Identifying Confusion Species - The Hairstreaks

The Hairstreaks are a family of small butterflies that often have rather secretive traits, which makes studying them not as easy as some other butterflies. We currently have all five UK species of Hairstreak in Northamptonshire, the Green Hairstreak, the Purple Hairstreak, the Black Hairstreak, White-letter Hairstreak and the Brown Hairstreak. The Brown Hairstreak has only just recently colonised and is limited to a small area around RAF Croughton in the south of the county. The Green Hairstreak, being our only small green butterfly, is unmistakable so will not be covered in this guide. One very good way of looking for Hairstreaks is to stand and wait by their larval foodplants and look for any butterflies flying around them. The Purple Hairstreak uses Oak, and the White-letter Hairstreak uses Elm. Both the Black Hairstreak and the Brown Hairstreak use Blackthorn, however, they fly at very different times of year with the Black Hairstreak flying in early summer and the Brown Hairstreak in late summer. While these plants do give a very good indicator of what the Hairstreak species you have seen is, you can’t be 100% sure unless you get a good look at it. In the past, I’ve seen Purple Hairstreaks resting on Elms, Black Hairstreaks resting in Oaks and White-letter Hairstreaks resting on the top of Blackthorns! A pair of binoculars can be your best friend when looking for Hairstreaks and the timing of the day can make a massive difference too. Hairstreaks are often most active during the early morning and late afternoon, and rather than walk around looking for them it is normally best to find a likely looking Oak, Blackthorn or Elm and stand next to it watching the canopy for any movement.

The commonest Hairstreak we have in the county is the Purple Hairstreak so it makes sense to have a look at this one first. The Purple Hairstreak spends most of its time up in the canopy of Oak trees and although it will come to nectar it predominantly feeds on the honeydew secreted by aphids on the leaves of the tree. The most common view of the Purple Hairstreak is of the small silvery metallic butterflies that you can see flitting around the canopy, however, they will occasionally come down low so we can get a closer look. The Purple Hairstreak has a silvery grey base colour to the wings with a distinct orange spot by the tails on the wings as seen in the photo below.

Purple Hairstreak

Another very useful tip that is worth remembering is the Purple Hairstreak will very often bask with its wings open. The only other Hairstreak to do this is the Brown Hairstreak which is very rare and is currently limited to a small area around RAF Croughton. Female Purple Hairstreaks have distinct purple patches on the forewings but the males just have a purple sheen across the wings.

Purple Hairstreak

Brown Hairstreak

The upper forewings of the male Brown Hairstreak and Purple Hairstreak can be rather hard to tell apart at a distance. One thing to remember is the male Brown Hairstreak has distinct lighter patches in the middle of each forewing.

Brown Hairstreak

Female Brown Hairstreaks have distinct orange patches on the upper forewings. They can also have much longer tails than the males but these can quickly become worn away.

Brown Hairstreak

The underwing of the Brown Hairstreak is quite unmistakable and is a beautiful mixture of oranges and browns.

Brown Hairstreak

For the next Hairstreak, we will move onto the Black Hairstreak. The Black and the White-letter Hairstreaks do look quite similar but they have quite distinct differences. Neither of them basks with their wings open so the key to the identification is to study the orange band that runs along the outer edge of the hindwing. The Black Hairstreak has a distinct row of black dots running through it which can be obvious even when seen at a distance or if the butterfly is worn.

Black Hairstreak

The White-letter Hairstreak lacks these rows of spots as can be seen in the below photo. The white line in the hindwing also forms a distinct letter “W” which is what gives the White-letter Hairstreak its name.

White-letter Hairstreak