Suddenly, painted ladies are everywhere. From roadside verges and patches of waste ground to the flowerbeds in my Somerset garden, I am seeing dozens of these attractive black, white and orange butterflies, as they flit from flower to flower, feeding hungrily on nectar.

They’re not the only butterflies currently on the wing. As the last meadow browns, pale and faded from the sun, straggle along the hedgerows, I’m seeing newly minted gatekeepers and common blues wherever I go. And, on a recent visit to my coastal patch, I came across two exquisite little butterflies, brown argus and small heath: the latter the 21st species of butterfly I have recorded there in less than five years.

This second (mainly) hot and dry summer in a row is good news for butterflies – and butterfly watchers. The charity Butterfly Conservation agrees: its latest statistics for the common blue show that last summer, numbers in England were up a whopping 110% on the year before. Butterfly Conservation predicts that this year’s hot weather could mean that the species will have its best ever summer.

But we should remember that butterfly populations have always fluctuated from year to year, depending largely on the prevailing weather conditions. To assess these figures more carefully, we really need to look at the long-term trends, which are rather less positive. For many of Britain’s favourite summer butterflies, including the once-common and familiar small tortoiseshell, there has been a steady decline over the past 40 years or so. This is due to a combination of factors, of which the most serious are the intensification of farming, combined with a more general fragmentation and loss of habitat.

Peter Marren, a naturalist whose latest book, Emperors, Admirals and Chimney Sweepers, tells the compelling story of the weird and wonderful names of our butterflies and moths, sounds a note of caution about the recent glut of sightings. While accepting that warm weather is good for adult butterflies, he points out that it may not be quite so favourable for their offspring, which often rely on a specific plant on which their caterpillars feed.

“Where butterflies come unstuck in prolonged hot weather is if their larval food plants dry up – for example, if the chalkhill and adonis blues find only stunted, dried-up horseshoe vetch to lay their eggs on.” As he points out, the famous long, hot summer of 1976 was a bumper year for these species, but the following year, 1977, a very poor one, as the majority of caterpillars failed to survive.

A red admiral soaks up the sun in Whitley Bay. Photograph: Owen Humpreys/PA

He also notes that the recent mass appearance of painted ladies – recalling the extraordinary summer of 2009, when tens of millions of these butterflies could be seen throughout the UK – has absolutely nothing to do with the weather here in Britain. Instead, it indicates that conditions were favourable on the fringes of the Sahara in Morocco, where these butterflies came from.

The ones we are seeing now are actually the offspring of an earlier generation, which arrived in the UK back in the late spring. These butterflies are now feeding to boost their energy levels in preparation for flying south again.

Research by scientists at Butterfly Conservation confirms that the long-term population trend of some of our most charismatic insects is indeed downward, with more than three-quarters of the UK’s butterflies and two-thirds of larger moths in decline.

This has a knock-on effect on ecosystems and species: cuckoo chicks, for example, rely on their host parents finding large moth caterpillars for them to survive. But partly because of the shortage of these, cuckoo numbers have dropped by two-thirds since the early 1980s, mirroring the fall in their food supply.

We need to know more about population trends in Britain’s butterflies – as we do for any declining species and groups – so Butterfly Conservation urges people to take part in the charity’s annual Big Butterfly Count. As its spokesperson Katie Callaghan explains: “This will provide a picture of how butterflies and larger moths have fared this year, compared with every summer over the last 10 years.”

The common blue has taken to the wing in record numbers. Photograph: Mark Searle/Butterfly Conservation/PA

Last year more than 100,000 people took part in the survey, logging almost a million individual butterflies during just 15 minutes of observations. This year’s count ends on 11 August, and so, weather permitting, you still have a chance to take part. As Sir David Attenborough, the organisation’s president, has pointed out, doing so helps contribute to our wider understanding of the UK’s wildlife: “The Big Butterfly Count is about more than just counting butterflies – we’ll be taking the pulse of nature.”

One of the biggest threats – and opportunities – facing Britain’s butterflies is the current climate emergency. And, as with any response to higher temperatures, there will be winners and losers. Common and adaptable species, such as the peacock and comma, have already begun to extend their ranges northwards into Scotland, and are likely to continue to do well as the climate heats up. But, as Marren points out, rare and localised species are less likely to be able to respond to change, especially if, as predicted, it changes the nature of their more specialised habitats.

The Big Butterfly Count is about more than just counting butterflies – we’ll be taking the pulse of nature David Attenborough

One example is the wood white, a delicate butterfly found in woodlands in a few parts of southern England and the West Midlands, where it can be seen fluttering along woodland rides and the sheltered edges of clearings. Although higher temperatures should in theory allow the wood white to shift its range northwards, its inability to cross large swathes of unsuitable habitat means that it is unable to take advantage of a warming world.

We would also expect that, as average spring and summer temperatures continue to rise, new butterfly species will cross the Channel, adding to our paltry total of fewer than 60 species (compared with almost 500 in Europe as a whole).

Yet despite the rise in records of continental European species such as the large tortoiseshell, long-tailed blue and the spectacular queen of Spain fritillary during the past decade, none has yet managed to establish permanent breeding populations here.

That’s in sharp contrast to other groups of flying insects, such as moths and damselflies, of which several species have successfully colonised in Britain. Surely it is only a matter of time before those new butterflies join them.

So, to sum up, some of Britain’s butterflies are enjoying the benefits of hotter-than-average summers – at least in the short term – while, as with all our wild creatures, they face an uncertain future in a rapidly changing world.

What is certain is that their loss would be a condemnation of our lack of stewardship of the natural world. For, perhaps more than any other living creatures, butterflies symbolise that rare combination of inspirational beauty and fragility, perfectly summed up by Marren in his book Rainbow Dust: “I believe that the flutterings [of a butterfly’s wing] can summon up at least a small breeze in the human soul. Let it blow … and let it remind we earthbound humans everywhere of the power and wonder of the natural world.”

Stephen Moss is a naturalist, author and lecturer based in Somerset

• Persuading butterflies to choose your garden is relatively simple: provide plants that produce the nectar on which the adults will feed

• Native wild flowers are often considered to be more suitable than non-native ones, but the real key is making sure there are nectar-rich flowers in bloom from April through to October

• Letting part of your garden go wild, with nettles, thistles, grasses and other “weeds”, will provide a place for caterpillars to feed and pupate, ensuring you have a new generation of butterflies later on

• In autumn, leave fallen fruit on the ground: painted ladies and red admirals love feeding on the fermenting juices

• Avoid using pesticides and chemicals. Check out Butterfly Conservation’s booklet, available when you join the charity, for more details.