Chapter 3

One Thousandth Of A Metre

We’re coming back to familiar things now. The great blobs on the lens that were just misty patches are finally slipping into some sort of focus, and a whole raft of life forms are dropping by the wayside as we pull out and change our scale to something far larger: the tiny fragments of plankton that fill the oceans; the dusty fungal clouds in the evening air; the singular amoebas that live wherever there is moisture – all wonderful subjects, but for another time. I just can’t seem to get the focus right though: the nematodes are everywhere. Where should I start?

What about soybeans?

I have just found out that The Society of Nematologists is advertising the 4^th National Soybean Cyst Nematode Conference. A whole conference about the egg filled bodies of a specific nematode worm that affects a specific crop. This being the fourth one you might be forgiven for accusing the organisers of being a little overenthusiastic – maybe they are scientists ensuring they have their research grants for another year; maybe they are companies trying to sell a product; maybe soybean cyst nematodes are actually very important indeed. Actually it’s all three. Scientists need to justify their work so they can keep on working: unfortunately, whereas justification used to be on mostly scientific grounds, justification in many modern universities requires evidence of commercial potential. Pest control companies need to raise the profile of the “pests”[i] they sell control products for, so they can sell their products to worried consumers. Finally, according to the US Department of Agriculture[ii], the cultivation of soybeans is not economically possible unless soybean nematode cysts are sufficiently controlled.

A glance at the literature on nematodes reveals two things: they are apparently almost all damaging pests, and there are an awful lot of them. To answer the latter point, many writers turn to the words of N.A.Cobb, legendary nematologist, and stalwart of the US Department of Agriculture in the first half of the 20^th century:

In short, if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites.[iii]

Stirring stuff, indeed. Nathan Cobb could certainly move the soul when writing about his foremost passion; and he needed to, because if ever a biological subject needed a higher profile, it was the much-maligned, but utterly fascinating world of nematodes. Cobb himself recognised this problem, writing: “[nematodes] offer an exceptional field of study, and probably constitute almost the last great organic group worthy of a separate branch of biological science comparable with entomology.”[iv] But was Cobb right? Do nematodes really create this film of organic matter around every object in contact with the Earth?

There is a certain difficulty in gaining realistic statistics about the variety and quantity of nematodes; after all nematodes were not formally discovered until 1808, principally because they are too small to observe properly with the naked eye. Victor Dropkin made a more sober assessment than Cobb of the nematode population in 1980, stating: “Take a handful of soil from almost anywhere in the world…and you will find elongate, threadlike, active animals. These are nematodes. Or catch a fish, a bird or a mammal almost anywhere in the world…and in most cases you will find some nematodes inside.”[v] Although nematodes are aquatic animals, in that they need water to survive, the best place to find them is in soil. Simon Gowen of the University of Reading, tells his students that in temperate grasslands there are around nine million nematodes for every square metre of soil – then the same students are expected to count them for themselves (not all nine million of them, I hasten to add), just to get an idea of what this means. That is an astounding figure for something that is not a virus or a bacterium, but an animal. This means that the lush grasslands of New Zealand that produce rich butter, high quality lamb and 150 thousand tonnes of wool[vi] each year, but only constitute 5.5 percent of New Zealand’s land area, also hold something like 132,660,000,000,000,000 nematodes. That’s 132 quadrillion, for those of you who ever wanted to know how large a quadrillion is. Compare this to the apocryphal (but believable, and slightly disturbing!) figure of one million spiders per acre of grassland, and you find that nematodes outnumber spiders by 36,000 to 1.

Globally – and I’m going to have to take an outrageous stab in the dark here – you are probably looking at between 100 quintillion (that’s 20 zeros) and 1000 quintillion (21 zeros) nematodes on and in the land. To put this into perspective somewhat: for each human on Earth, there are something like a trillion nematodes. Nematodes in the oceans are far less abundant, but there are still lots and lots of them – they may, in fact, account for ninety percent of all life at the bottom of the sea[vii]. Sorry for boggling you with figures, but that’s what often happens in nematode-land.

