Friday, August 30, 2013

Botanical artillery...

Cranesbills are wild flowers with a particularly violent method of dispersing their seeds, that involves a catapult mechanism and is particularly well developed in bloody cranesbill Geranium sanguineum.

Cranesbills belong to the genus Geranium, a name that's derived from the Greek word geranos, meaning 'crane' (the bird, not the mechanical device) and nicely describes the central axis of the fruit, which resembles a crane's beak.

There are five egg shaped seed containers at the base of that long beak, which is formed from five long strips of plant tissue that are firmly attached to the tip of the beak and develop tremendous internal tensions as they dry out. They are botanical springs and when their inner tensions reach a critical point they break free at the base and curl away from it with enormous force......

.... so that they curl upwards with the egg-shaped containers attached, hurling out the seed which lies in each container, in much the same way as those dog ball throwers that dog walkers use. After the seeds have been dispersed this elegant candelabra-like structure is left behind.

Bloody cranesbill is the official county wild flower of Northumberland.

Wednesday, August 28, 2013


Thursday's Guardian Country Diary describes the mosquitoes that breed in almost every small accumulation of rain water in our garden. The sultry wet weather that we've experienced lately has provided perfect breeding conditions for the larval stages and I've been watching their development.

These are the larvae, hanging from the water surface by their tail breathing siphons. Those jaws are less menacing than they look - the mouth is fringed with small whiskers that constantly move, creating a water current and filtering out food particles. The larvae of this species, Culex pipiens, moult four times as they grow and you can see two developmental stages in the photo above - the larger larvae are at their final stage of development and are ready to become .....

....... pupae. You can see a comma-shaped pupa floating amongst this gang of larvae.

The pupae hang from the surface with two breathing tubes on the head that resemble devilish little horns.

The pupal stage is relatively brief and as the mosquito develops inside and they move closer to hatching they become darker, like the one on the right. The larvae are very active, wriggling down to the bottom of the water at the slightest disturbance, but the pupae are positively hyperactive if you disturb them, tumbling as they dive. 

When they are ready to hatch the pupae float passively on the surface and their tails straighten, like the one at back that you can see here. Then ....................

Their exoskeleton splits along the back and a mosquito's head and antennae appear above the surface.

Some don't make the successful transition from water to air if they are disturbed during this critical step - the one on the left has become trapped in the surface tension and has drowned; you can see the empty pupal skin floating below it. 

The photographs below show several more stages in a successful emergence. Adult mosquitoes look menacing from the moment they appear above the surface, don't they, with those intricate, ultra-sensitive feathery antennae and suctorial mouthparts? They have their own brand of sinister beauty - you can see view some images of their rather beautiful eyes by clicking here.

The sequence of  six photographs below show another successful emergence. 

It's only in the third photograph that the legs begin to play a part; before that the insect just wriggles out of the pupal skin, perhaps aided by those backwards-curved hairs. The strange discontinuity that you can see bisecting the mosquito here is an optical artefact, caused by the water meniscus on the side of the glass container.

Once the insect's legs are free it can rest them on the surface film and finally lever its abdomen out of the pupal skin, until ...........

..........finally it's free. 

The species in these photographs is Culex pipiens. It spends autumn feeding of plant juices and the mated  females that survive the winter will need a blood meal before they can lay eggs and produce the next generation in summer 2014. Fortunately this species feeds on the blood of birds rather than humans.

Many will not survive the autumn; thousands become trapped in spiders' webs. They are also important food items for birds like swallows and house martins and the pipistrelle bats that hunt over our garden will probably catch them in large numbers too.

Tuesday, August 27, 2013

Mirid bugs...

These little mirid bugs are extremely common on plants during the summer - especially on umbellifers - and there are numerous species. Fortunately the excellent British Bugs web site provides an excellent photographic guide that covers many of them.

This species is the very common Grypocoris stysi, which is often found on umbellifer flower heads, like the hogweed below.

I think this little green species, which turns up on many plants in our garden, is possibly the common green capsid Lygocoris pabulinus, but there are several rather similar small green capsid bugs so I could be wrong.

