthy the population is across parks and gardens.
