Late emergence of spring butterflies by Vince Lea

Common Blue

Common Blue

Following the coldest spring for 50 years, what is happening to our summer butterflies?

It seems that the so-called June Gap, when the spring emerging butterflies are fading away and the high summer ones are yet to emerge from their pupae, is going to be filled with butterflies emerging several weeks late.

A good example is the Common Blue, a species which has responded well to the hay meadows created on Lark Rise farm. In a typical year, there are two flight periods in southern England – a May-June emergence which breed rapidly and are followed by their offspring usually around late July-early August. The high summer population is usually much larger. In long hot summers, there is time enough for these to produce a partial third emergence in September-October, but most of the offspring go through the winter as small caterpillars, ready to feed up in the spring and produce the butterflies of next May.

The first Common Blue records for Lark Rise in 2013 were on June 2nd, the 10th week of the butterfly recording period. 2012 was a washout but 2011was an excellent year for them, and the first was seen on the 9th May – butterfly week 6. In 2011, the peak spring emergence occurred around the end of May/early June, so unless the one seen on the 2nd June this year was the peak (and we hope not!) we are probably running 4 weeks late.

What happens next remains to be seen of course, but a late first brood will probably lead to a late second, with very little chance of a third. In northern Britain, where summers are shorter, Common Blue only has one brood, around the end of June, which shows that the species is flexible in its breeding system, and as long as the population isn’t wiped out by a bad year, they can regroup and start again.

Common Blue is just one of a group of species with a similar breeding strategy and all have responded similarly to the late start to summer – things like Small Heath, Brown Argus and Small Copper have all been appearing weeks late on our regular transect walks. By contrast, we are still seeing other species that would normally be finished by now, most notably Orange Tip, which is normally finished by June but this is still going strong.

It may not feel like global warming, with such a cold spring, but it certainly could be described as climate change, and our wildlife is having to adjust to the new vagaries of weather. Every year is different of course, but the run of variation lately could well cause long-term changes in the species profile of our countryside. It is probably climate change which has seen the local disappearance of Wall Brown, and the expansion in the population of Marbled Whites. Who can predict the next change?

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