The pest control industry ensure that the dangers that would be unleashed in a world where nematodes are not controlled are writ large in the minds of farmers, so it is the “pest” nematodes that are given the biggest exposure, at the expense of other types. Despite the commercial world’s propensity to invent problems in order to sell products they may, in this case, be right – but for all the wrong reasons. The pressure we place on already exhausted soils and the effort we go to in order to extract every last gram of nutrition from industrially farmed crops to feed a growing human population (both in number and, in rich countries, appetite), means that the slightest drop in the production of a staple crop is treated as a potential catastrophe.

In the majority of European countries, the impact of the potato cyst nematode (PCN) is such that the movement of untested seed potatoes and the planting of potatoes on untested land is banned, and the quarantine of land on which PCN is found is mandatory[viii]. PCN is a global problem for potato growers, being found across Europe (since 1913, and possibly the 1880s), in Australia (since 1986), in the USA (since 1941) – in fact just about everywhere that potatoes are grown on a large scale. There are quite a few varieties of potato that are naturally resistant to the effects of PCN which, essentially, means not being in danger of having entire crops wiped out within two seasons of growing on the same spot; and there are lots of sensible, non-chemical methods of avoiding the problem, such as the aforementioned quarantine, crop rotation and the use of natural predators. But the chemical companies persist in pushing their wares, both in the form of pesticides and genetically modified organisms (GMOs):

The chemical group BASF has expressed optimism that within a few weeks the European Commission may approve the genetically modified “Amflora” potato to be grown in Europe. In early December, Hans Kast, Managing Director of BASF Plant Science, spoke with journalists in Brussels and stated the expectation the decision be made in any case early enough for the growing season of 2008.[ix]

It won’t be too long before natural resistance to PCN is engineered into non-resistant potato varieties. Now, I am no scaremonger when it comes to genetic modification, but when economic gain comes before concerns for environmental welfare – the GMO producing companies still obstinately refuse to accept liability for any negative effects of their products – and the number of discovered nematode species is less than ten percent of the number that potentially exist in the wild, then I start to get a little worried.

Then there is the question of pest versus friend:



Figure 4 : Nematode Adverts (Source: Author’s image)

Yes, those are adverts from Google. It’s remarkable what is advertised on the Internet: not so much the availability of salacious activities and products to enhance your performance in all sorts of ways, but the wide range of friendly nematodes that you can use in your garden, and can buy on line. Nematodes in a box. I think it’s about time we stopped for a little and went back to first principles.

What Are Nematodes?

Remember me saying that I had problems getting the focus right? There are teeny-tiny nematodes and there are, relatively, very large ones indeed. I admit the title of this chapter takes a few liberties, but there are many species of nematode that are around a millimetre in length. There are many that are less than a millimetre, and some parasitic types that are a few centimetres long. One type (which no one alive seems to have seen) was measured at eight metres long, in the placenta of a sperm whale. This species is, unironically, known as Placentonema gigantissima.

Nematode is the name given to any one of at least 20,000 species of unsegmented worm, which have a single end-to-end digestive tract, no limbs or other appendages, and a surprisingly well-developed nervous system, considering their antiquity. They are commonly known as “roundworms”, which describes their cross section, not their overall shape, and which distinguishes them from many other types of worm, including flatworms and bristle worms.

Such is their age and diversity (although this does not always follow) that they occupy their own Phylum, separate from the arthropods (insects, spiders etc.) and molluscs. There are as many as twenty different Orders of nematode, ranging from those that attack plants and fungi, to those that feed on other animals, to those that drift around feeding on whatever bacteria or single-celled animal might be available. Despite nematodes being aquatic in origin, the vast majority of Orders describe land-based varieties. This strange inconsistency is most likely simply because the world’s oceans have been so poorly researched compared to the land masses we are so familiar with. Our natural, possibly ancestral attraction to the sea, a place that has always (until recently) provided us with a rich source of food, only goes so far. Like gasping fish on the water’s edge, humans immersed in water will only survive for a few minutes – less if it is particularly cold. Maybe it is for the good that much of the vast oceanic world has been left unexplored – the level of exploitation by the oil, gas and industrial fishing industries is a dire warning of what can happen – but it does leave us with a large empty space in our knowledge, and the consequent skewing of information that suggests that the oceans are a vast, barren place. Sadly, that lack of knowledge also hides the inexorable, and possibly irreversible changes that we may be causing to the oceans.

