Egg hunting

Friday 17 March 2023

Conservation trainees

https://www.facebook.com/worcestershirewildlifetrust

Follow our four Conservation Trainees as they learn the ropes and develop skills for a future career in conservation...

Volunteers searching for brown hairstreak eggs by Jasmine Walters

Carolyn goes in search of an elusive butterfly...

Among the hedgerows of Lower Smite Farm, if you look close enough with a hand lens you may spot a white dot on the blackthorn. If you're lucky, this will be an egg of the brown hairstreak butterfly. Their eggs are white, circular and pinhead-sized and are found on young blackthorn shoots at the base of thorns or suckering blackthorn at the hedge bottom during winter. Eggs are laid in late August and September and remain where they are throughout throughout winter - they'll be hatching in just a few weeks time.

During winter Romy, Catharine and I had the honour of joining the farm volunteers in surveying for brown hairstreak butterfly eggs. We split into two teams to search along the blackthorn hedgerows of two fields searching through hand lens for any sign that the brown hairstreak has used this habitat. On the day we were out with the volunteers luck wasn't on my side (although Romy and Catharine found eggs in their section, which were mapped so they can be monitored). I found white eggs but they turned out to be from blue-bordered carpet moths. These weren't the only wild signs that we found - Catharine helped to find a number of harvest mouse nests.

Brown hairstreak egg and caterpillar on a stem by Paul Meers — Brown hairstreak egg and caterpillar by Paul Meers

With April nearly here, the larvae will be almost ready to break out of its protective casing. During your spring walks, see if you can spot the the slug-like pale green with yellow stripes caterpillars munching away at blackthorn leaves (beware - they are masters of camouflage). If you're patient enough, they can be easier to find in late June before they spin themselves into a chrysalis in early July. These dark brown featureless chrysalids are impossible to spot as they lie among the leaf litter or amongst crevices on the ground, where they are sometimes attended to by ants.

In late July, a brown hairstreak adult butterfly is born. These elusive butterflies can be seen fluttering around high in the canopy of trees in late summer. If you’re ever lucky enough to see one, it's likely to be a female who has descended to lay eggs. At rest, they usually close their wings, exposing the bright golden underwings that are crossed by two thin white lines and a distinct tail (females tend to be richer gold with longer tails). Wait for the sunshine to weaken to see them open their wings to reveal their deep brown colouring. Males have faint yellow patches on their forewings whereas females have large orange blotches.

Brown hairstreak butterfly feeding on cream coloured umbel flowers by Jill Orme — Brown hairstreak butterfly by Jill Orme

Brown hairstreak butterflies start seeking a mate in mid-August. Look up into the tops of ash trees to see if you can spot small clusters of adults fluttering around. The males stay high, obtaining their food from aphid honeydew among the tree tops, whereas females only descend to lay their eggs on young prominent growths.

These butterflies prefer to be in hedgerows, open grasslands and woodland edges that have dense amount of scrub where there is a high density of blackthorn. Over the last couple of decades, they've spread out from their hotspot of Grafton Wood across the eastern side of the county and volunteers from Butterfly Conservation are now tracking them into Worcester.

This success is due to efforts of volunteers and from organisations like the Trust. These elusive butterflies have faced many challenges and are listed as a species of conservation concern. Poor long-term agricultural practices have resulted in hedgerows being removed or cut every year, removing young blackthorn that the butterflies may have laid their eggs on. In many woodlands, the reduction of coppicing as a management tool has resulted in there being less sunlight for blackthorn to thrive. Supported by environmental stewardship schemes that provide grants for farmers to cut hedges on rotation rather than annually, volunteers from Butterfly Conservation have encouraged local land managers to make this change. The Trust have reintroduced coppicing in woodlands that they've bought and at Lower Smite Farm, for example, the farm volunteers have laid 150m of hedgerow. Management of the remaining hedgerow takes place every two to three years so that hedgerows are left uncut for the young blackthorn to grow. When cutting does take place, no more than a third is cut in any one year.

So when you're next out and about near a young blackthorn hedgerow, take a look and see if you can spot a brown hairstreak.