One species, three disguises: three beautiful spiders

I have had real difficulty in identifying these three spiders, all found at the weekend, but now, thanks to help from Dave Jewsbury at the Hampshire and Isle of Wight Wildlife Trust, it's clear that they are all the same species - Metallina segmentata, which is described in spider guides as being 'extremely variable in markings and colour'. You can say that again .....

Thanks Dave.

This one lurks in a Genista bush in our garden ...

...... and this beauty was hiding between the leaves of an elm near the river Wear at Wolsingham. Those markings on the abdomen call to mind a fine cracked glaze on a high quality ceramic.

Finally, this one was sunning itself on a brome grass stem.

Nettle and meadowsweet galls

These strange swellings on leaves and leaf petioles of stinging nettle are the work of a gall midge called Dasyneura urticae, whose larvae develop inside the pouches. The midge lays its eggs on the leaf upper surface and when the larvae hatch they irritate the plant tissue on either side of the the groove in the leaf ribs, which grows over them forming a protective pouch lined with nutritive tissue. When the larvae are fully developed they escape through a slit in the gall wall and fall to the ground, pupating in the soil. 

You can find some excellent photos of the midge and its larvae at this web site

These are gall midge galls of another species of the same genus, Dasyneura ulmaria, on the leaf of meadowsweet Filipendula ulmaria. The galls and life cycle of the insect are broadly similar but in this case the midge lays its eggs on the underside of the leaf and there is only one generation each year.

All photos taken at Romaldkirk in Teesdale on 25th. September.

More photos of plant galls here.

Lovely Legs

Today's Guardian Country Diary is about encounters with harvestmen while clearing an overgrown garden.

Although they're often referred to as harvestmen 'spiders' they belong to a quite different taxonomic order from true spiders and have none of their menace, mainly because they lack large poisonous fangs but also because of the tentative, non-threatening, painstaking way that they move. Those long legs are not just for walking - the second pair also carry their senses of touch and smell, which are far more sensitive than their single pair of tiny eyes that are mounted on a turret on their topside. 

When you watch a harvestman on the move it gently feels its way over new territory by extending that extra-long second pair of legs, constantly touching the ground ahead and picking up scents. If you put two harvestmen together in a confined space they'll each extend their second pair of legs towards each other, picking up each others' scent.

Harvestmen scavenge dead animals and will eat fungi and drink juice of ripe fruit, but they are also hunters, catching and eating animals smaller than themselves. There is one intriguing account of a harvestman penning up its prey within a circle of those long legs, drawn close-in to its body, then dropping on its prey like a pile-driver. 

A variety of animals prey on harvestmen, including frogs, toads and birds. On a couple of occasions I've seen robins with their beaks full of harvestmen in autumn. 

They have two forms of defence. One is the secretion of a noxious fluid, said to smell of walnuts, which will deter small predators like ants. Their last line of defence is autotomy - the shedding of legs to allow then to escape a predator's grip (or the sticky threads of  spider's web). It's common to see harvestmen with fewer than the full complement of legs at this time of year but if they lose the second pair - and with them their vital senses of smell and touch - they stop feeding, essentially losing the will to live.

This is the pose adopted when they're faced with a threat, with that second pair of legs extended as wide apart as possible - assessing the threat by detecting its scent.

Although they tend to move slowly and precisely they can, if the need arises, run with considerable speed over uneven surfaces - like long grass, for example - thanks to those amazingly long legs that allow them to simply step over objects that would slow shorter-legged animals down.

At this time of year harvestmen will be laying eggs, which will overwinter and then hatch  next spring as nymphs, which will then slowly grow larger as the summer progresses.

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Beauty in the eye of the beholder (provided you have a hand lens)

When I started out in botany the first field guide I owned was McClintock and Fitter's Pocket Guide to Wild Flowers, which used a one-, two- or three-star system to indicate rarity. And I was obsessed with finding rarities (though not very successfully). I still get a buzz out of finding something uncommon but have come to appreciate the subtle charms of the less ostentatious wild flowers, realising that if you can't see anything interesting about a plant then you probably aren't looking closely enough.