Because nematodes can look very similar, regardless of their size, they are most commonly distinguished by their mouth-parts, which define what they are able to eat. Nematologists do have what some might consider to be an unhealthy obsession with mouth parts, but when you have a great mass of seething, wormy matter to identify, then it’s usually best to take the easy route. Such efforts are not without their rewards though: success in the field of nematology can be quite lucrative if you don’t have any qualms about taking the corporate shilling.

The multi-segmented tapeworm that can live for years inside humans and most other mammals is not a nematode; human parasitic threadworms and hookworms, on the other hand, are nematodes. I’m sorry to enter the bowel, as it were, at this stage of the chapter, but if you have had anything to do with children’s health or education then you will probably have come across threadworms. Unfortunately for human health, children have a propensity to pick, scratch and probe anything and everything with their fingers: noses, scabs on knees, eyes, bottoms. Under the nails of a good proportion of kindergarten children just about anywhere in the world lie a little cluster of threadworm eggs waiting to be passed into the digestive system (you can guess how) of that child, or any other person they may meet: “How do you do?” and with a shake of the hand the eggs are passed on. Fortunately for us, threadworms are relatively harmless.

There are a number of other parasitic nematodes that infect humans, and other mammals: in dogs, hookworms can cause severe anaemia, and in both dogs and cats the roundworm Toxocara is endemic. The latter is of particular concern to humans because of the potentially severe symptoms that the resulting Toxocariasis can lead to, including blindness and pneumonia. Studies carried out between 1985 and 2000 found that children’s sandpits in public parks contained Toxocara eggs a minimum of 25 percent of the time, with one study in Greece finding 97.5 percent of play parks infected.[x] A child who touches dog or cat faeces will almost certainly have nematodes on his or her fingers. This level of infection may be shocking, but it is the hygiene failures of humans that have turned something pretty benign into something approaching epidemic proportions in certain parts of the world. This lack of hygiene makes the little press nematodes get predominantly negative – which is a shame because, like humans, not all of them are bad.

The Good Guys

Good organic gardeners know how to deal with pests – the kinds that damage the crops they are trying to grow. A piece of fruit or a vegetable is at its most appealing to birds, insects, slugs and snails at just the time when it is at its most appealing to us; the sugar-rich strawberry, the fat-to-bursting pea pod, the succulent red tomato, the crisp crimson and white radish – all perfect for eating, regardless who the final consumer may be. Good organic gardeners don’t need to spray chemicals across their gardens, to be caught by the wind and misted across the neighbouring crops, flowers and ponds, and into the lungs of playing children: they just need to understand the natural interactions between plants, soil, weather and the organisms that may protect or attack what they are trying to grow.

The history of pesticides (that kill animals), herbicides (plants) and fungicides is littered with toxins that no sensible person would let anywhere near their mouths. We see arsenic being widely used for pest control on plants and even as sheep dip; mercury, formaldehyde and hydrogen cyanide used to fumigate buildings and glasshouses; and the surprisingly lethal copper sulphate applied as a common weed killer[xi]. Paris Green derived its name from its colour and its use as a rat control agent in the sewers of Paris in the 19^th century. Alternatively known as Parrot Green and Emerald Green, amongst other names, it is a compound of copper and arsenic, and is still widely used as a barnacle prevention measure on the hulls of ships, and a wood preservative, as well as an insecticide. Seven drops of this, surprisingly unregulated, substance is enough to kill a normal sized human[xii], and its death toll almost certainly includes many artists who keenly made use of its vivid tones; not to mention the poor souls who made the stuff. It seems that if a substance is useful enough then being lethal in tiny doses is not enough reason to regulate it.

