Bee and butterfly numbers have slumped after a tenth year of unsettled weather, National Trust experts have said.

Mild winter and spring weather led to extremely high grass growth, good for farmers with livestock and for making silage or hay, but bad for warmth-loving insects including common meadowland butterflies.

The assessment comes as the National Trust marks ten years of its annual weather and wildlife review, which is aimed at understanding how changing weather patterns are affecting wildlife at its places.

The conservation charity is working with its tenants and partners to reverse the alarming decline in UK wildlife, with 56 per cent of species seeing their numbers fall in the last 50 years.

Matthew Oates, nature and wildlife specialist at the National Trust, said: “Our rangers have had to work closely with farmers and graziers to get grazing levels right for these plants and insects. In many places it’s been a struggle, but at a handful of places like Somerset’s Collard Hill – home to the large blue butterfly – graziers have triumphed.

“2016 comes on top of an unsettled decade, with many species struggling in the face of climate change and more intensive farming practices.”

A mild winter, cold spring and mild, wet weather in May and June led to early summer grass growth at a rate almost a third faster than in previous years.

This meant twice the number of hay bales were collected at Packwood House in Warwickshire and 25 per cent more silage was made on Saddlescombe Farm on the South Downs. However early summer rain on the Hafod y Llan estate in Snowdonia meant farmers struggled to make hay or silage.

Meanwhile at Lytes Carey bumblebee numbers dropped 85 per cent on 2015 as wildflowers in the field margins were outgrown by grasses, butterflies struggled at Purbeck, Dorset, with marble whites down 73 per cent and common blues down 23 per cent.

Rob Havard, beef farmer and tenant at Croome Park in Worcestershire, said: “The warm weather in the summer encouraged a really good rate of grass growth and then as soon as it started to get a bit dry we had a little rain which was ideal to encourage further growth. We also enjoyed a variety of flowering plants as well.”

“This year we also saw plenty of activity in terms of wildlife with a good population of field voles which attracted kestrels and barn owls.”

In the past decade, National Trust nature experts have noticed that winters are becoming milder and summers wetter, affecting not just insects but their bird and bat predators, and many low-growing plants. Over the last 50 years more than half of UK species have declined.

Mr Oates said: “In the ten years we’ve been reviewing wildlife at our places we’ve noticed pulses of unsettled weather become the norm. We last enjoyed a good summer in 2006.

“Mild winters and periodically wet summers have seen common wasp numbers apparently slump in many parts of the country, along with common ‘meadowland’ insects like the common blue butterfly. This could have a knock on effect on the invertebrates, birds and bats that eat them. And what affects insects today could well affect us tomorrow.”

Climate change has had a clear effect on weather and wildlife in the last decade. The growing season has extended by almost a month, and warmer temperatures, higher levels of atmospheric carbon dioxide and a longer growing season are leading to vegetation growing more quickly,which is in turn causing a drop in carbon dioxide.

Mr Oates added: “Long term, changes in how we manage land has also led to wildlife declines – with more than half of species experiencing a drop in numbers in the last 50 years.

“But one of the great successes of the last decade have been the ways farmers and conservationists have worked together to reverse wildlife declines in many of our places.”

In south west England work by conservation charities and arable farmers to benefit wildlife have resulted in the rare cirl bunting increasing by more than 800 per cent since 1989. And at Longmoor in the Lake District, grazing has created a wet grassland habitat allowing marsh fritillary butterfly larvae to increase by 560 per cent in ten years.