Tuesday, March 29, 2011

The Insect that Turns Cars into Toffees

Take a close look at sycamore Acer pseudoplatanus buds at this time of year, just as they are beginning to swell, and you'll probably find some of these tiny insects huddled in groups around the edges of the bud scales. They're sycamore aphids Drepanosiphum platanoidis and they will have recently hatched from minute eggs that have survived the winter on the surface of the bark, just below the bud. It's often claimed that hard winters tend to reduce pest numbers, but that doesn't seem to be the case with this insect - buds on sycamores that I looked at today had a large pupulation of these aphids.

As soon as the tender new leaves begin to burst out of the bud scales the aphids will crawl onto them and begin to feed and breed - very rapidly. At this stage of their life cycle the aphids clone themselves, giving birth to live young that already have the next genetation developing inside them when they are born.

This is what the aphids look like at the moment, magnified about forty times. They cluster together with their antennae touching those of neigbouring insects, so any threats are transmitted through the colony very rapidly.

And this is what they do if they are threatened- all stick their tails up in the air. I'm guessing that they must be emitting something that might repel insect predators....

Once the sycamore leaf expands and begins to photosynthesise a winged generation of aphids develops. Later in the season these can migrate from tree to tree. Notice how most of them are lined up along the leaf veins. Their stylets, like hypodermic syringes, are inserted in the phloem inside the veins that transports the sugars, made by photosynthesis, to other parts of the plant. The sugary solution is rich in energy but very poor in other essential nutrients that the insects need for growth and reproduction, so they need to consume vast quantities of it, most of which is emitted from the tail end of the insect as sticky honeydew - and if you park your car under a sycamore on a hot summer's day when it's raining honeydew it will have the tactile qualities of a toffee when you return.

Sunday, March 27, 2011

Early Spring on the Durham Coast

One of the pleasures of living in a county like Durham, whose topography stretches from sea-level on the coast to the high Pennine hills that form the backbone of England is that you can extend the pleasures of spring. Today these primroses were in full flower on the edge of the sea cliffs just south of Seaham but it will be anything up to a month before the same species reaches this stage of development in the more exposed parts of Upper Weardale - offering opportunities for enjoying them over an extended period.

These violets were in bloom a little further along the cliff edge. I think this is hairy violet Viola hirta because I couldn't retect any scent, although you can never discount the possibility of the presence of sweet violet V. odorata genes, as these two early-flowering species hybridise.

Sunday's sunshine brought out the gorse flowers on the cliffs, with their distinctive aroma of coconut.

There were hundreds of coltsfoot blooms in the grass on the cliffs. The leaves won't appear for a couple of weeks, only expanding after the blooms begin to fade. The plant spreads via a creeping underground rhizome, so when you see a fine display of coltsfoot flowers covering a large area, to appreciate the full extent of the plant you need to imagine the network of underground rhizomes that connect them all together.

The flower buds of blackthorn (sloe) on the cliffs were on the point of bursting but I had to look hard to find one that had opened...

 This is a stonechat, perched on the thorn scrub and in fine voice, and ......

.... here's another, in handsome breeding plumage. 

When I turned over one of the limestone boulders down on the beach at Hawthorn Hive I found a family of pill bugs Armidillidium vulgare.

 When they find themselves threatened these little armoured crustaceans have a neat trick......

They curl themslves up.... 

....into an almost perfect armoured sphere and simply roll away into the grass....

Friday, March 25, 2011


This week saw one of the most memorable events of spring around here - the annual return of toads to their breeding ponds and the ensuing cacophony of croaking and orgy of mating that follows. They arrived in their hundreds, crawling out of the woods and over the wet grass to reach the pond where they grew up as toadpoles.

Some just floated on the pond surface, while....

.... others lurked underwater, but all had just one thing on their mind ...

.... finding something to mate with - and this one was so desperate that it tried to mate with my camera.

Somewhere in this writhing mass of toads there'll be a female.

This cluster slowly rotated in the pond for over an hour .... females are sometimes drowned by the lust-crazed males.

At one point this ball of toads had around eighteen individuals clambering over one another. This must surely be one of the most remarkable displays of blind instinct in British natural history. I saw a group of four toads trying to mate with a reed mace seed head that was floating in the water.

Many years ago, mooching around in a second-hand bookshop, I found a copy of Thomas Bell’s A History of Reptiles, published in 1849 when toads were still classified as reptiles. It provides some fascinating early insights into the life of these amphibians. Part of Bell’s purpose was to “shrew that it is.... highly useful, perfectly harmless, inoffensive, and even timid, and susceptible to no inconsiderable degree of discriminating attachment to those who treat it with kindness”, counteracting what he refers to as “undeserved persecution as the victims of an absurd and ignorant prejudice.... Condemned by common consent as a disgusting, odious, and venomous reptile, the proverbial emblem of all that is malicious and hateful in the human character....”.