The use of cyanide, mercury and formaldehyde may have been dramatically reduced during the 20^th century, but given the boom in the use of organophosphates and organochlorines (“organo” simply means something that is carbon based), such substances were not required much anyway. The world now had cheap, highly effective and controllable – so it seemed – agents that could be applied at will. Of course, as we know now (and, no doubt, the manufacturers already knew early on) the legacy of these chemicals was passed into the water, and from mother to child in countless animal species, including humans. There is no way of knowing how many cancer deaths have been caused by chemical pesticides, nor any way of predicting how many more deaths will come as their legacy lives on both in the bodies of fish and marine mammals, and also those parts of the world where such pesticides are still commonly used with relish.

Organic gardening and farming have been practiced for far longer than chemical based growing, and nematodes can play an important part in this. Remember those I mentioned that feed on other animals? Well, there is a whole range of different species that not only leave the plants you are growing well alone, but also actively destroy the very creatures that would otherwise cause damage. Technically, these are known as Entomopathogenic[xiii] nematodes, and there are two main species that are used: Steinernema and Heterorhabditis (don’t worry; I won’t be testing you later). They are similar in form and effect, both killing a wide range of insects and related organisms, like caterpillars, by entering their bodies as juveniles then releasing bacteria that are toxic to the host. This bacterium kills the insect, after which the nematode is free to mate or, in the case of Heterorhabditis, reproduce alone.

The downside? Well, there really isn’t one, unless you count having to make sure they are not fried by ultraviolet light, or overheated. I include this quotation from Cornell University, just to show I am not overstating the advantages of these wonders:

Entomopathogenic nematodes are extraordinarily lethal to many important soil insect pests, yet are safe for plants and animals. This high degree of safety means that unlike chemicals nematode applications do not require masks or other safety equipment; residues, groundwater contamination and pollinators are not issues. Most [other] biologicals require days or weeks to kill, yet nematodes, working with their symbiotic bacteria, kill insects in 24-48 hr.

Dozens of different insect pests are susceptible to infection, yet no adverse effects have been shown against nontargets in field studies. Nematode production is easily accomplished for some species using standard fermentation in tanks up to 150,000 liters. Nematodes do not require specialized application equipment as they are compatible with standard agrochemical equipment.[xiv]

“But wait!” you may say, “if these creatures are such efficient killers then surely they can multiply, spread and kill off everything they touch, even human-beneficial insects.” A fair point, but one that isn’t backed up in practice. The aim of applying commercially available biological control nematodes is in order to overload the natural system and kill many more insects than would be killed by nematodes naturally[xv]. After they are applied, they do indeed destroy their targets very quickly, but once the target is destroyed then there is little for the juvenile worm to mature within and nematode numbers rapidly decline.

So why aren’t nematodes used all over the world, making most types of pesticides redundant? There are three reasons. First, not a lot of widely read research has been carried out on the usefulness of such nematodes; in fact many nematologists still believe that every nematode is a pest[xvi]. Second, although nematode insect parasites were identified as effective controls in the 1930’s, the availability of cheap, effective chemical pesticides in the 1940s caused this research to be largely ignored, and it was not until some chemicals were banned that research started up again[xvii]. Finally, and linking these two together, it is clear from the continued lobbying of powerful companies like BASF, Monsanto and Syngenta, that the chemical industry will not give up without a fight. It is no coincidence that DDT was not widely banned until 20 years after clear evidence of its terrible impacts on wildlife was made public, and that the 2007 European Union REACH legislation – which enforces the control of hundreds of previously uncontrolled chemicals – took ten difficult years to come into force. Industry still calls the shots, even in an age when it is so obvious that natural ecosystems cannot cope with the torrent of chemicals being washed into them day after day.

