Mid-winter Pond Dipping

Thursday's Guardian Country Diary is about freshwater invertebrates that remain active all through the winter. There may be no bees or butterflies about at the moment, but there are plenty of aquatic animals to look at - the only problem is that the water is bone-numbingly cold, so collecting them can be a bit of an ordeal! 

All the animals below (except the bottom one) were found in a single jam jar of water, dredged along the edge of our garden pond which had been frozen over on the previous night.

This is a freshwater orb-cockle Sphaerium sp. There must the hundreds of these little bivalves (the largest was about 8mm. across) in our pond. The two pink protruding tubes on the left are the inhalent and exhalent siphons that circulate water over the gills. You can just see the muscular foot protruding through the shell valves in the 5 o'clock position. 

Orb-cockles are surprisingly mobile, especially when they are small. This one, whcih was about 4mm. long, is using its muscular foot (which you can see protruding from the back of the shells) to scoot across the bottom of the container.

There are scores of these red ramshorn snails in our pond but it's providing difficult to identify it precisely. I posted the pictures on the excellent iSpot web site and there are varying opinions as to its identify. It might be Planorbis corneus rubrum or it could be Planorbella duryi which is the American ramshorn snail. Either way it's an introduced species that probably came in with pond weed bought from a garden centre.

If there are scores of ramshorn snails, then there must be many thousands of these flatworms (Polycelis nigra?) in our garden pond - there were over 50 in a single jam jar sample. They glide along like magic carpets, propelled by a covering of beating cilia which you can see on a marine species by clicking here.

Our pond has a thick layer of decomposing leaves at the bottom - perfect conditions for water slaters (aka water hog-lice), so there are large numbers present.

Gammarid shrimps like these prefer well oxygenated flowing water so our somewhat stagnant pond is far from ideal, but there are still plenty present in the shallows and they are very active swimmers, making them difficult to photograph.  Mostly they swim on their sides, or sometimes upside down, curling up when they are alarmed. These have an interesting history - I introduced them from a population that I rescued from the bottom of Wearmouth Colliery before it closed; you can read the details here.

The young gammarids are almost transparent - I think this must be a male, judging from those prominent claws on the front pair of legs.

And finally, this animal (below) is not from our pond. I collected it a few days ago from the gravelly bottom of a ditch, with snow melt water flowing over it, on the edge of the moors at St. John's near Wolsingham in Weardale, and it's ........

...... an exquisite little caddisfly larva, with a tube constructed mostly from quartz grit. They can be coaxed to build their tubes from more exotic materials - for a stunning example, click here

A Black Caddis fly

We paid a short visit to Edinburgh this week and while we were there spotted this unusual black caddis on a bridge parapet at Stockbridge, over the Water of Leith. I think it is probably the longhorn caddis, Mystacides nigra.

It was smartly turned out in black livery (with just a hint of blue iridescence) and with eyes like garnets, but the most eyecatching features were those long white antennae - not just because of their size.....

.... but because of the way in which it waved them around, alternately waving each backwards then forwards.

Caddis flies, which belong to the insect order Trichoptera, are remarkable, both in the aquatic stage of their life cycle when most live inside tubes that they make from plant material or small stones, and when they are adults. You can see another example by clicking here and can read more about their biology here and here.

Newly-hatched caddis fly

I was sorting through some pondweed yesterday when I found this caddis larva. I don't know what the species is but I think it's one that lives between waterlogged dead leaves, rather than one that constructs a distinct tube to live in.

I could see that it was just about to hatch - you can see the well-formed wings in this picture.

A little later, when I looked again, the imago had hatched and climbed out on top of the waterweed. It's still drying its wings here and you can see the shed larval skin, down in the bottom right-hand corner of this photo. The caddis fly is still grooming one of its antennae.

Here's a the shed skin a little closer - I wish I'd been around to see the imago slide its long antennae out of their larval skin.

Still conducting pre-flight checks here.

One newly-minted caddis fly, ready to take to the skies.

If you've never seen it, it's well worth checking out this web site and this video, to see some amazing bejewelled caddis fly larvae.

A Trawling Caddis fly, a Hot Climb and a Railway Revival

This is Philopotamus montanus, aka the dark-spotted sedge, a caddis fly that we found on this morning's walk along Shittlehope burn, that flows down from the moorland above Stanhope in Weardale to the river Wear in the valley bottom. Most caddis fly larva live in a tube that they construct from plant material or grit, but this beautiful little caddis has an even more remarkable life cycle. The larva spends its formative years below waterfalls, where it spins a silken net that resembles a trawl net, attached to a rock with the mouth facing upstream, filtering out food particles that the current delivers.

The adult, more or a flutterer than an accomplished flier, is beautifully camouflaged against the dead leaves that still persist along the edge of the burn at this time of year.

And here's the dark-spotted sedge's preferred habitat, one of the many small waterfalls that punctuate Shittlehope burn's route to the river. The burn has carved out a steep-sided gorge whose banks are currently dominated by wild garlic, but other elements of the flora here include primroses, violets and globe flower - although it's a few years now since I've seen the latter here; it's much less often seen in Weardale than it is in Teesdale, the next dale south from here.

This is the middle section of the burn, before it cascades downhill. By the time we reached here we were pretty breathless - I'd forgotten what it was like to be too hot when out walking and today's soaring temperatures had us labouring a little as we headed uphill, but it was worth it because we reached the high pastures just in time to see...

... the 10.45am from Wolsingham chuffing into Stanhope station.

After a bit of a financial struggle the Weardale Railway is running regular steam-hauled services at weekends and the sight and sound of a steam train puffing up the dale marks the welcome return of a branch of the rural rail network that many believed had vanished for ever...