On Monday 16 December 12 volunteers plus staff were joined by the Sussex Branch of Butterfly Conservation in an attempt to find evidence of one of our most elusive butterflies. In the UK we have 5 species of Hairstreak butterfly, all of which lead secretive lives. Four of these cagey creatures can be found on our Pagham Harbour reserve and despite being the largest, the hardest of these to find is the Brown Hairstreak.
The adult butterfly often rests with wings closed revealing undersides of orange-brown with two white streaks and small tails on the hindwings. The uppersides are brown, with the females sporting an orange band on the forewing. However, it spends most of its short adult-life high up in the treetops, basking in the sunshine and feeding on aphid honeydew. The females only descend to lay their eggs in the forks of blackthorn twigs, which are normally laid singly.
Brown hairstreak - Patrick Cashman (rspb-images.com)
The caterpillar is just as tricky to locate. Once it has hatched in spring, it immediately burrows into a nearby bud. Here it feeds and by the time of its first moult, the leaves of the blackthorn have unfurled. Now the bright green caterpillar is perfectly camouflaged resting on the underside of a leaf during the day, only becoming active at night to feed and returning to its resting place at dawn. It’s just as devious when comes to pupating, being a purplish-brown hidden among the leaf litter at the base of the plant.
New research is coming to light following the discovery that the caterpillars fluoresce under ultraviolet light which is making surveying this stage of their lifecycle much easier, but by far the simplest way to verify their presence is to look for their eggs. That said, they are of course tiny, but do stand out white against the brown leafless branches on which they are laid.
Brown Hairstreak egg - Luke Parham
Last year we found just three, so imagine our delight to find 20 of this priority species butterfly.