Butterfly numbers exploded in UK in early April

Butterfly numbers in the UK have ‘rocketed’, according to a report by The British Trust for Ornithology (BTO), which put the record number for some species down to an exceptionally warm beginning of April.

The BTO’s Garden Watch results have been spectacular, experts have said.

Butterfly numbers and when they emerge from hibernation depend on the weather, with spring being an important time of year.

Brimstone butterfly

Brimstone butterfly (Gonepteryx rhamni) numbers shot up in early April. (Image: BTO)

Poor March and super April

An unsettled March meant that reports of butterfly sightings were lower compared to March 2014. However, with the weather turning dry and abnormally warm at the beginning of April, butterfly numbers “shot through the roof,” according to the BTO.


Sightings of both Small Tortoiseshell and Brimstone butterflies were reported in 40% of BTO BirdWatch gardens at the beginning of April this year, compared to just one quarter in the same month last year.

The Brimstone butterfly was seen in one third of gardens, which is a record since 2003, when records began.

The biggest surprise was the Peacock butterfly, which was spotted in more than half of BTO Garden BirdWatch gardens (a record), compared to one third in April last year.

Peacock butterfly

The Peacock butterfly (Inachis io) was the biggest surprise. (Image: BTO)

Unfortunately, the good weather did not last, and butterfly sightings have declined rapidly.

BTO Garden BirdWatch team member, Clare Simm, said:

“As you can see, the BTO Garden BirdWatch is not just about birds. Our volunteers provide us with vital information on other taxa too, helping us to understand how important gardens are as a habitat for all wildlife.”

“If this unsettled weather continues, it may be bad news for butterflies so we need to keep an eye on how they fare over the rest of the year.”

Small Tortoiseshell

Small Tortoiseshell (Aglais urticae) numbers were also significantly up in early April. (Image: BTO)

You can help

The BTO wants to know whether the short spell of good weather in April was enough for British butterflies. It is asking members of the public to help it find out.

You can participate in the BTO Garden BirdWatch. Participants get a free enquiry pack and magazine. You can get in touch by writing to [email protected] , phoning 01842 750050, writiing to GBW, BTO, The Nunnery, Thetford, Norfolk, IP24 2PU or visiting bto.org/gbw.

Britain’s most endangered butterfly – the High Brown Fritillary – made a spectacular comeback in 2014, registering a population increase of 180% compared to the previous year.

Video – Spotting and identifying British butterflies

Matthew Oates, a National Trust Butterfly Specialist, explains how to spot and identify British butterflies.