This is one of the book's wood engravings. Bell provides a delightful description of a toad feeding: “The Toad, when about to feed, remains motionless, with its eyes turned directly forward upon the object, and the head a little inclined towards it, and in this attitude it remains until the insect moves; when, by a stroke like lightning, the tongue is thrown forward upon the victim, which is instantly drawn into the mouth.”

There are numerous old accounts of toads being found alive embedded in the wood of trees or even inside rocks (like the account you can read here), no doubt poorly observed instances of these animals hibernating under rotten logs and under rocks, and Bell describes some cruel experiments that were performed by early naturalists to prove that entombed toads could survive, including artificially embedding them in balls of hard clay or plaster of Paris ...... all of which inevitably led to the death of the toad.

Bell clearly liked toads and provides an account of how toads are easy to tame, citing his own pet toad that would "sit on one of my hands, and eat from the other..."

He also dispelled the myth that they are poisonous to humans - a long-standing misconception which you sometimes still hear repeated today. At one time it was believed that their bite, their breath and even a glance from those fiery orange eyes could strike you dead. Bell described how there are glands on their back that secrete an acrid liquid that deters predators, but that’s the limit of their toxicity. Bell went on to record how a Dr. John Davy investigated this secretion: “....... a thick yellowish fluid, which on evaporation yields a transparent residue, very acrid, and acting on the tongue like extract of aconite. It is neither acid nore alkaline; and since a chicken inoculated with it received no injury, it does not appear to be noxious when absorbed and carried in the circulation.”
You can see the glands in question - called paratoid glands in the photo above, showing up as the orange-hued ridges behind the eye.

Footnote: Thomas Bell, more than just a footnote in history.

Thomas Bell, a dentist by profession and author of A History of British Reptiles, was a remarkable individual. His personal researches into natural history were so admired that he became Profesor of Zoology at King's College London and he identified the reptile and crustacean species that Darwin brought back from his voyage on HMS Beagle, affirming that the giant tortoises were native to the Galapagos Islands and had not been taken there by pirates - a finding that was later to prove important in Darwin's interpretation of the way in which these reptiles had speciated on the islands. You can read more about him here.
Photo source: http://en.wikipedia.org/wiki/File:Zoologist_Thomas_Bell.jpg

Footnote: Batrachomyomachia

As with so many natural history books of the period, Bell’s account of the amphibians concludes with a charming tailpiece wood engraving, in this case of a battle between mice and frogs (double-click for a larger image).
It depicts the scene in a Greek poem sometimes said to have been written by Homer (unlikely, apparently) and probably dating from the fifth century BC, called Batrachomyomachia. In the story (there are numerous variations) a frog offers a mouse a ride on its back around its watery habitat but is frightened by a snake, dives underwater and the mouse is drowned. The tragedy is seen by a fellow mouse and a war, that lasts just one day, is fought between the mice and frogs. The goddess Athena calls on Zeus to quell the fighting using thunderbolts (i.e. an air-strike) but that fails and instead she sends an army of crabs (i.e. sends in the heavy armour) to quell the disturbance. You can read a translation of the poem here.

Sunday, March 20, 2011

For Our Eyes Only?

The first lesser celandines are coming into flower around here and it's a delight to see their glossy yellow flowers. One of the fascinating things about the flowers that we find so aethetically appealing is that the natural selective forces that have produced their colours throughout their evolutionary history have nothing to do with human vision and everything to do with the way that insects see the world. Many insects can perceive short wavelength ultraviolet radiation, that is invisible to us, but can't see as far as us into the long wavelength, red end of the spectrum. To grasp the implications of this it's useful to consider the colour purple, which is a combination of the extreme ends of the colour spectrum that we can see - blue and red. For an insect that can see shortwave ultraviolet radiation but can only see as far as yellow into the longer wavelength end of the spectrum the combination of these extremes is a colour that we can only guess at. What is certain is that a yellow lesser celandine doesn't look yellow to many insects.

