Sunday, May 30, 2010

Climbing the Walls

If you have an oldish house with some dark, damp corners - like ours - the chances are that you'll discover sooner or later that you are sharing it with daddy-long-legs spiders Pholcus phalanioides. This is a spider that is only found inside buildings in Britain. It comes from warmer climates and can't survive outside here.

I spotted this individual climbing the walls of our stair well at around midnight last night and noticed that it was carry something in its jaws.

Its cargo turned out to be its eggs, that looked like they might be close to hatching, which female Pholcus spiders carry around for safety. Even an arachnophobe would have to admire this high degree of maternal care. After dark, when we humans sleep, spiders emerge from behind bookcases, under settees and from inaccessible corners to conduct their nocturnal lives, and this one seemed to be moving home, perhaps to spin one of its untidy webs in a corner where it will catch enough prey to feed its spiderlings. If it doesn't, they'll eat each other. Pholcus is especially partial to catching and eating other spiders, including its own kind.

For more on the intriguing world of spiders take a look at the British Arachnological Society web site at

Saturday, May 29, 2010


Saxifrages tend to be associated with mountains - after all their Latin name refers to their habit in growing in rocky crevices - but this species, meadow saxifrage Saxifraga granulata, thrives in grass. It's a declining wild flower but it still has some strongholds up here in North East England, in Teesdale in particular.

Meadow saxifrage has its own distinctive technique for growing and flowering before being shaded out by other vegetation. If it just reproduced from seed it would struggle to compete with grasses but at the end of flowing dozens of tiny buds called bulbils (the 'granules' of granulata), form at the junction of the leaves and stem and when the rest of the plant withers away these sit on the soil surface over the winter. When spring comes they sprout leaves and flowers quickly, stealing a march on the grasses. The flowers still produce large numbers of tiny, widely dispersed seeds and for this they need pollinators, but this particular flower was a potential death trap for an unwary hoverfly visitor.....

... with a spider lurking under the petals, waiting to ambush visitors.

Friday, May 28, 2010

Ermine and Silk

Bird cherry Prunus padus has a predominantly northern distribution in Britain and it's a prominent feature of hedgerows in Co.Durham in late May.....

...... when it is often smothered in long racemes of flowers. This specimen was photographed ina  hedgerow at Wolsingham in Weardale.

But, just when flowering is at its peak ....

...silken tents begin to appear on the fresh young leaves. These are woven by small ermine moth caterpillars .....

... that create a communal protective tent within which they can safely feed. Other species of ermine moth infest hawthorns and spindle trees. Occasionally trees are so heavily infested that they can be completely defoliated and wrapped in a silken sheath....... producing a spectacle that sometimes attracts the attention of the national press.

Wednesday, May 26, 2010

Tales from the Riverbank....

Many of the rocks along the banks of the upper reaches of the river Wear carry the empty nymphal cases of stoneflies, recognisable by the paired tail filaments. The split in the thoracic segments marks the point where the adult insect eased its way out of the nymphal exoskeleton after the nymph crawled out of the water.

Stoneflies tend to be confined to fast-flowing, well oxygenated, unpolluted rivers, which is a pretty good description of this stretch of the river Wear between Wolsingham and Black Banks, in Weardale. Currently, after a long spell without heavy rain, the water level is low and mayflies are laying eggs in the shallows and pools.

Mayflies are the only insects that moult in their adult stages. The winged adult that emerges from the nymph is the subimago (known to anglers as a 'dun') and this undergoes a final moult to become the imago ('spinner' in angling parlance). This is an imago that appears to be laying eggs, and drowning in the process. Females have shorter front legs than the males.

Mayfly nymphs have three tail filaments but the adults can have two or three tail filaments, depending on genus. The hind wings in mayflies are much shorter than the forewings....

.. and both pairs are held vertically above the body when at rest.

There are two large compound eyes and three small ocelli in between them. Adult mayflies do not feed during their short lives, so there are no functional mouthparts.

Male mayflies are notable for their extremely long front pair of legs, which are used to grasping females during mating flights.

During emergence and mating flights low over the water surface, vast numbers fall victim to fish - especially leaping trout - while those that survive fish predation ...

....become food for birds like dippers, which also feed on the nymphal stages of stoneflies and mayflies.

Tuesday, May 25, 2010

Life and Death Struggle....

We encountered this life-and-death struggle between a ground beetle larva and an earthworm that had ventured out of its burrow in Teesdale.

The beetle sunk its jaws into its victim and refused to let go, even though...

... the worm twisted and turned...

... rolled over on its attacker.....

... and glued it down with sticky mucus.

We didn't watch the end of the contest. I suspect the worm might have reached safety, though some segments may have been severely damaged.

More examples of mortal combat:

Saturday, May 22, 2010

To the Woods.....

