Wet weather may cause butterfly numbers to decline

Chalkhill blue butterfly

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Butterfly Conservation's survey, the Big Butterfly Count, runs from 14 July to 5 August - peak butterfly season.

President of Butterfly Conservation Sir David Attenborough has warned that butterfly numbers may suffer because of wet weather.

"[It] has made life hard for... butterflies and things could get worse unless conditions improve," he said.

The annual survey relies on public participation and is thought to be the biggest in the world.

Spotted flycatcher carrying tortoiseshell butterfly In cool weather, warm-blooded predators have an advantage

In March, warm weather followed a mild winter and some spring butterflies emerged early, usually a positive sign for the insects.

Butterfly Conservation recorded the small blue on 30 March on the Isle of Wight, one of the earliest recorded sightings for the species, the charity said.

But early optimism was brought to an end by the April rain.

Now the mixed weather of last spring has given way to a cool, wet and windy summer, which could be bad news for butterflies, said Richard Fox, surveys manager at Butterfly Conservation.

Butterflies are cold-blooded animals and without warm conditions, they are vulnerable to predation and disease. Mr Fox said that this applies throughout their life cycle.

"When they're in the egg, when they're a caterpillar and when they're a pupa, everything about their lives is dependent on the ambient temperature of the outside world and their ability to warm up."

Marbled white on pyramidal orchid Part of the Nymphalidae family, the marbled white is one of the most distinctive species
Male skipper butterfly Named for its darting flight, this male skipper butterfly belongs to the Hesperiidae family
Holly blue butterfly The holly blue (Lycaenidae family) is a common garden visitor across southern England and Wales but is rarer in Scotland and the north
Male brimstone butterfly The brimstone, belonging to the Pieridae family, is one of Britain's longest-living butterflies
Swallowtail butterfly From the family Papilionidae, the swallowtail butterfly is a very rare sight in the UK. It is now only found in the Norfolk Broads

When the weather is cold, butterflies roost either low in the grasses or high in the trees, depending on the species.

Without warmth they cannot fly, so during bad weather they have no choice but to wait it out, explained Mr Fox.

"The adult butterflies may only live for a week or 10 days. If for eight of those 10 days it's pouring with rain and blowing a gale, then obviously their ability to find a mate and reproduce, lay eggs and travel around and find nectar and feed and all the rest of it, is greatly curtailed because they simply can't operate."

Butterflies in trouble

Painted lady butterfly on stone wall
  • Painted lady: Found on every continent except South America, these strong flyers are capable of long-distance migrations such as from north Africa to the UK
  • Common blue butterfly: Males have violet-blue upper wings, while females that inhabit the northern or western parts of the UK tend to be bluer than those in the south
  • Small tortoiseshell: One of our most familiar butterflies has experienced a rapid decline in the south
  • Brimstone butterfly: Males have yellow upper-wings while females are pale yellow-green, almost white in flight

The recent weather threatens a continuation of last year's downward trend of UK butterfly species.

Last year's Big Butterfly Count showed an 11% year-on-year decline in the average number of individual butterflies. Common blue numbers fell 61% and brimstone figures were 40% down.

"Our butterflies were already struggling - almost three quarters of UK species have decreased in numbers during the last 10 years," said Sir David.

The emergence of species such as the common blue usually takes place around May with the offspring of these butterflies emerging later in the summer, rather than waiting until the following year, explained Richard Fox.

"So there's a kind of double whammy for some of these species: that they were hit by bad weather during the spring and now potentially they're going to get hit again.

"You've got last summer's generation of adults not leaving many offspring, which then came out this spring. There have been even fewer of those and they've been hit by the bad weather... in June.

"They will probably have left even fewer offspring ready to come out in late July and August," he said.

These common blues will be among the species that the public are invited to tally up during the Big Butterfly Count.

"By taking part... you will be providing important information that could help turn their fortunes around," said Sir David Attenborough.

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