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16-05-2015

Baildon Moor – Green Hairstreak butterflies.

Very few birds and no butterflies were on the wing as I trudged up the hill from Baildon. Those birds which were in the air struggled to make headway.

5 people showed up at the top car park on Baildon Moor in the teeth of a fierce wind.

All of us agreed we were very unlikely to see green hairstreaks. 

Baildon Moor - looking towards top car-park from site of Green Hairstreak colony

I for one should have been more optimistic – In the previous two years the weather had been poor, but we had seen butterflies.

Despite our misgivings we started to search the patches of low bilberries and heather, just a few hundred metres from the car park.

I was at the edge of a shallow bell-pit when something brown fluttered at my feet, then vanished into the bilberries. Crouching to watch I was amazed to see a green hairstreak emerge and start feeding.

Just as the others arrived it flew off - but then butterfly after butterfly fluttered into view, all keeping close to the ground. They hung like emeralds from the bilberry flowers on which they were feeding.

Green Hairstreak butterfly on Bilberry

When we stood up we were buffeted by the wind, but getting low into shelter made a huge difference – the wind was gone, and the sun warmed us. There could be little better refuge. Doubtless this was what enabled this butterfly colony to thrive.

Next year I will show more optimism.

Notes

The Green Hairstreak is the commonest member of the Hairstreak family. It is the only adult UK butterfly which is green.

It is more common in the South and West. It is usually found, as with our butterflies, in a colony. The population of Green Hairstreaks appears to be getting smaller, presumably as a result of habitat loss.

Bilberry in Flower

One factor in its favour is that its caterpillars will eat a large array of plants – common foodstuffs include: gorse, birds-foot trefoil and bilberry. Its Latin name – Callophrys rubi - refers to a link with bramble as food-plant, rubi meaning “of bramble”.

Unlike the other Hairstreak butterflies which pass the winter as eggs, the Green Hairstreak overwinters as a pupa. The butterflies we saw had just emerged, and are on the wing as adults from late April until early July

.

Eggs hatch after about 2 weeks and caterpillars are ready to pupate by mid-August. Ants find the pupae attractive and may tend them. Some pupae have been found deep within ant nests. Pupae are known to “squeak" making a sound which is attractive to ants. 

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