Pollinators in the Making
Eggs and caterpillars are our future pollinators – in biodiversity-focused landscaping and horticulture, planting for egg laying and caterpillar feeding is as important as nectar-rich flowers.
Brown hairstreaks are elusive and beautiful butterflies – one of the rarest species in the British Isles. Brown hairstreak populations declined by more than 60% during the 20th century, but numbers are starting to increase again. They rely on both ash trees and blackthorn (sloe) bushes to thrive and complete different stages of their life cycle. We were excited to receive a report from a local butterfly enthusiast last year that he had found brown hairstreak eggs in The Regent’s Park.
Brown hairstreaks lay their eggs on blackthorn (sloe) bushes and hedges. The caterpillars of this species feed almost exclusively on blackthorn, so the adult female will lay its eggs on young foliage of a blackthorn bush in the autumn. When the eggs hatch in spring, the hungry caterpillars will have new leaf growth ready for eating, only a few centimetres away.
Blackthorn is a native shrub species and is brilliant for boosting biodiversity. It is the foodplant of black and brown hairstreak butterflies as well as many moths, including lackey, magpie, swallow-tailed and yellow-tailed moth species. It is one of the earliest plants to flower each year – from February onwards it provides food for many wild bees and hoverflies, including buff-tailed bumblebees and tawny mining bees. Its dense, thorny branch structure is an ideal nesting spot for small birds, who can pick up a caterpillar or two at close range when raising chicks, and will also eat the sloe berries that appear in autumn.
The brown hairstreak used to be widespread across the UK, laying its eggs in hedgerows, scrubland and woodland edge habitat. The loss of hedgerows and untouched scrub is likely to be a major contributor to the reduction in numbers of brown hairstreak butterflies through the last century.
In addition to blackthorn, brown hairstreaks also require ash trees to support their life cycle. Adult brown hairstreak spend most of their time flitting in the canopies of ash trees, where they drink honeydew – a sweet substance secreted by the aphids and scale bugs which colonise the trees. In untouched native habitat, blackthorn would be likely to be found growing at the edges of woodland which included ash trees, supporting brown hairstreak through all stages of their life cycle.
In brown hairstreak conservation, the plants that support both the caterpillars and adult butterflies happen to be eyecatching species – but what about when a biodiversity-boosting plant is unattractive and less desirable? Stinging nettles support a wide range of caterpillars, including those of some of our best-loved butterflies: red admiral, small tortoiseshell, comma and peacock. In managing the Royal Parks, we know that nettles are not hugely appealing to visitors, so we utilise areas of the parks that are less frequented or fenced off to allow native ruderal plants – including nettles – to grow. You can find out more about the wonderful weeds of the Royal Parks in this blog.
Want to get involved in butterfly conservation in the Royal Parks?
Join us on Saturday 18 January at our planting and citizen science day made possible thanks to players of People's Postcode Lottery. It’s a great opportunity to get out in the fresh air and learn about the amazing nature that you can find right in the centre of London.
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