You can see the typical capsid proboscis here, which can penetrate plant tissues, the bodies of small insects and even human skin in some of the larger bug species, like water boatmen.

I thought this species, which took up residence on the dill plants in our garden, would be easy to identify because of that yellow chevron marking - but there are several similar species that are described as 'very variable' in their markings, so Liocoris tripustulatus is not much more than a guess at an identification.

You can find a picture of a more colourful species by clicking here.

Monday, August 26, 2013

Reason to be cheerful....

Less than a decade ago, seeing a speckled wood butterfly in Durham or Northumberland would have been something to get excited about; then they were rare vagrants. Now they can only be described as common - we must have seen more than twenty when we walked along the south bank of the river Tyne between Wylam and Newburn yesterday, and today there were several in our garden in south west Durham. Now you can expect to see them almost anywhere along woodland edges and in sunlit glades. The rapid expansion of their range has to be one of the wildlife success stories of the last decade.

Saturday, August 24, 2013

Right time, right place, wrong gear ...

A recent photograph on Flickr by Bob the Bolder showed a salmon leaping the wear on the River Wear just below Durham cathedral in mid-August, which is early for these fish to start moving up river to spawn. 

One October afternoon five years ago I happened to be walking past Spurleswood beck in Hamsterley forest in Weardale just at the time when salmon were trying to leap the waterfall there. We watched for half an hour while fish after fish hurled itself into the torrent but none made it to the top. Conditions were probably close to perfect for the fish, with the beck in spate and a deep plunge pool below the waterfall where the upwelling water would have given the fish extra impetus, so maybe some made it after we left. 

It's hard to be sure whether these were sea trout or salmon but judging from the indentation in the tail fin I think they were salmon. Sea trout tend to have a straight trailing edge to the tail fin.

I didn't have any decent photographic gear with me when I took these bu,t judging by Bob the Bolder's photo, now is the time to plan for a return visit............

Wednesday, August 21, 2013

When Jurassic harvestmen walked the earth.

The raspberry bushes in our garden seem to be a favourite haunt of harvestman, including this one which I think is a male Leiobunum rotundatum. They're often there early in the morning, when they drink dew on the leaves, but later in the day I suspect that they come to drink the juice leaking from damaged fruit.

Fossils from the Rhynie chert in Scotland show that harvestmen have existed for at least 400 million years, more or less unchanged, and you can download a scientific paper with pictures of an exquisite 165 million year old Jurassic harvestman fossil by clicking here.

Since these animals first evolved there have been five great, catastrophic mass extinction events that wiped our many life forms, including the dinosaurs; amazing, isn't it, that these lanky, fragile animals that will shed legs if you touch them have survived while the dinosaurs didn't............

You can find more information about these intriguing animals by clicking here and some more pictures of harvestmen by clicking here

Tuesday, August 20, 2013

Life in the undergrowth .....

Some insects in our garden undergrowth (it's a jungle out there!)

An anxious cabbage white butterfly, checking that the coast is clear. Beautiful eyes.

A marmalade hoverfly Episyrphus balteatus, hanging in the air in a sun fleck.

Amazing eyes of a much larger hoverfly Volucella pellucens , feeding on some leeks that we never ate and have now flowered - the big, spherical flower heads are very popular with bees and hoverflies. 

Volucella pellucens is a hoverfly that breeds inside wasp nests........ 

........... and might even have laid eggs in the nest of this wasp, that was hunting for small insects on dill umbels.

This froghopper was on the same umbel as the wasp but well beyond its reach, tucked in amongst the 'spokes' of the dill's umbrella-shaped inflorescence.

Monday, August 19, 2013

A plant with 100 names

Until a few years ago we had just one plant of cuckoo pint Arum maculatum in our garden but every year more appear - probably because the blackbirds are eating the ripe fruits and dispersing their seeds. I reached this one before the blackbirds found it.  It's well known that cuckoo pint berries are dangerously poisonous to humans but birds seem immune to its toxins, as they are to those of many other poisonous plants, including deadly nightshade.