Here's a case in point: knotgrass Polygonum aviculare. This is the rather attractive little flower, which is only a few millimetres in diameter ......

...... and this is the scruffy plant, growing in a gap between the paving stones in our garden path. I must have trodden on it scores of times as I've been walking up and down the path, but now I've looked more closely at the flowers I tend to step over it.

Its tiny seeds probably provide food for the sparrows that are always fossicking in the crevices in the garden path.

In his Weeds and Aliens (1961) Sir Edward Salisbury mentions that in sandy soils the tap root of this tough annual can penetrate to a depth of three feet and that its seeds remain viable for up to sixty years.

The Perils of Picking Over-ripe Plums

I learned the hard way that seemingly perfect ripe plums can be hollow on the side that you can't see when you reach up to pick them, and likely as not contain a feeding wasp, so these days I always wear gardening gloves when I pick them.

This is probably what wasps dream about, when the hard work of raising a brood is over ......

....... spending their dotage chewing their way through a sweet, juicy plum. I piled some on our bird table and after the last couple of days of warm weather they've begun to ferment, so the wasps are becoming woozy on alcohol and are very approachable. Sometimes they are so inebriated that they fall over on their backs if you give them a gentle shove; reminds me of my student days.

They  need to take frequent feeding breaks to clean sticky juice off their legs ....

.... and faces.

There are some pictures of some rather different inebriated insects on rotting plums here.

The 'Wow' Factor

This stunning chain-saw sculpture of a red kite stops you in your tracks when you round a bend in the Thornley Wood Sculpture Trail near Gateshead. I think everyone who encounters it has only one word to describe it: "wow!"

You can read more about its creator here,and here and see some other enterprises and artworks that have been inspired by the reintroduction of red kites into the Derwent Valley here...........

... and see another example of Tommy's chain-saw work here.

More tales from the compost bin: millipedes

Another player from the cast of thousands whose daily dramas are played out in our compost heap - in this case ....

.... a flat-backed millipede Polydesmus angustus, going head-to-head with a springtail. Flat-backed millipedes feed on rotting plant material so the springtail isn't under serious threat...... unless it's about to be trampled by a large number of feet.

Flat-backed millipedes are very good climbers - this one climbed the near-vertical outer wall of the plastic compost bin with no difficulty.

Two early-autumn flowering members of the gentian family on the Durham coast

Both of these members of the gentian family (Gentianaceae) were in flower near the limestone quarry south of Seaham on the Durham coast today.

The delightful little felwort, Gentianella amarella ..........

......... also known as autumn gentian .......... and

....  yellow-wort Blackstonia perfoliata, whose leaves are perfoliate - i.e. they have no stalk and the plant stem runs right through the centre of them.

Walking on water ....

I didn't realise that this spider was living under the lid of our water butt until I lifted the lid and the spider fell into the water. I thought it would need rescuing because, as you can see from the photo, most its legs had penetrated the surface film. But it was made of sterner stuff .....

.... and, resting its hairy waterproof body on the surface, it heaved its legs out of the water as if it was wading through treacle, lifting them high in the air, as with the left fore-leg in this picture, then ....

..... it rested each hair foot on the surface film and scooted across the water surface to the edge of the water butt and climbed out, none the worse for wear.


I guess it probably lived under the water butt lid because it liked the relatively warm, humid atmosphere - that large mass of water retains heat well into the night .......... and there are also plenty of prey items that crawl in under the rim of the lid.

I'll be a bit more careful next time I lift the lid. 

Africa Gomez has very kindly identified the spider for me as a female Amaurobius similis.

A "lousy watchman"

We found this magnificent Dor beetle Geotrupes stercorarius when we were helping to clear an overgrown garden at Winlaton Mill near Blaydon yesterday. 

