It’s not been a good four decades for the UK’s butterflies.

Those are the findings from the latest State of the UK’s Butterflies report to be published. The report, compiled by Butterfly Conservation and the Centre for Ecology and Hydrology, comes out every five years, but the latest edition also covers the period from 1976 to 2015.

And it reveals that over three-quarters of the UK’s resident and migrant butterfly species have declined in number and occurrence over the last 40 years, with some once common and widespread species now in severe trouble, joining some rarer species.

The reasons for the decline are not well understood but could include habitat loss, climate change and pesticide use. Scotland fared better than England, showing no long-term trends.

However, the report also shows signs of hope as a number of our most endangered butterflies are recovering thanks to conservation efforts, and that both common and rare migrant species have been arriving in larger numbers.

The findings utilise data gathered by two long-running citizen science projects: the Butterflies for the New Millennium recording scheme and the UK Butterfly Monitoring Scheme, and provide the government with its official statistics.

To help make sense of such a complicated document, Richard Fox, lead report author and Butterfly Conservation’s head of recording, has given BBC Earth the headlines from the report.

Wood white

Over three-quarters of UK butterflies have declined since the 1970s. For example, the occurrence of the wood white across the country has decreased by 89% since 1976, resulting in the loss of many colonies, and numbers at monitored colonies have also declined alarmingly: 88% since 1976.

Small heath

It is not just butterflies of special habitats that have declined. Increasingly, widespread species are in trouble too. The small heath, for example, is a very widespread grassland butterfly, not previously considered to be threatened in the UK. However, the new report shows that its trends in both occurrence and abundance have decreased by more than half since 1976: 57% and 54% respectively.

The wall

The wall is another widespread butterfly that has suffered severe long-term declines. It was once a common farmland butterfly but is now one of the UK’s most rapidly declining species. Trends for the wall show a 77% decrease in occurrence and 87% drop in abundance since 1976.

Red admiral

The migratory butterflies that visit the UK every year have increased since the 1970s. For example, the red admiral has increased in abundance by 257% at monitored sites and has become more widespread too (25% increase in occurrence) since 1976. It has even started to spend the winters here rather than migrating further south in Europe.

Ringlet

A minority of butterflies have done well in the UK since the 1970s, benefitting, it seems, from climate change. The ringlet, for example, has colonised large areas of northern England and Scotland. Its occurrence has increased by 63% and its abundance by 381% since 1976.

Duke of Burgundy

In contrast to the gloomy long-term picture, trends over the past decade provide grounds for optimism for some threatened UK butterflies. For example, conservation work targeting the endangered Duke of Burgundy butterfly has helped to stem the loss of colonies over the past 10 years and numbers have increased by 67% at monitored sites.

Pearl-bordered fritillary

The pearl-bordered fritillary is another endangered butterfly showing some positive recent signs of revival. Its abundance has increase by 45% and its occurrence by 3% since 2005, following severe long-term declines in both measures.

Gatekeeper

It’s not all good news for butterflies over the past decade. Some common species have shown unexpected declines. One of those is the gatekeeper, an abundant summer butterfly found in gardens, grassy areas and along hedgerows. Its distribution has remained stable, but its numbers have declined sharply – by 44% – in the past decade.

Essex skipper

Another butterfly of the wider countryside that has suffered a recent collapse in abundance is the Essex skipper. Its numbers are down by 66% over the past decade.

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