Wednesday, August 30, 2017

Magical roundabout

Durham County Council deserves great credit for the way it has planted roundabouts and road verges with colourful cornfield annuals.

This vibrant display is on the roundabout at the junction of the A68 and A689, just west of Crook. The rowan trees in the centre always produce a fine crop of berries but this year the addition of the flowers has produced a stunning display.

Corn marigold, cornflower, ox-eye daisy and corn poppy. A wonderful tapestry of colour.

Managing road verges in this way is a win-win-win strategy. It provides loads of nectar and pollen for insects, reduces maintenance, and makes a superb addition to the landscape.

This roundabout sits at the gateway to Weardale, part of the North Pennines Area of Outstanding Natural Beauty that is famous for its colourful meadows in summer. It provides a wonderful welcome to visitors to the dale. 

Tuesday, August 29, 2017

Painted Ladies

Lately a few painted lady butterflies have begun to appear in Teesdale and Weardale, wafted in by warm winds from the south. It's nothing like the spectacular invasion we enjoyed in 1996, when the first arrivals appeared in early July and bred on thistles to produce a second generation, so that there were enormous numbers by early autumn. Sometimes late invasions arrive in early autumn, as they did in 1903 (see below).

Painted ladies are noted for their infrequent but spectacular invasions and some of the largest of these, according to F.W. Frohawk in his Complete Book of British Butterflies published in 1934, coincided with wet summers in 1879 and 1903. 

This is how Frohawk described them:

"In 1879 the first migratory swarm appeared in North Africa in the middle of April. At Barcelona and Valencia enormous numbers occurred at the end of April and reached the island of Minorca on the first three days of May. On June 15th. vast swarms passed over Sevres, flying all day in a north-westerly direction. Similar flights were seen at Strasburg passing in countless numbers to the north, At Angers, on June 10th., an immense swarm flew over the city; it was estimated that between 40,000 and 50,000 passed along a single street in one hour; they were flying so low that pedestrians were inconvenienced by them. At Bisheim, on June 8th., the same phenomenon was observed and their numbers were so enormous that they darkened the sky. On June 11th. the flight that passed through Steyer in Austria, was so great that between one and two o'clock p.m. 90 to 100 per minute were counted in the breadth of 100 paces, the swarm being estimated at 1,000,000. Similar vast swarms were encountered in other places. 

Again, in 1903, a sudden and great invasion of these butterflies occurred in the autumn. They arrived in hundreds of thousands along the southern and eastern coast and dispersed over the whole of the British Islands. The flight was so vast that it extended from the Shetlands to the extreme south of England and Ireland. Their numbers were so prodigious that they swarmed along the whole of the eastern seaboard, from Durham to Kent, and wherever observations were made on the Scottish coast, they were abundant. The first arrivals of this vast invasion reached our shores on September 18th., and the flight continued for five or six days, their numbers increasing daily."

These butterflies look particularly attractive when you view them from below, with the sun shining through their wings that then resemble stained glass windows.

This individual was in Weardale yesterday, feeding on knapweed.

Thursday, August 3, 2017

Golden-ringed dragonfly

Dragonflies are the subject of my Guardian Country Diary today.

This is the peak period locally to watch these spectacular gold-ringed dragonflies Cordulegaster boltonii, which have the longest body (but not the greatest wing span) of any UK species. We discovered this female in the early morning, torpid after a cool night, resting on a patch of rushes next to a footpath.

There are several prime locations for this impressive insect here in the North Pennines. One of the best is in Hamsterley forest, near Spurleswood beck, which has the kind of crystal clear, highly oxygenated water and stony stream bed that forms a perfect breeding habitat. Another is along the river Derwent near Blanchland in Northumberland. A third is in Weardale, in a shallow stony beck that runs down the hill into the top of Tunstall reservoir near Wolsingham in Weardale.

While I was photographing this individual she began to warm up her flight muscles, first with just the merest hint of a vibration in her wings, until she was like a helicopter on the verge of take-off. Then she let go with those legs, which are of little use for walking but are used for gripping perches and catching prey in mid-air ..... and she was gone, hunting flies over the bracken.

The marvels of dragonfly vision are almost beyond our comprehension. We have trichromatic vision, with sensors that detect red, green and blue, which together define our visual spectrum. Dragonflies have sensors that detect at least five wavelengths, in addition to ultra-violet which is beyond our perception, and some species have thirty sensors that each detect a different wavelength, so their colour spectrum is vastly more complex and subtle than ours.

It's an interesting thought that those bright colours that we admire when we watch a dragonfly are not the colours that they see.

Then there are those massive compound eyes, each composed of thousands of separate facets (ommatidia), which give them highly sensitive flicker vision. When fast-moving objects cross their field of view they are tracked by a succession of ommatidia that convey the information to the brain.

Their amazing eyes, coupled with their speed of flight and extreme manoeuvrability, make them deadly aerial interceptors.