Brown Hairstreak Egg Hunt

With the butterfly season over you'd be forgiven for thinking we will now stop harassing you over the next few months to get out and record butterflies for our Sussex Atlas. Well I'm afraid you're wrong because the winter is the best time to record one of our most elusive species – the Brown Hairstreak.

Brown Hairstreak. Photos: Richard Roebuck

The records we received in 2010 of the adult butterfly, which flies in late summer, show that this species can turn up all over West Sussex and many amazed Sussex branch members reported sightings in their gardens and local parks. As I mentioned this butterfly is highly elusive – a fast flying resident of the treetops – so you may well have a colony near you and not know about it. We believe that the Brown Hairstreak is much commoner and widespread than the records suggest.

The winter months are the best time to get out in your garden or local park and discover if there is a Brown Hairstreak colony nearby because at this time of year the butterfly's distinctive eggs become rather obvious. All you need to know is where to look – and a hand lens or magnifying glass.

The Brown Hairstreak lays it's eggs on Blackthorn bushes and between late autumn and spring the blackthorn is without its leaves. Exposed on the dark bark are the white eggs of the Brown Hairstreak.

How to hunt for Brown Hairstreak eggs

Locate your nearest Blackthorn bush – whether it be in your garden, local park or while out walking in the countryside. At this time of year they've lost their leaves but not their long spines – so watch your hands!
Back in the summer the female would have laid her eggs – usually singly - at the spine bases or forks between twigs. They especially like the junctions between the new growth and the old wood and you should target your efforts lower than head height. Where new blackthorn suckers are shooting out from the ground on the edge of the bush check these too.
The eggs are like miniature sea urchin shells – rounded and intricately patterned - and only about 1mm in diameter. It sounds like these tiny white eggs would be impossible to find but their bright white colour really stands out on the dark twigs and their texture almost makes them sparkle in the winter sunshine. A lot of people remark how easy it is to find the eggs once you ‘get your eye in' – so give it a go. It's a great way to add some extra interest to a winter walk.
When you find one get out a hand lens or magnifying glass and have a close look at the egg – it's a miniature miracle of engineering! If you find rather elongated, smooth white eggs then these belong to the Blue-bordered Carpet, a moth which also passes the winter as an egg on Blackthorn. If you do find any of these moth eggs please send in these records too.
Blue-bordered Carpet and Blue-bordered Carpet eggs
When you find your eggs make sure you email me with your records (sussexgrayling@aol.com) - date, grid ref, number of eggs – and I'll stick them on our atlas map or send your photos and details to the sightings page of this website. Most of our adult Brown Hairstreak records are from the west of the county – but I'm sure we can find some eggs in East Sussex. One record this year came from north Shoreham – so you folk along the coastal strip are in with a chance too.