I may come back to this later.

Moving With The Climate

How fast can a nematode move? One study suggests that 3cm in five hours is a fair guess[xviii]; although there are so many variables that all we can truly say is they move pretty well considering their size. Despite their elegant, sinuous propulsion method, the problems nematodes have in movement are manifold, largely related to their diminutive length. Even in water, something about a millimetre long will experience considerable pressures from all sides, and have to swim through the thick soup of tightly interconnected molecules to make any headway – if you have ever tried to run in the sea then you will understand how it feels. In the soil the problems are multiplied: air gaps have to be traversed, boulder-like grains circumvented and anything like a solid object simply accepted as impassable. Viruses and bacteria can be carried in water flows, or in droplets through the air, but animal vectors are the smart way to travel, whether this be within parasitised insects or the gut of a human. A flying insect, bird or aircraft will lap up distance with ease, meaning that anything able to take advantage of a mobile host is definitely one more rung up the evolutionary ladder. Nematodes are also easily transmitted from one place to another on plants, as they are moved from nursery to farm and on agricultural equipment. The latter is particularly significant. It only requires a farmer to plough a field infected with, for instance, Root Knot Nematode, and then plough an uninfected field with the same plough for the nematode to become ensconced in the next field.[xix]

In terms of climate change, though, speed is not of the essence. The rate of global heating, although significant in its impact on the forces that drive weather and other processes that rely on heat, is slowly creeping across the Earth. Slowly, but inexorably, altering environments as the swath of change moves across the land and the sea. Gradual movement is what nematodes can best take advantage of, and that gradual movement is what is starting to concern farmers. There is a concept used by phenologists (people who study the timescales and cycles of natural events) called Degree Days. A degree day is simply a measure of the amount of time available for an event to occur depending on temperature: one day at one degree above the lowest temperature an organism will breed at is one degree day. Using this system it is possible to predict the lengths of the lifecycles of many organisms, including nematodes, according to the measured air temperature. For example, if a certain nematode requires the temperature to be above 5°C and below 30°C to carry out its lifecycle, four days at a constant 10°C makes twenty degree days.

Using degree days, not only is it possible to work out how long the lifecycle of a nematode will take at different temperatures, but you can also determine if an area of soil is warm enough for the lifecycle to take place at all. The Root Knot Nematode is widely regarded as one of the world’s most destructive pathogens[xx]. If a particular species of root knot nematode needs 1000 degree days to produce an entirely new generation of worms[xxi] in a new crop of potatoes or carrots in a new field, then a one degree average temperature increase could certainly make the difference between a new field being a favourable breeding ground or not, and the difference between a crop being successful or not. One ploughing is enough to distribute a few plants’ worth of nematodes across an entire field; just because nematodes move slowly, doesn’t mean that they can’t spread extraordinarily quickly. If temperatures in a field never drop below the lower threshold for root knot nematode, then the nematode will happily keep multiplying there all the time food is available: impervious, because of sheer numbers, to all but the most toxic applications of pesticide. I’ll leave you to imagine what the impact of increasing temperature on our food supply could be.

A Singularity Of Bananas

Here are some facts about bananas:

