Friday, August 31, 2012

Crisis Management



Even though they can ruin a picnic if you sit too close to an ants nest, I have great admiration for these industrious little insects. Look what happens, for example, when you accidentally disturb their nest; the first thing they do is grab the next generation and carry them to safety, while a few guard ants hang around to fight off any attacker. It all looks like chaos to begin with, but this is insect evolution's answer to crisis management.


Thursday, August 30, 2012

I Must Go Down to the Sea Again....


Today's Guardian Country Diary is an account of a little experiment in providing a new home for a hermit crab, which I've conducted many times before in aquarium tanks but not so often in a rock pool on the seashore.

Every now and then I get an irresistible urge to do a bit of rock-pooling on the seashore. Does anyone every grow out of the childhood compulsion to turn over a few rocks and see what lurks underneath? On this occasion we visited Whitburn Rocks, just north of Sunderland, on a lowish tide where the sea had retreated as far as the kelp beds - but I was so engrossed that I never got all the way down to the tide line, where the most interesting stuff lives, before the tide turned. 

This isn't the most biodiverse location but on this occasion the most striking feature was the sheer number of hermit crabs Pagurus bernhardus in the mid-shore rock pools. Even the smaller, shallower ones were home to dozens, sidling up to one another with their jerky, mechanical walk.




I supplied this one with this new, larger periwinkle shell to move into, which it immediately defended with this aggressive stance and menacing claw. Hermit crabs' growth is limited by the size of available empty gastropod shells and at Whitburn the vast majority of shells are periwinkles of similar size. Larger homes are hard to find. The ultimate prize - the hermit crab equivalent of winning the lottery and buying a mansion - is a whelk shell but they are rare on this part of the coast. 

Some of the most interesting research ever done on hermit crabs involved the use of replica glass shells, that the crabs would occupy and which allowed biologists to watch the intimate details of their lives inside the shell. Ian Lancaster, at Penwith Sixth Form College at Penzance in Cornwall used this technique and about 20 years ago he also published an excellent paper in Field Studies on hermit crab biology, which you can download free if you click here. You can watch a video of a hermit crab in a glass shell by clicking here.

Incidentally, if there's nothing else available hermit crabs will occupy homes made from Lego bricks - click here for video.




There were also plenty of chitons - primitive molluscs with eight articulated shell plates that give them the alternative name of coat-of-mail shells - like this one under the rocks, which I think is Leptochiton asellus. Their shell plates contain light-sensitive nerve endings called aesthetes, which are the earliest precursors of eyes and although that can't form images they can tell the chiton whether it's exposed on top of a rock or safe underneath it - invaluable information if there are hungry gulls about. I think it was Richard Dawkins who commented that, in relation to the evolution of eyes, 'half an eye is better than none'. The evolution of aesthetes in chiton shells was the first step in the evolution of mollusc eyes that culminated in the eyes of complex camera-type in squid, octopus and cuttlefish that are in some respects superior to those in humans. 

There are two other organisms in this picture: the keel worm Pomatoceros lamarcki, that has secreted its triangular-in-cross-section calcareous shell on one of the chiton's shell plates (click here for info for more seashore worms that live in tubes); and an acorn barnacle which looks like it might be Semibalanus balanoides.



The edges of these pools on the middle shore are fringed with forested of the red seaweed Corallina officinalis, whose gritty fronds are encrusted with calcium deposits, and it's in these swaying forests that much of the most interesting animal diversity lives - but much of it is microscopic. You can see some examples by clicking here, here and here



The sides of the pool were also home to beadlet anemones Actinia equina, ready to catch a paralyse prey with their stinging tentacles. If you poke their tentacles with your finger, thanks to the tiny, barbed nematocysts (also known as cnidocytes - for details click here) whose barbs catch in the surface layer of human sking but can't penetrate it, unlike the jellyfish nematocysts in this video that can.




I think these are the eggs of dog whelks and you can see from the ragged tops that most of the juveniles have chewed their way out, but the two in front seem to be intact.


There aren't many soft sediments for polychaete worms to burrow into on this part of the shore but there are several species that are flattened and live under rocks. I haven't identified this one yet but it looks like a scaleworm .


