Purple Hairstreak

The Purple Hairstreak (Favonius quercus) is a fascinating, often overlooked butterfly in Scotland, known for its elusiveness and high-canopy lifestyle. 

Here are the most interesting facts about this species in Scotland:

• Tree-Top Specialists: They spend almost their entire lives at the top of oak trees, rarely coming down except in high winds or droughts, making them hard to spot.

• Expansion in Scotland: Once thought very rare in Scotland, the Purple Hairstreak has seen a significant increase in records and is expanding its range, particularly in south-west Scotland and the Central Belt.

• Evening Activity: Unlike most UK butterflies, the Purple Hairstreak is most active in the evening (5pm–8pm) on warm summer days, often flying when others are settling down.

• "Seagull" Diet: Adults don't feed on flower nectar, but rather on honeydew—a sugary substance secreted by aphids high up on oak leaves.

• The "Sea Urchin" Egg: In winter, they exist as eggs that resemble tiny, spiky sea urchins, laid near the terminal buds of oak twigs.

• Unique Scottish Sightings: As of 2020, they have been recorded in new areas after long absences, including sites in Glasgow, South Lanarkshire, and as far north as the Highland region.

• Winter Detection: Because they are so hard to spot, conservationists survey them in Scotland by looking for eggs on "wind-blown" oak twigs after winter storms.

• The "Purple" Myth: Males have a brilliant purple sheen on their upper wings, but it is rarely seen. The underside of their wings is a quiet, silvery-grey, which is what you mostly see.

• Ant Connection: The caterpillar, which lives on oak buds, has been found to have a relationship with ants, which protect them, and in return, they produce a sugary substance for the ants.

• Habitat Independence: A single, isolated oak tree in a park or hedge can support a small, self-contained colony. 

Best time/place to see them in Scotland: In sunny conditions during late July or August, scan the highest branches of large oak trees (particularly Sessile or Pedunculate Oaks) with binoculars, looking for small, fast-moving silhouettes.