While we can't know exactly what colours an insect's eyes and nervous system perceives, we can get some idea of how flowers look at the ultra-violet end of the spectrum that bees and some butterflies can see. This is a celandine flower photographed in monochrome using old fashioned silver halide black-and-white film (remember that?), using white light (sunlight).
This is the same flower using a filter that only passes ultra-violet light that's reflected from the petal surface. Notice how the centre of the flower - the location of the stamens and stigmas - strongly absorbs UV and how the petals themselves reflect it. This hidden pattern of UV reflectance acts as a target, zeroing the insect in on the important parts of the flower once it picks up the reflected UV light from the petal tips. Photographing floweres using UV filters reveals all sorts of cryptic UV absorbing and reflecting patterns that insects can see but which are invisible to us.

You can see more examples of flowers viewed in a way that insects might see them here 

Thursday, March 17, 2011

The Golden Age of Natural History?

I’ve often heard the Victorian and Edwardian eras described as ‘the Golden Age’ of natural history, when field natural history societies proliferated and flourished all over Britain. Excursions to study our flora and fauna provided a welcome diversion from the noise and grime of the Industrial Revolution in cities and studying natural history became an important part of the prevailing ethos for ‘self improvement’. David Elliston Allen in his The Naturalist in Britain: A Social History (Penguin, 1976) chronicles rise of the Field Clubs and mentions how 550 people once attended a single field excursion of the Manchester Field-Naturalists Society, which required the hiring of a special train. At the same time there was enormous public interest in new, spectacular discoveries of exotic animals in far-off places and during this period many of our great museum collections of natural history specimens grew rapidly. A few years ago I came across a little book that gives an interesting insight into one way in which this came about.

The Handbook of Instructions for Collectors was first published in 1902 by the British Museum (Natural History) – today simply known as the Natural History Museum – and in its preface the museum Director, E. Ray Lancaster FRS, set out its purpose:

   "In past years the Museum collections have been greatly augmented and enriched by the donations of valuable series of specimens obtained by travellers and others whose vocations have necessitated their residence abroad in all parts of the world.
   It often happens that military and naval officers, explorers, missionaries, and others have leisure time which they would be willing to devote to collecting natural objects if they had a better knowledge of the manner in which such things should be collected and preserved."

What follows is then a ‘wants list’ of specimens which, for mammals, included African elephants, scimitar oryx, sable antelope, Javan rhinoceros, Siberian elk, spectacled bear, Pacific walrus – published in the hope that if any of these wandered through the sights of a hunter's rifle in some distant part of the Empire the hunter would sell his trophy to the museum. Actually, what they really wanted was at least three specimens of everything, for reasons that Lancaster goes on to explain:

“In addition to this (and more especially in view of the approaching partial, if not complete, extermination of many species), it is of the highest importance that the museum should acquire a series of skins of all the larger species of mammals as a study collection, and also a duplicate set for future mounting, thus making three sets in all.”

The manual even includes this helpful illustration showing how to skin your tiger.

 What follows is detailed advice on collecting live and dead specimens of everything, from elephants to earwigs. Here are a few highlights:

“It is no easy matter to kill a large Tortoise or Turtle .... the traveller will consider whether it may not be possible to bring the animal to Europe alive, as it can live for ten or twelve months without food in some corner of the ship. If this is impractical a long knife should be thrust into the base of the neck in the direction of the heart......”

“Snakes of greater length than 10 feet cannot be preserved in spirit .... they must therefore be skinned.”

“Large pythons and boas are so frequently brought to Europe alive that most museums have opportunities of obtaining good skeletons; and therefore it is not worthwhile for a traveller to preserve them, unless they are of a size to verify reports in which Pythons exceeding 25 feet and Anacondas of over 30 feet are mentioned.”

“Some sharks attain a length of 30 feet, and some Rays a width of 20 feet; and according to very reliable reports, they may even exceed these limits. It is extremely desirable to obtain such gigantic specimens for museums”.

There were helpful tips for dealing with cantankerous customs officials too: “The opening of cases by Customs officers in docks and on the frontier of foreign states is often more fatal than a very long journey to the contents of the boxes. Bribery in such cases seems permissible, to ensure lenient treatment of collections”.

With hindsight, and unfairly judged by current standards of conservation ethics, all this sounds horrific but at the time it was perfectly acceptable practice for furthering scientific investigation and satisfying public curiosity about the living world. In some ways the Victorian and Edwardian eras were a Golden Age of Natural History Avarice, as far as the accumulation of specimens was concerned, even though it did lay the foundations of many aspects of biological sciences. Today many of the old-established naturalist's field clubs may be in decline but in many respects we are now in the real Golden Age of Natural History, when digital cameras and the world wide web allow naturalists - or anyone with curiosity and a willingness to pursue it - to record, disseminate and discuss their findings far more widely than our Edwardian ancestors ever could, from every corner of the planet.

