Thecla betulae

Valais, Switzerland, September 2006

Valais, Switzerland, September 2006

Brown Hairstreak
Thecla betulae

Distribution: N Spain, Ireland and S UK and eastwards through S Scandinavia, Central Italy and N Greece.

Identification: Distinctive. Rich underside browns with a wedge of darker brown bordered by white. Dark brown upperside with bright orange brown patch on forewing, usually absent in the male. The tails on the upperside are red in both sexes.

Flight time: July to September, most frequent from August to mid September but may be regionally and seasonally variable.

Habitat: Woodland or open places with hedges or scrub near good stands of Blackthorn (Prunus spinosa), the larval food plant.

Behaviour: Secretive butterfly (usually). Most colonies cover a large area and adults of both sexes spend most of the time hidden around tree tops. Males congregate around certain "master" trees, usually Ash, where as females drop down looking for egg laying sites and also for dispersal. Thus most of my encounters have been with females. Both sexes can be found feeding on flowers (Hemp Agrimony is a favourite) but it is recorded that honeydew excreted by aphids is the preferred source of sugars - way up in the trees.

Eggs are laid singly at around 1 or 2 meters above ground level. They are located at forks in the outer twigs of Blackthorn or at the base of buds where they can be found fairly easily throughout the winter.

Additional notes: Generally only found a few times in a season due to the low density of the colonies. However, late summer 2006 was a great year in Switzerland when 4 or 5 butterflies could be found together in a small area in early September.