Aside from winkles and dog whelks, the most numerous gastropod molluscs are these grey top shells Gibbula cinerea, with their distinctive striped pattern. When that's abraded the underlying iridescent mother-of-pearl layer is exposed. 


..... and finally, a souvenir of the seashore to take home - the carapace of an edible crab Cancer pagurus.


Tuesday, August 28, 2012

No Hiding Place .....



When you cast a big shadow, there's nowhere to hide on a sunny day ....

Monday, August 27, 2012

Tempting trumpets ...




The pure white trumpets of hedge bindweed Calystegia sepium are a welcome sight in hedgerows or on urban waste ground in late summer, but it's certainly not a plant you'd want to introduce into a garden, where it will curl around and strangle anything it can reach. It has invaded our garden and its white, brittle, deeply buried rhizomes have proved just about impossible to eradicate. They regenerate from the smallest fragment. 




...... but if I didn't know better I might almost be tempted to cultivate this pink-striped form. 


I know of a couple of places where this grows wild, on the edge of a reed bed near Alnmouth and in a hedge near Sunderland Bridge just outside Durham, so given its invasive tendencies I'll just visit and admire it occasionally, rather than grow it.

Friday, August 24, 2012

The End of the Pier Show...

Roker pier and lighthouse, at the mouth of the river Wear in Sunderland. A fine place for a stroll on a summer's afternoon like today, with bright sunshine, barely a breath of wind and almost a flat calm sea at low tide. 


A good place to watch seabirds too, like this juvenile cormorant ....


......learning the art of diving for fish. The trick is to push down hard on the water surface with that broad tail, to give the dive a bit of momentum ...


.... and at the third attempt it caught this. It seemed surprised and not quite sure what to do with such a large and lively catch, which looks like it might be a an eel-pout .........


.... which are notoriously slimy ... which may be why the bird struggled with its grip, dropping and re-catching its prey twice ...


.... before it managed to get the fish's head into its throat and started to swallow it ....



.... which didn't go according to plan. The fish must have been putting up a fight inside the bird's throat because the cormorant regurgitated it ...


.... dunked it in the sea a few more times, then swallowed it again ...


 ....and this time the catch stayed down. Must be still wriggling though, judging from that thoughtful expression on the cormorant's face.



No such problems for the terns which fished alongside the pier.


The calm, sunlit water was remarkably clear, so you could see vast shoals of small fish swimming in unison above the sandy bottom. There must have been well over a 1000 in this shoal but the terns ignored them, even through they flew over them many times ..... maybe they were too small to merit a plunge-dive ....























.... or maybe they preferred to catch their fish in deeper water...



Meanwhile, alongside the pier this year's guillemot juveniles were relentlessly pursuing their parents ....


....... adopting a submissive posture .......


.... and calling incessantly for food .....


..... which must have been easy to spot by peering down into the sunlit water like this.....























...... and the water was so clear that I could watch the birds 'flying' underwater in pursuit of prey.


Thursday, August 23, 2012

A Blue Scarlet Pimpernel





Nearly forty years ago, when I worked in the Agricultural Research Service, I visited a farm in Shropshire where I noticed the blue form of scarlet pimpernel Anagallis arvensis ssp. foemina growing in a field of onions, alongside the typical scarlet form. This beautiful blue variant is rather uncommon and restricted to central and southern England, so I never encountered it again when I moved to north-east England - until now. Last year I was given some seeds of A. arvensis ssp. foemina and this year they've flowered in our garden. The gentian-blue flowers are as exquisite as I remember them from that first encounter.



The scarlet form already grows in our garden. The plant is also known as poor-man's-weather-glass as the flowers close quickly when the sun is obscured by cloud - so they've been closed rather a lot this summer. They also close entirely in mid-afternoon every day, as regular as clockwork.

The other curious feature of these plants is their spherical seed capsule, known botanically as a pixidium, that opens by splitting around its circumference - click here to see one in action.

Wednesday, August 22, 2012

Something rotten...