The armour on these lumbering insects is incredible - just look at that thick plate on the forehead and between the eyes, and those serrated edges to the legs; they're built like a battleship. Those clubbed antennae are unusual too. 

When we picked it up we noticed that there seemed to be something unusual going on at its rear end and tipping it on its back revealed the cause....

..... a dense cluster of parasitic mites under its tail. Most dor beetles seem to be infested with these, giving them an alternative colloquial name of the 'lousy watchman' - presumably because that are often found after dark near lights - like night watchmen.

Blue iridescence is a feature of the underside of these beetles.

Turning it on its back also induced it to open its wings ...

..... as well as exposing its tormentors. Despite its armour it has no real defence against the mites, which attach to the softer articulating tissue between the plates of its exoskeleton. Here it's trying, unsuccessfully, to dislodge them with weak movements of its hind leg. 

Dor beetles breed in chambers under cow or horse dung, dragging the dung into their burrows to feed their grubs.

It quickly righted itself and them rampaged across a gardening glove, looking mighty annoyed. The aerofoil profile of its extended elytra, that are held rigid in flight while the wings beat under them, is nicely displayed in this photo (double click for a larger image).

It looked like it might fly but never quite managed take-off, folding its wings under its elytra instead.


There's a fine picture of a dor beetle in flight on the ARKive web site - click here

For more pictures of animals infested with mites, click here , here and here .

Plant galls

This is probably the best time of year for anyone interested in plant galls - those strange growths on plants caused by insects, mites and sometimes fungi. These are a few that I've seen locally over the last couple of weeks.

Leaf petiole of common lime Tilia x europaea with a gall chamber containing larvae of the gall midge Continaria tiliarum.

Ash flowers galled by the ash gall mite Eriophyes fraxinivorus.

An old oak apple gall caused by the gall wasp Biorhiza pallida, with exit holes where the adults have hatched.

Silk button galls on the underside of oak leaves, containing larvae of the gall wasp Neuroterus numismalis

Spangle galls on the underside of an oak leaf, containing larvae of the gall wasp Neuroterus quercus-baccarum.

Galls on leaf surface of sycamore caused by the eriophyid mite Eriophyes macrorhynchus aceribus. Click here for pictures of eriophyid mites.

Bean gall in the leaf blade of willow, containing the larva of the sawfly Pontania proxima

Robin's pin cushion or bedeguar gall on wild rose, caused by the gall wasp Diplolepis rosae. 

For pictures of the gall wasp click here. 

For pictures of the parasite that attacks the wasp, click here.

The mysterious attractions of black berries

Thursday's Guardian Country Diary focuses on bird cherry Prunus padus, which has produced an exceptionally fine crop of its beautiful black fruits in Weardale this year. This is probably the result of excellent flowering conditions in late spring, fewer small ermine moths that often defoliate the trees and fewer instances of pocket plum disease which can destroy the fruits before they ripen.

Most wild fruits that are dispersed by birds are red (hawthorn, rowan, guelder rose and honeysuckle, to name but a few), so how come bird cherries (and also blackberries, buckthorn, deadly nightshade and elder berries) are black? Is fruit colour of any great significance for fruit-eating birds?

Over the last few decades there have been several scientific investigations into the ways in which fruit colours attract birds, addressing the question  'why are some ripe fruits red and others black?'

So here's a selective summary of some findings to date:

1983.
A study in the US using black cherry Prunus serotina concludes that it's not the final black colour of the ripe fruit that's important in attracting birds, but the mixture of intermediate red-coloured ripening fruits and black fruits that attract birds' attention. They observe the same results with pokeweed Phytolacca americana, whose fruits change from green to pink to black, and the conclusion is that the bicoloured phase of fruit presentation is important, rather than the final ripe colour. 

