Brown Hairstreak Egg Hunt

21 March 2018 | Posted in Charlotte Owen , Insects
Brown Hairstreak Egg Hunt
brown hairstreak eggs © Bob Foreman

by Charlotte Owen

WildCall Officer

It may not seem like the best time of year to be on the lookout for butterflies but there are some tiny treasures out there just waiting to be discovered.You'll need to brave the cold to seek out a patch of blackthorn, equip yourself with a magnifying glass or hand lens, and prepare to be patient as you painstakingly examine the bare twigs for what can best be described as miniature white sea urchins: the eggs of the brown hairstreak butterfly.Each one is as tiny as you might expect, measuring just 0.6mm in diameter, and on a sunny day they can appear to sparkle in the light.

The eggs are designed to withstand the harshest of winter conditions and shelter the developing larvae within, which spend up to eight months inside their armoured shells.They are dormant for much of this time, surviving the winter in hibernation, but by late April the tiny caterpillars will be ready to eat their way out and begin feasting on the blackthorn's budding leaves.After a month or two of munching they will pupate and eventually complete their metamorphosis in late July, emerging as beautiful brown-winged adults, their undersides a spectacular orange patterned with delicate white lines.These are the last of the season's butterflies, winging their way into early October, and their numbers peak just as most other butterflies are dwindling.They are also the most elusive, flying high in the canopy or hidden within hedgerows, and adults are so rarely seen that egg hunts are the only reliable way to monitor the brown hairstreak's distribution.Sussex is one of the best counties in Britain for this nationally scarce species, and thanks to the concerted effort of a group of intrepid and dedicated egg-hunting volunteers we now have an accurate map of brown hairstreak distribution – and the good news is that its range seems to be expanding.The best place to see them in Sussex, if not the best place in England, is within the Steyning Downland Scheme area, where there is an annual brown hairstreak walk in August and females can often be observed egg-laying in September.

Brown hairstreak © Ryan Greaves

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