In 2018, the Great North Wood project team began two new regular transect surveys at One Tree Hill and Streatham Common. These are weekly, set routes that are devised in conjunction with Butterfly Conservation (Surrey and SW London Branch in this area) and provide data to the UK Butterfly Monitoring Scheme, helping to track national and local trends in these much-loved insects.

London Wildlife Trust launched the Great North Wood project in 2017, supported by Heritage Lottery Fund, and now works with volunteers, community groups, landowners, and councils, to revive and reimagine this ancient landscape as a home for nature and people.

We would like to express our gratitude to the 11 volunteers that shared the new weekly butterfly surveys between them this year, as well as the regular volunteers at Sydenham Hill Wood who continued with their established survey route.

The surveys and species

Recording butterflies on a weekly transect route for six months sounds like an arduous task, but as those who gave their time to help with our new surveys at One Tree Hill and Streatham Common can attest, it quickly becomes a labour of love. The necessary tedium of a blustery, overcast day with very little to be seen (a blank record is still valid!) is quickly forgotten in a thrilling glimpse of an exotic painted lady, some scrapping and tumbling skippers or a powerful flypast from a comma (pictured above) in the warm summer sun.

Walking a set route weekly at each site, recording butterflies in a 5m band (5m in front, 2.5m either side) the volunteer surveyors were accompanied for most of their journey each week by the ubiquitous speckled wood. If you take a walk in your local wood next summer this is the butterfly you are most likely to see, as it flies in the dappled sunlight that filters through the canopy, feeding on honeydew (an excretion from aphids) and chasing rivals in an upward spiralling motion.

One of the delights of running a frequent and consistent survey is to see the species come and go, as their differing life cycles mean that varying adult butterflies are on the wing at any given point in the season. The advanced party of orange-tips in early May gave way to gaggles of holly blues. These were followed by a midsummer of bustling large skippers and fluttering ringlets in the sunnier patches, interspersed with dependable meadow browns and gatekeepers. The butterfly year was closed out at Streatham Common by delicate small coppers (pictured below) enjoying rough patches of thistle, while flamboyant red admirals (which can overwinter as an adult) enjoyed the September sunshine at One Tree Hill.

Purple hairstreaks: flagships of the Great North Wood

Deriving its name from its purple-splashed upperwings and the white hairline scrawl on its underwings, the iconic purple hairstreak is one of the ‘flagship species’ of the Great North Wood project (along with oak, hornbeam, woodpeckers and stag beetles). Although not thought to be rare, this butterfly is under-recorded due to a life-cycle that revolves exclusively around the canopy of oak trees, and as a result it is not often picked up by surveyors walking transect routes. Oak is the foodplant of its caterpillar (caterpillars feed on different plants depending on the species) and adults feed on aphid honeydew.

However, in previous dry summers, the adults have been recorded much more frequently at ground level, something presumably related to the lack of moisture. The long, hot summer of 2018 provided this spectacle again, and purple hairstreaks were recorded down at ground level frequently throughout their adult flight period in late June and into July. It was a magical sight for those who were lucky enough to see them, and if 2019 should bring another dry summer then be sure to keep an eye out for purple hairstreaks wherever you see oak trees!

Another highlight of the season was the rarer white-letter hairstreak at Streatham Common – its caterpillars feed on elms, including the disease-resistant cultivar elms by the Rookery cafe. The large, yet graceful, silver-washed fritillary made further appearances in the ‘tennis court glade’ at Sydenham Hill Wood, as it has done over the last few years, and the continental painted lady showed up fleetingly at One Tree Hill. Unfortunately, the small tortoiseshell was not frequently recorded, tying in with rising national concern over the status of this typically common and widespread butterfly.

Butterfly walks

As well as the regular surveying, the Great North Wood team make sure to put on public butterfly walks to engage people with the butterflies around them. Beginner walks were run at One Tree Hill and Grangewood Park this year, as well as an evening walk at Streatham Common to enjoy the numerous purple hairstreaks. Look out for similar events in 2019!

Get involved

If you have an interest in butterflies and would be willing to help share weekly surveys at either One Tree Hill or Streatham Common, please get in touch with us in good time for the next survey season beginning in April 2019.

Learn more about our Great North Wood project.