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Aerial maps covered by this survey
Butterfly Survey 1976-2020
Brown Hairstreak
Wingspan - 35 -38 mm
The arrival of the brown hairstreak in the study area in 2018/19 is not without anticipation or precedent. Chalmers Hunt records small colonies breeding on sloe in and around the Farnborough area in 1946, and much more relevant to the new colony, around Cudham in 1953. Eric Philp, however, records the butterfly as absent from Kent completely after 1971, so its re-arrival in nearby Keston is cause for celebration and analysis. Eggs have also been found across Elmfield in BR2 where there is a high density of Blackthorn (spinosa).
Habit: Male and female butterflies differ through a marked increase in the patches of scent scales the female displays on its upperwing, from the underside however a very similar set of patterns appear. The butterfly is on the wing long term from late July onwards and appears fleetingly, feeding on aphid honeydew around the breeding site, which in Keston, is on the extensive blackthorn or sloe bushes that have taken over as the hardiest among many of our field and roadside hedgerows.
Single brooded: over winters in egg form - laid strategically on sloe twigs, before the small greenish, louse like larvae emerges in April to feed among the fresh foliage. Pupation is after about ten to twelve weeks, the larvae fattening and darkening through several instars, then descending to the foot of the bush, the butterfly emerging quite late in the year - July./August.
*An egg search on Elmfield by the Idverde team in early 2022 found brown hairstreak eggs to be prevalent on the whole area where blackthorn (spinosa) grows as an outreach of the coppice planting thirty years ago. 2023 proved better with an exponential total of eggs in excess of 200 eggs distributed throughout.
I favour sleeving the eggs in muslin as an intensive breeding device and raised many butterflies accordingly in BC*
Larval Foodplant: locally, sloe - buckthorn
Status locally : Spreading North - assisted by climate change and recent avian decline 2021/2022 Judging from the hundreds of eggs found in 2018 by Fred O'Hare and associates, quite well established. My conjecture is that the decline and habit changes in the passarine population locally, through agricultural practices and other insideous stresses, may combine with an increase in the spread of foodplant. This spread seems a possible by-product of a shift in the atmospheric density of nitrogen, due to man made energy factors.
KES - Keston BC - Bromley Common
© 2018/19 Fred O'Hare, © Jeff Boswell (images)
© Rodney Compton