1. They grow on the stems of ground-loving plants, not trees.

2. The fruit of the banana plant can be yellow, green, purple or even red.

3. In their natural form, bananas have large seeds.

4. A single variety, “Cavendish”, accounts for the vast majority of the world’s banana trade. It is virtually seedless.

5. Bananas are an analogy for the whole of the industrial economy.

Ok, that last one you won’t find in any text books or scientific journals, but I’m not just making this up on the spot; you may consider society to have gone “bananas” in more ways than one, but even that isn’t what I’m getting at. The simple fact is that the bananas that most of us eat are in deadly peril, and it is likely that the global supply will be largely wiped out within a few years. It was only in the 1950s that the previous reigning variety “Gros Michel” was almost totally destroyed by a fungus called Panama Disease. Gros Michel had many of the characteristics of Cavendish, except it wasn’t resistant to the particular type of fungus that Cavendish is; but that is set to change dramatically. The problem is that every Cavendish plant is genetically identical to the original variety that was brought to the Caribbean from South East Asia in the early 19^th century[xxii], regardless of the small differences in texture, size and colour that derive from different growing methods and climates. In order for genetic variety to occur in plants that reproduce sexually, two sets of chromosomes, one male, one female, have to be combined. Making cuttings doesn’t create genetic variety, and this is basically the reason why family interbreeding amongst humans has been outlawed in most human cultures for centuries, possibly even thousands of years. It is not possible for different sexes to be genetically identical, but if brothers and sisters, or other close relatives breed over a number of generations, then any damaging genetic mutations will remain within the family line, eventually leading to a much higher rate of abnormalities, including poor resistance to disease.

Evolution occurs in order to ensure that a particular species remains hardy enough to continue its line. The Cavendish, and the Gros Michel before it, are perfect examples of what happens when evolution is not allowed to occur. In the 40 years since Gros Michel was almost wiped off the map, the fungus that caused Panama Disease in that plant has evolved so that it can now do the same to Cavendish. In the words of one writer: “the banana is too perfect, lacking the genetic diversity that is key to species health. What can ail one banana can ail all. A fungus or bacterial disease that infects one plantation could march around the globe and destroy millions of bunches, leaving supermarket shelves empty.”[xxiii] Lack of bananas may not cause huge numbers of deaths, but lack of genetic diversity most certainly can:

From 1845 to 1846 Ireland's potato crop consisted of one or two closely related varieties. Both were wiped out by blight. In the ensuing famine, nearly a million people died and more than a million others were forced to emigrate. By 1851 Ireland’s population had diminished by 23 percent. If Irish farmers had been growing many varieties of potatoes with different genetic backgrounds the disaster would never have happened.[xxiv]

You may ask why this is an analogy of the industrial economy. The reason is that throughout the 20^th century and into the 21^st century, money and the possession of material goods have come to dominate the way societies are run, especially in the industrial West. The market economy, which governs the way most commerce and a great deal of politics in the world operates, does not favour diversity – positively discourages it, in fact. The spoils almost always end up going to the individual, company or country that can provide the most of some thing or another – whether that be a raw material, a consumer product, a service or a variety of banana or potato – at the cheapest price, in the shortest time and, often as a result, at the lowest quality. There is no way out of this; it is just the way this type of economic system works: if you want variety (and quality) then you have to operate outside of the market economy.

Of course there are notable exceptions, for instance products that fail strict safety guidelines in one country will not be sold there, but that does not mean they cannot be successful in countries where those guidelines don’t exist. The much-touted sub-$2000 car will, no doubt, be a roaring success in India, its country of manufacture, but can never be sold in Europe, Canada or the USA due to its poor construction. But in the main, big, fast and cheap wins out; so while the Cavendish banana is the type chosen by the largest producers, who effectively have the banana market cornered, then that will be the banana that sits on supermarket shelves, market stalls and in fruit bowls around the world.

You may also ask what all this talk about bananas is doing in a chapter about nematodes. Like almost all types of food crop, bananas are vulnerable to attack by nematodes; and in many countries they can causes losses[xxv] of 30-60 percent – that is the difference between making a living from banana sales, and not being able to afford to grow the crop. Two particular species of nematode, Pratylenchus coffeae and Radopholus similis, exist right across the world, from the Caribbean, to Ecuador, to Central Africa, to the Philippines – in fact everywhere bananas are grown on a commercial basis. There can be little doubt that this vast distribution is the result of a single, genetically identical variety of banana having a virtual monopoly. Even if the new strain of Panama Disease doesn’t finish off the world’s banana crop, then a tiny writhing worm may well do so; a tiny little worm whose relations we hardly notice, but which exist in uncountable numbers in almost every animal, every piece of soil, every plant and all the way down at the bottom of the ocean.

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