A Butterfly Enjoying the High Life

The Brown Hairstreak is, unsurprisingly, a brown butterfly, with beautiful golden-brown wings—especially the females. This makes both the males and females incredibly difficult to spot in the hedges.

Unlike many butterflies that flutter around garden flowers, Brown Hairstreaks spend most of their lives high up in the canopies of trees and hedgerows. They tend stay in the master trees (often Ash), because they eat honeydew from aphids and use the more open space to display and find mates. Because they rarely descend, getting an accurate head count of the adults is nearly impossible.

Why We Look for Eggs, Not Wings

Because the adults are so elusive, we’ve had to get creative. The Brown Hairstreak is much easier to find as an egg than as a flying adult. During the winter months, our dedicated teams of volunteers help search the Blackthorn scrub for tiny, pinhead-sized white eggs. 

This is where the red wool comes in, serving a key purpose. The wool marks where an egg has been found so we don't count them twice, ensuring our data is accurate. 

A Wiltshire Success Story

Colonies of the Brown Hairstreak in Wiltshire are dispersing. In the North of the county we see populations of Brown Hairstreak moving into other locations meaning they are finding more suitable habitats. In the South, the numbers are less dense, but we are seeing a wider dispersal. We are even seeing them appear in new locations, such as Cockey Down and Ham Hill, where they haven't been recorded before.

This success is down to careful and sympathetic management of hedgerows in the North and scrub in the South along with us. The recording of the butterflies lets us know whats working so is key to our conservation work and we are extremely grateful to our dedicate team of recorders. 

The Goldilocks of Butterflies

Brown Hairstreaks are picky, not only laying their eggs only on just one type of plant, but also only laying their eggs on the first year of growth on Blackthorn. With this in mind, we are more mindful about our cutting regimes. By only trimming our hedgerows once every four years and scrub on rotation, we ensure there is always a fresh supply of new growth for the butterflies to use without too much disruption to the eggs. This careful management of scrub and hedgerows across the south of the county is helping these butterflies disperse and claim new territory.

If you see the red wool now, here is what is happening behind the scenes.

In April or May the eggs will hatch into tiny caterpillars and begin feeding on Blackthorn leaves. By early summer, they will descend to the ground to pupate, and by late summer, the adults emerge to fly until September, starting the cycle all over again.

So if you spot some red wool during your next visit, please do not disturb it. Each piece of wool represents a future butterfly and helps us keep Wiltshire’s hedgerows and scrub full of life.