1999.
Unlike humans, birds can perceive ultra-violet light so the colours that they see don't correspond to our perception. Blue, violet and black berries reflect ultra-violet light, which may make them more conspicuous to birds and indicate their stage of ripeness. The bloom on the surface of bilberries (which is caused by a surface layer of yeast) reflects UV. When redwings were allowed to choose between bilberries with the bloom on the surface and others where the bloom had been polished away adult redwings preferred berries with the UV reflecting bloom, but inexperienced juveniles didn't distinguish between the two, suggesting that the birds learn to associate UV reflectance with fruit ripeness. 

2003
Another study revisits the bicoloured fruit hypothesis from 1983 and finds evidence to support it. 

2004.
Another study with juvenile redwings, which initially prefer red fruits but learn to associate black/UV reflective fruits with palatability, suggests that learning plays a key role in fruit colour choice. The study suggests that the colour of the fruits, not the contrast between their colour and the background, is particularly most important. 

  
2004
Another study that examines the relative significance of fruit colour and the contrast between fruit colour and background colour concludes that red and black fruits contrast more strongly with background foliage colours than any other fruit colours, which may be why they predominate. Tests on four bird species indicate that it's conspicuousness relative to background colours, not fruit colour itself, that's most important to foraging fruit-eating birds.

2006
Tests with crows in a flight cage conclude that artificial  red fruits are more conspicuous to them from a distance than artificial black fruits. When the crows were offered blueberries with or without their UV reflecting bloom, they were more successful in finding the UV reflecting ones - but that also depended on how UV-reflecting the background was.

2009.
A study concludes that blackcaps preferentially eat black or UV-reflecting fruits, choosing those with the highest intensity of colour, and that these darker fruits have high purple anthocyanin pigment antioxidant levels (good for their health) and also higher energy content. 

2009
A  study shows that birds can preferentially select ripe elder berries that have red stalks (indicative of high anthocyanin content) or ripe elder berries with green fruit stalks (that make the fruits more conspicuous and indicate a higher sugar content) - all suggesting that birds don't just gobble fruit down, they can be picky eaters and make dietary choices based on fruit quality.

2011
Studies using captive blackbirds and redwings that are offered artificial fruits show that blackbirds preferentially choose red fruits whereas redwings prefer black ones, but that these preferences can change depending on previous experience - they tended to prefer fruits of a colour that they had previously fed on, so learning was important.

2011
A review of the literature on the subject concludes (a) there is evidence that fruit colour is an important signal that birds react to; (b) that black fruits high in antioxidants (purple anthocyanin pigments), which tend to be formed in the fruits in bright light under cold conditions, enhance the immune systems of blackcaps; (c) that high levels of antioxidants reduce the fruits' proneness to fungal attack, benefiting the plant and suggesting that black fruits might have originally evolved for this reason, rather than to attract birds. 


So, back to the original question :'why are some ripe fruits red and others black?'. In summary, it's all to do with - 

- the fact that these are the two colours that birds find most attractive

- that the mixture of reds and blacks in a branch of ripening fruit (think of blackberries ripening from pink to black) may be important in attracting birds' attention

-  UV reflectance (that we can't see) is very important especially in fruits like blueberry, bilberry and sloe that have a UV-reflecting surface 'bloom'.

- that the contrast between the fruit colour and background colour is important

- bird species may have innate preferences but these can change when they learn to associate colour with fruit quality

- some birds can select fruit, on the basis of colour signals, that has higher nutritional value

. black colour, with high antioxidant anthocyanin pigment content, might have evolved in plants as a defence mechanism against fungal disease rather than to attract birds.

As is so often the case, there are no easy answers; scientific research rarely delivers simple explanations but always produces a whole raft of more interesting, more sophisticated questions. 

Which is why science is so addictive - the natural world is always far more complex than anyone can possibly imagine.

As for the birds in my garden:

- the blackbirds and thrushes never touch yellow-berried holly but eat all the red berried holly as soon as it ripens.

- waxwings and bullfinches only eat the yellow fruit of 'Golden hornet' crab apple when it goes brown and begins to rot. If you want to attract birds to a garden in autumn, don't plant yellow-fruited trees and shrubs

- blackbirds go mad for the blue, bloom-covered UV reflecting, high anthocyanin containing berries of red flowering currant and Berberis - there's purple-stained bird poo all over our garden right now!