Cuckoo pint is a fascinating plant in many ways. Most of the aroid family, to which it belongs, are native to warmer climates and include the spectacular titan arum and the voodoo lily, whose stench is breathtakingly awful . Almost all aroids have fascinating pollination mechanisms and cuckoo pint is no exception, trapping small insects such as owl midges in its inflorescence until they pollinate the flowers - you can find photos and an explanation by clicking  here.

Cuckoo pint is just one of over a hundred regional vernacular names for this plant, which is unusual in being a rare example of a single species in the British flora that has had a whole book devoted to it, under one of its aliases - Lords and Ladies by Cecil T. Prime, published in 1960 as a special volume in the Collins New Naturalist series. It's well worth seeking out a copy of this scholarly but highly readable book, in which Prime describes every aspect of the plant's biology and history, including its use in the production of starch for stiffening the extravagant  ruffs worn by Elizabethan courtiers. During this period starch was produced from cuckoo pint's tubers when starch from wheat was in short supply.

Later the industry was relived on the Isle of Portland in southern England and Prime describes the hazards of the laborious extraction process, quoting John Gerard: "The most pure and white starch is made of the roots of Cuckow-pint; but most hurtful to the hands of the Laundresses that hath the handling of it, for it choppeth, blistereth, and maketh hands rough and ragged and withall smarting"

The hurt was caused by needle-sharp crystals of calcium oxalate which are present in high concentrations in the tubers and in other parts of the plant - you can see photographs of similar crystals in another plant by clicking here.

It must have been incredibly laborious work - last year I dug up a cuckoo pint tuber from the garden and found that it was about the size of an acorn; vast numbers would need to be harvested to produce starch in commercial quantities. Remarkably, the industry continued in Italy (in Tuscany) using the closely related Arum italicum right up until 1919.

Sunday, August 18, 2013

An immaculate summer bolete

We found this very fine toadstool, which I think is the summer bolete Boletus reticulatus, near a poplar on the grass verge near Van Mildert college in Durham city today. Remarkably, although it's a mature specimen it appears to be completely unscathed by slugs, which often feed on toadstools well before they reach this stage of maturity.

Field guides describe the way the top of the cap of the summer bolete breaks up into scales as it expands - exactly as this specimen is doing. 

The summer bolete tends to be the first Boletus species to appear each year - perhaps it's a sign that this will be a good autumn for fungal forays............

Saturday, August 17, 2013

Sycamore Aphids

Recently there has been a lively exchange of comments in the Guardian on a piece by George Monbiot that extols the virtues of native trees because they support insect biodiversity (birch hosts no less that 266 different invertebrates, for example) and deplores the tendency of local authorities to plant non-native trees that are of relatively little value to our native fauna.

One of the most frequently cited examples of a non-native tree with a very limited insect fauna is sycamore, which hosts a paltry 15 species. It's a long-established non-native species with a  documented history here that dates back to the 16th. century, but since then only a small number of our insects have adapted to it. But what it lacks in biodiversity, it certainly makes up for in the sheer quantity of one particular insect that lives on its leaves - the sycamore aphid.

Over the summer these little insects multiply in vast numbers under its leaves - and they produce a lot of honeydew, so woe betide anyone who parks a car under the tree; it will be as sticky as a toffee apple if it's left there for long. 

The positive aspect of this sticky secretion is that the mildew that grows on the sap that the aphids excrete is an important food source for the orange ladybird Halyzia sedecimguttata, whose distribution is linked to that of sycamore.

All these aphids are certainly of real value to some of our native birds - I've often watched blackcaps and blue tits picking them off the leaves. 

One of the most striking features of the sycamore aphid is the way in which the individuals space themselves evenly under the leaf. the spacing is such that they are just close enough together to touch each other with their long antennae, so if an individual in one part of the leaf is attacked the alarm spreads from aphid to aphid in a wave of antennae-waving across the whole leaf.

The annual sycamore aphid population explosion has just about ground to a halt now and soon they'll fly to sites on twigs and buds where they'll lay overwintering eggs. They hatch in spring just as the buds burst, with perfect timing to plug their stylets into the fresh young foliage as it emerges - and that's the time when you'll often see blue tits and great tits picking the aphids off the bud scales.