Sunday, March 13, 2011

.......as the crow flies

"Turn east, then travel three miles as the crow flies...". How often have you heard that expression? Where does the idea of crows travelling in direct, uninterrupted flight lines, the shortest route between A and B - come from? Most crows that I've watched seem to be pretty easily diverted from the straight and narrow by anything that looks like it might be edible, like these two that were waiting to swoop on discarded chips on the seafront at Sunderland this afternoon...... so maybe that's where the expression comes from - their tendency to head straight as straight as an arrow for the nearest food supply. According to one web reference the earliest use of the idiom 'as the crow flies' dates only from 1767.

Tuesday, March 8, 2011

The Strangler

Back in 1597, writing in his Great Herbal or Generall Historie of Plantes, the herbalist John Gerard observed that " “Wood-binde or Hony-suckle climeth up aloft, having long slender woody branches........oftentimes winding it selfe so straight and hard about, that it leaveth its print upon those things so wrapped”...........

... just like this honeysuckle, growing in Hollingside Wood in Durham, is doing. It's climbing up a young rowan and the end result looks like a life-or-death contest between two writhing serpents.

The tightly coiled honeysuckle has scarred the rowan trunk but as the tree trunk expands it's beginning to grow over its strangler....

.... and lower down, near the base of the tree, the bark has almost completely healed over the top of the honeysuckle's stem. Give it a few more years and the honeysuckle stem will be absorbed into the lower part of host trunk entirely - a climber inside its host. So who is strangling whom?

The tree is struggling but the honeysuckle is thriving - and coming into leaf nicely.

For more on honeysuckle, click here.

Saturday, March 5, 2011

Slither, Slither....

Whenever gardeners gather together in spring, sooner or later the conversation comes around to slugs, those destroyers of horticultural dreams. So, bearing in mind the words of the 6th. century BC Chinese military strategist Sun Tzu - "If you know both yourself and your enemy, you can win a hundred battles without a single loss" - here are pictures of two of the worst offenders. Double-click for larger images. First up, the netted slug Deroceros reticulatum, which so often crawls into lettuces. The colour can be quite variable but this pale grey and buff form is common in my garden, but...

... the ID character that gives this slug its common name is the dark network pattern on the tail end of its body, which you can just see in this view, at the back of the animal.

And here's another slug that will be slithering out in search of tender young seedlings as soon as mild, moist spring days arrive. This is the Budapest slug Milax budapestensis. In this view you can see the open breathing pore (the pneumostome) that leads to the slug's lung. Those little parasitic nematodes that you can buy to kill slugs, as an environmentally-friendly alternative to slug pellets, crawl in through there, breed and kill their host.

The Budapest slug has a distinctive yellow keel that runs along the top of the rear half of its body.....

... and the pneumostome is located towards the back of that 'saddle' at the front of the body, while.....

... the dark stripe that runs along the underside of the foot is also a distinctive feature.

One of my project students, Jack Brooks, is currently investigating whether there are any natural extracts from plants that might be used to deter slugs (they are supposed not to like garlic, coffee and extracts of ivy leaves) that could be used to protect vulnerable seedlings in spring. He's also looking at which garden slugs are damaging and which are harmless to plants - the leopard slug (sometimes called the great grey slug) is supposed to be blameless as far as damage to garden plants is concerned. We'll report back on how the research goes....

Wednesday, March 2, 2011

Mossy Invader

The invasive alien plant species that tend to hit the headlines are the large ones - like giant hogweed and Japanese knotweed - but there are smaller species that have snuck in largely unnoticed and have become an almost ubiquitous element in our flora. This is the Cape Thread Moss Orthodontium lineare which was unknown in Britain until 1922, when a bryologist called E.V. Watson found it on some rocks in Cheshire. Since then it has spread the length and breadth of the British Isles. It comes from the southern hemisphere, from Africa, South America, Australia and New Zealand, but until Watson found it the moss was unknown in Britain. Those drooping spore capsules are a distinctive characteristic and the fact that they are produced in such profusion in spring and release so many spores goes a long way to explaining how it has spread itself around so effectively.

Tuesday, March 1, 2011


These strange objects are the pollen-producing structures of a yew tree. There are separate male and female trees and at this time of year these little pollen-producing cones, known botanically as strobili, are very conspicuous on the male trees, releasing pollen that's carried on the wind to the females. Yew belongs in the division of the plant kingdom known as the gymnosperms that includes the cone-bearing conifers, but unusually it doesn't produce its seeds within a woody cone. Instead each seed is carried in a succulent red cup, which you can see by clicking here.