Click here for two more long-standing botanical mysteries

Sources:

Willson,M.F. and Melampy, M.N. (1983) The effect of bicolored fruit displays on fruit removal by avian frugivores. Oikos 41: 27-31.

Siitari, H; Honkavaara, J; Viitala, J (1999). Ultraviolet reflection of berries attracts foraging birds. A laboratory study with redwings (Turdus iliacus) and bilberries (Vaccinium myrtillus). Proc.Roy. Soc (B) 266,2125-2129

Jennifer M. Cramer, Maria L. Cloud, Nathan C. Muchhala, Anastasia E. Ware, Brent H. Smith and G. Bruce Williamson (2003) A test of the bicolored fruit display hypothesis: Berry removal with artificial fruit flags. Journal of the Torrey Botanical Society 130, 30-33

Honkavaara, J; Siitari, H; Viitala, J (2004) Fruit colour preferences of redwings (Turdus iliacus): Experiments with hand-raised juveniles and wild-caught adults. Ethology, 110, 445-457

Schmidt, V; Schaefer, HM; Winkler, H (2004) Conspicuousness, not colour as foraging cue in plant-animal signalling. Oikos 106, 551-557

Schaefer, H. Martin; Levey, Douglas J.; Schaefer, Veronika; et al. (2006) The role of chromatic and achromatic signals for fruit detection by birds. Behavioural Ecology 17,784-789

Schaefer, H. M.; McGraw, K.; Catoni, C. (2008) Birds use fruit colour as honest signal of dietary antioxidant rewards. Functional Ecology 2, 303-310


Schaefer, H.M. and Braun, J . (2009)  Reliable cues and signals of fruit quality are contingent on the habitat in black elder (Sambucus nigra). Ecology 90, 1564-1573.


Larrinaga, Asier (2011) Inter-specific and intra-specific variability in fruit color preference in two species of Turdus. Integrative Zoology 6, 244-258


Schaefer, H.M. (2011) Why fruits go to the dark side. Acta Oecologica 37, 604-610.

I made my excuses and left ........

The compost bin at the bottom of our garden recycles all our vegetable-based kitchen waste and every time I lift the lid it reveals a new population of animals, most of them small ........

.... like this hairy little owl midge, about three millimetres long. 

This minute juvenile woodlouse, also just a few millimetres long and looking like it's not old enough to be out on its own, was lurking under the bin lid. To give some idea of how small it was, compared with a full-sized woodlouse ....

........... here's a slightly larger juvenile (about three times the size of the one above), under the watchful compound eyes of a full grown woodlouse.

The prize for the most numerous insects in the compost bin must go to these minute flies, smaller than the owl midges, that breed with amazing speed and in incredible numbers on the decaying fruit and vegetable peelings. Every time I lift the lid I have to step back as a small cloud of them takes to the air. I rarely see singleton flies of this species, because they seem to be ......

.... perpetually mating, in this push-me-pull-you conformation.

When I was a callow youth I used to frequent a barber's shop where they always had a pile Reveille and Tit-bits magazines for customers to leaf through while they waited for a trim. For those unfamiliar with these fine publications (long-since defunct),they specialised in 'tasteful' glamour photos of ladies who seem to be having trouble keeping their clothes on, together with sensational and highly improbable stories (of the 'My ordeal amongst cannibals' variety), Daily Express style editorials about the country going to the dogs ('What has happened to our national pride?) and investigative journalism that lifted the lid on the licentious behaviour of the ruling classes. The latter always involved intrepid undercover reporters visiting sordid establishments in Soho, witnessing goings-on that mostly seemed to involve clergymen, Members of Parliament and burlesque dancers ..........

.......... engaged in this sort of activity. 

The pay-off line for such stories was almost always "disgusted, your reporter made his excuses and left". 

Which is what I did after I lowered the compost bin lid on these three and plunged them back into darkness.