The bluebells in Durham's woodlands are just about at their best now, with the leaf canopy overhead allowing shafts of sunlight to sweep across the mist of blue flowers on the woodland floor. This is a woodmouse-eye-view. In the hot, still humid air the whole of this woodland, just outside Durham city, smelled like a florist's shop....

... but with a few more days of this heat the bluebells will soon begin to fade.

This breathtaking annual display of bluebells has its origins in the previous year's summer. As the flowers fade the plants use the brief window of opportunity before the leaf canopy closes overhead to build up food resreves in a new bulb, where next year's flower initials will already be formed by mid summer. By late summer the leaves will have wilted, leaving only the papery seed heads, while underground next years bulb, primed and ready to go, will sit out the winter ready to burst into life when spring returns. 

Meanwhile, down amongst the bluebells the spreading fronds of buckler fern Dryopteris sp. have already expanded. The whole plant is a living waste-paper basket, catching leaves in that funnel of foliage in autumn and trapping them around the crown of the plant, where they'll decay and create humus around its roots.

Tuesday, May 18, 2010

One-Sided Relationship

Dandelions are a terrific source of nectar and pollen for bumblebees ...

.... and for small solitary bees like those above. Can anyone help me identify any of these?

It might seem that this is a perfect example of a partnership between plant and pollinator, with generous rewards for services rendered by the insects, but this is a very one-sided relationship. Unlike typical flowers, most dandelions don’t actually need any pollen to set seeds.

Seeds are usually produced when male pollen fertilises a female egg cell inside the flower to produce an embryo inside of the developing seed, but in many dandelion species seeds are produced without the need for fertilisation, so the seedlings are genetic clones of the mother plant. All that pollen and nectar that sustains the bees, as well as the elaborate mechanism for presenting pollen to bees to maximise the chances of cross pollination, is redundant as far as the dandelion is concerned - a needless expense.

This production of seeds without pollination is called apomixis and in recent years it has attracted the interest of genetic engineers, because if it could be enginerred into GM crops they wouldn't require pollen for seed production. This would remove one major objection to these high-tech crops – that they can transfer their genes via pollen to organic crops or wild plant relatives. Without pollen, an apomictic crop could not contaminate non-GM crops, with the added bonus that it could reliably produce seeds without depending on insect pollinators.

Monday, May 17, 2010

Hawthorn Hive

The landslips on the beach at Hawthorn Hive on the Durham coast (above) have a fascinating limestone flora, where the shelter of the cliffs often coaxes plants into flower early.

Last weekend we found the first bloody crane'sbill flowers opening ...


... at the same time as the last of the dog violets were beginning to fade ....

..... while common milkwort was also just coming into bloom


... and glaucous sedge was also flowering. The upper flower spike on the sedge carries the stamens that have already shed their pollen, while the lower two flanking it are female, identifiable by the feathery white stigmas protruding from them. Sedges are easily identifiable by the triangular cross section of their stem - roll the stem between finger and thumb and you can feel that it's three-sided.

Meanwhile, twayblade orchid flower buds are still developing, and it will be a week or two yet before they open.

Sunday, May 16, 2010

Life on the Edge

The Durham coast used to be famed for industrial dereliction and coal waste dumping, but thanks to a wonderfully successful clean-up campaign it's now a great place for coastal walking, where you can get eye-to-eye with a kestrel as it glides on the updraft from the beach.

The cliffs south of Seaham are becoming popular with birders  - it's a great place to watch the fulmars that nest on the cliffs as they glide by .... 

... and yesterday the scrub on the cliff top was alive with singing whitethroats

... along with this smartly turned-out cock chaffinch..

The calcareous grassland along the Durham Coastal path is now part of the Durham Heritage Coast and just now the cowslips are coming into full bloom ...

.... along with the early purple orchids - a narrow strip of floral diversity, perched on top of the crumbling cliff edge

Friday, May 14, 2010

Mollusc Hoodie

Most specimens of the large black slug Arion ater are jet black, but I found this handsome red form with grey tentacles crawling across a woodland path near Durham city today. The red form is much commoner in the south of England. In the image above you can see the large open breathing pore (pneumostome) that leads to the mantle cavity - a simple form of lung.

The whole slug was covered in a layer of grey mucus and ....

.... when fully extended was about 12 cm. long. This is our largest slug species.

Arion ater has very distinctive behaviour when you give it a prod. First it withdraws its tentacles under a hood and closes its pneumostome, then it gently rocks from side to side, as if in silent fury. This behaviour, combined with that distasteful mucus, probably deters a lot of predators.

After a while it will begin to extend an inquiring tentacle from under the hood, to see if the threat has gone and the coast is clear ...

.... and if it is it extends its tentacles, opens its pneumostome (to breathe a sigh of relief?) and glides away into the undergrowth.