After so much mild, wet weather this summer it promises to be a good autumn for toadstools. I found this fungal mycelium, composed of bundles of microscopically small fungal hyphae, growing over the surface of decaying pine bark mulch in our garden. Ultimately they'll digest food that lies in their path, multiply, unite and organise themselves into a toadstool, the fungal fruiting body that produces spores, but exactly how this transformation is organised remains one of nature's mysteries. 

There's more on the microscopic structure of toadstools here


Tuesday, August 21, 2012

Ichneumon wasp




Earlier this week we found this menacing-looking wasp high up in the Pennine moorlands near Alston in Cumbria. I wasn't too certain of its identity and thought it might be a digger wasp, but thanks to the kindness of Africa Gomez (check out her BugBlog site, it's excellent) I now know that it's a large ichneumon called Amblyteles armatorius, which lays its eggs on moth larvae, which the grubs then feed on.  Gruesome. Magnificent antennae, though. 

Apparently it usually spends most of its time on hogweed umbels and some sources say that it's a lowland species, so the fact that it was grounded and living at high altitude led me astray with the ID.

You can find more information on this insect by clicking here and here 

Friday, August 17, 2012

...... and now for the good news.....


If you let it, taking an interest in natural history could be very depressing because so much that is written about our flora and fauna in the press seems to be unrelenting bad news. The abysmal weather in the early part of this summer  produced also sorts of hyperbolic headlines of the disastrous/cataclysmic/catastrophic kind about its likely impact on birds/butterflies/insects and almost everything else in the natural world - and it's undoubtedly true that it has been a bad summer for all of these (although it's important to bear in mind that over last few thousand years there have been periods of far more adverse climatic conditions that our wildlife experienced and rebounded from: like investments, rates of growth in populations of living organisms can go down as well as up, all the time). The natural world isn't a natural history museum, it's a living, constantly evolving interplay between organisms.

Anyway, last weekend we happened to notice a positive effect of the wet early part of the summer, when we took a walk along the cliff tops between Dawdon and Hawthorn Dene on the Durham Coast Heritage Path. The summer wild flowers there seem to be flowering more spectacularly than I can ever remember. I have a theory as to why this might be so, and it's all down to the rain. 

The cliffs are porous magnesian limestone which is free-draining. In a 'normal' summer the surface soil dries out quickly and the plants suffer from moisture stress, so they flower quickly while they have the chance, when they are quite small. This year, with plenty of water, the well-watered vegetation is unusually lush and as a result the flowers are truly spectacular. So, without further ado, here are some examples....


Drifts of meadowsweet in the gullies on the cliffs and ....


.... forming a backdrop for devil's bit scabious which .....


...... includes some exceptionally fine examples ..... although this one looks a tad unusual - very short bracts under the inflorescence and it looks like it might be male-sterile, judging by the tiny stamens.


... along with field scabious .....



... flowering in profusion in the meadows at the end of Hawthorn Dene ...



... where there are some fine specimens of giant bellflower.



































I suspect that alkaline soil might be the reason for the very blue hue of the tufted vetch on the cliffs but .... 



... this unusually pale betony plant (normal flower behind) is probably a genetic mutation.



Bloody crane'sbill always puts on a good show ....























.... and this year centaury has done well too, with some very floriferous plants ...


This is hemp agrimony .....a major constituent of the taller vegetation while .....



































.... hoary plantain is blooming down amongst the grasses.


Plenty of knapweed Centaurea nigra, alongside the ....




.... greater knapweed Centaurea scabiosa.



Drifts of marjoram aka oregano (crush the leaves and sniff for a tantalising hint of Mediterranean cuisine!)....


Spear thistle already running to seed ....



































.... likewise agrimony, producing its little bell-shaped hooked fruits ....



Yellow loosestrife ....



































.... and some wonderfully robust specimens of yellow-wort, with its strange glaucous, stalkless leaves.
























In dry summers yellow-wort, which is an annual, is often a stunted plant and only produces a few flowers - but this year some plants have responded to the rain with a wonderful display...


... and the North Sea provides a fine backdrop for the floral spectacle ....



..... and for haymaking ....