Azure butterfly bounces back from cyclical decline caused by parasitic wasps with numbers increasing by 151% on last years’ annual Big Butterfly count
Monday 12 October 2015 06.01 BSTLast modified on Monday 12 October 201506.03 BST
A butterfly locked in a cyclical struggle with a parasitic wasp has bounced back this summer after years of scarcity, according to the world’s largest annual insect count.
The holly blue, the only blue butterfly regularly seen flying in gardens and city centres, increased by 151% on 2014 in Butterfly Conservation’s Big Butterfly Count.
It was a welcome return for the azure insect, whose populations boom every six years or so due to its relationship with a parasitic wasp, Listrodomus nycthemerus. The wasp injects a single egg into the living Holly Blue caterpillar via a syringe-like sting. The wasp larva develops within the caterpillar, eventually killing it after it has changed into a chrysalis.
The parasite is completely dependant on the holly blue and can be almost too successful – killing all 100 caterpillars monitored in some scientific studies. Once holly blue numbers have been drastically reduced, the wasp’s population crashes as well.
This allows the butterfly to recover again – holly blues previously boomed in 1976, 1984, 1990, 1996 and more recently in 2010.
This year, the butterflies were seen in St James’ Park and Battersea Park in central London and as far north as Edinburgh.
Despite an often miserable July and August, a record 52,204 people took part in the count this year, spotting almost 600,000 butterflies.
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