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.

Saturday, July 29, 2017

Some early Amanita toadstools - another symptom of a warmer world?

It seems strange to be blogging about toadstools like these in July ....... I can't recall seeing either of these in Weardale quite this early in the year. Both were photographed yesterday in Backstone Bank wood near Wolsingham in Weardale. There were also numerous larch boletes Suillus grevillei in the larch plantation and some slippery Jacks Suillus luteus amongst the Scots pines, mostly eaten by slugs.

Grey-spotted amanita 
Amanita spissa

Fly agaric 
Amanita muscaria

There is now quite a substantial body of evidence that fungi are fruiting earlier as a result of climate change, and in some cases fruiting in spring and autumn. Various reasons have been suggested, including one that mycorrhizal fungi like these (which form a symbiotic link with tree roots) are receiving more nutrients from the trees that now have a longer growing season. Another is that decay rates in forest soils are increasing as average temperatures rise.

A major survey at Cardiff university in 2007 revealed that some species are fruiting for much longer, with an increase in some species from 33 days in the 1950s to over 75 days.

Maybe summer fungal forays will become commonplace in future.

You can read more scientific research about the links between climate change and fungal fruiting times by clicking here and here and here and here

Sunday, July 23, 2017

Moss pop-guns

It's not very often that I find bog moss (Sphagnum) bearing spore capsules. They are easy to overlook because they are not raised on a long stalk (seta) like the capsules of many other British mosses.

I found these on cushions of Sphagnum growing in a little hillside mire near Wolsingham in Weardale. I'm wondering whether it may have been the very dry spring followed by wet mild weather that triggered rapid growth and their formation.

The capsules remind me of small, round ginger jars.

They are unusual because, unlike most moss capsules that shake spores out through pores or peristome teeth, these literally explode.

As the capsules mature they lose water and the air inside them becomes pressurised. As the walls contract the capsules change shape, from spherical to cylindrical like the rearmost in this photograph. Eventually the lid blows off, sending a mushroom cloud of thousands of microscopic spores, in a vortex like a smoke ring, about ten centimetres into the airstream.

You can watch a high-speed film of the whole process by clicking here and here