Where to look
The green hairstreak is distributed throughout the UK but is localised and forms distinct colonies. It is found in a wide variety of habitats, including chalk downland, scrubby grassland, moorland and bogs, heathland and railway embankments. It also has a wide range of larval foodplants, including bilberry, bird’s-foot trefoil, broom, common rockrose, dogwood, dyer’s greenweed, buckthorn, cross-leaved heather, bramble and gorse.
When to look
The green hairstreak has one generation per year. Adults tend to emerge in late April and are on the wing until early July. Caterpillars grow quickly and develop into pupae in late summer which over winter and emerge as adults the following April.
What to look for
Males and female green hairstreaks are similar in appearance. They are relatively small butterflies. At rest, they always hold their wings shut showing their metallic green undersides. The brown uppersides of the wings are only seen when the butterfly is in flight.
Males are territorial and perch on shrubs waiting for passing females, darting out to investigate passing objects which could be females. Females spend their time searching for nectar sources and egg laying sites.
What the data will tell us
Information about where the species have been seen will tell us whether the distribution of these species changes over time. For example, green hairstreak has only been recorded below 500m altitude in the Peak District and so may move uphill as the climate warms. They may also alter the types of habitat they use. This is why giving an accurate location of your sighting is important.
Information about the date these butterflies were seen will also tell us whether the timing of events is changing in response to climate change. There is evidence that the emergence times of all of these species are getting earlier as temperatures increase.
Illustration (c) Chris Shields