Small Heath ButterflyButterflies are one of the most sensitive indicators of the health of our environment.

Being as they are colourful, fairly easy to identify and have specific habitat requirements, food plants and nectar sources, they make ideal subjects for ecological study.

Today, Dr Val Perrin, a CRT monitoring volunteer at Lark Rise Farm completed a butterfly transect for Barton and Westfield. Despite seeing rather few butterflies, he recorded good numbers of one of our specialist species, the small heath. 11 in total between the two sites. This species is likely to benefit from the hot dry weather as they like short, sparse grass and the drought has reduced the lushness of the grassland.

Val also saw brown argus butterfly at both sites, I had seen one at Westfield the previous week but this species is now starting to build up its numbers. He also saw a common blue butterfly, but unfortunately he saw it outside the official count parameters.

Having completed their primary purpose of mating and laying eggs, the lower numbers of butterflies at the moment is a reflection that many of the early spring species are now fading away and dying. 

Groups of caterpillars of small tortoiseshell and peacock have started to be seen in the nettle beds along the banks of the brook and other places. The common blue, brown argus and small heath are all multi-brooded species in our area; the butterflies we see in spring, lay eggs which develop into caterpillars, and go through the growth phases rapidly to produce new adult butterflies in high summer.

The ‘second brood’ is generally much larger numerically. Their offspring go through the winter as caterpillars, but for some individuals development can be fast enough for a third brood in early autumn – particularly with small heath.

This flexibility in ecology allows them to occupy a wide range of habitats; further north or at higher altitudes the common blue species can only produce one 'brood' during the summer whereas, further south this species can produce up to three 'broods'. In hot years with long seasons (which 2020 is on course to be), three broods might be possible in a region where only two are the norm!

The small numbers of individuals of these multi-brood species that emerge in spring coincides with the time that most of the very early butterfly species are dwindling away – most of the early species, peacocks, commas and small tortoiseshells, have laid eggs and I have seen quite a few caterpillars of these species in nettle beds already.

After the abundance of butterflies through April and early May, the total numbers are now quite a bit lower. Traditionally this period was known as the “June Gap” as it comes before the big emergence of later-flying species such as meadow brown, gatekeeper and large skippers which are still feeding on grasses at this time.

This year the gap is starting a couple of weeks early, and there are reports of one or two early emerging individuals of species we might expect in high summer, showing how the changing climate is affecting our wildlife. The regular monitoring we participate in reveals these effects and is of huge value in understanding the implications of global warming.

Dr Vince Lea
Head of Wildlife Monitoring 

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