Talking ****

Talking ****

"What falls from a cow and rings like a bell? …

Dunnnngggg!"

                                       Spike Milligan

For such repellent subject matter, ordure is surprisingly interesting stuff.  Perhaps this should come as no surprise; it is after all a major phase in the biological cycle of energy and material, and is a vital resource to many animals and plants.  That sounds simple, but all sorts of questions arise.  For one thing, why should it occur in so many forms: uncreative slugs and jobbies, such as those of dogs, baboons and porcupines; sloppy pads like those of cattle; hard, neat pellets like those of rats; clustered pills like those of horses or goats; or elaborately sculpted like those of large caterpillars?  Some are smooth in texture, some granular, some fibrous, and in some you can see seeds or visible parasites.  Most of us don’t give the matter a thought; it is just the way things are, and not things we care to investigate intimately.

But those shapes and textures are not random.  They reflect the foods, ecologies and gut shapes of the animals.  The usual scheme of digestion is: break up the food to expose its nourishing bits; wet it thoroughly so that your enzymes can work on well separated substrate molecules; and treat it to a series of digestive juices that give special treatment to different components in turn.  Then extract what nutrients you can from the result, and finally extract water so that you can void the residue without waste or fouling.  

Of course there are exceptions and elaborations almost beyond imagining.  For instance, beasts that fly have little selective pressure to develop house training.  To them the concept of crying gardyloo would be alien.  Pigeons and seagulls are famous spotters and bats are hardly more considerate, passing what they no longer want, without considering where they may be, or what may be passing beneath. 

Not surprisingly, such facts are exploited by plants that disperse seeds by the oral-anal route.  Mistletoes are important examples, because in that way some of their sticky seeds land on twigs.  Some plants depend absolutely on the creatures that eat their fruit and disperse the seeds in the manure.  Various plants need the dispersal, the preparation of the seed case for germination, and the nutrition that accompanies the seed when it is voided.  Such softening of the seed or its hard shell can make the manure of large animals such as elephants very attractive to rodents or birds that eagerly pick out the tasty bits whenever their benefactors have been eating the right stuff.

 

Amazingly, since I wrote the foregoing, it has turned out that at least one insect, one of the stick insects, can disseminate its eggs in the same way as some kinds of hard plant seeds; when the mother is swallowed by a bird, mature eggs inside her body pass through the bird's gut, and hatch from the droppings. This could work for insectivorous birds, though seed-eating birds with abrasive gizzards probably would digest the eggs, hard-shelled though they may be. Still, convergent evolution, as we see in this example of insect eggs and the hard seeds of plants, is repeatedly breathtaking.

Flying animals with no shortage of water are likely to void their wastes in dismissive squirts.  Many birds of prey do so, and the only care they take is not to get the stuff on themselves.  Eagles have been known to electrocute themselves by sitting on a high-voltage wire and closing the circuit when their jet of excrement hits another wire with such a squirt. 

However, not many animals can afford to waste water like that, so the trend is to retain the excreta in the last part of the gut before unloading, and to absorb moisture from those wastes, holding onto them till they become firmer and drier.  As a result of our evolutionary history, we mammals excrete our unwanted nitrogen in the form of urea dissolved wastefully in water, keeping it separate from our gut contents, and that causes us all sorts of difficulties, ranging from constipation to kidney stones. 

 

In contrast, reptiles and birds convert waste nitrogen from their metabolism into uric acid. Uric acid is an insoluble powder that we can see as lumps of white paste attached to their dark droppings. That saves a lot of water, and avoids the formation of kidney stones and similar horrors. 

 

A common sign of ill health is for an animal to foul itself because its droppings pass through while still too runny to cope with cleanly.  For most animals it is important to get away from their excreta as cleanly as possible, if not for the sake of hygiene, then at least to avoid attracting predators.  

 

To survive in filth, animals must develop a high degree of resistance to infection.  One strategy is to secrete substances that discourage many microbes, but to develop a relationship with crowded populations of yeasts and the like that outcompete most harmful germs.  The resistance of such mucky species to bad husbandry may make them convenient to keep in captivity, while clean, mobile species can be a challenge to keep healthy.  But there are counterexamples. For instance, capybara and a surprising number of other animals will insist on defecating in their water, and unless there is a good supply of unfouled water for drinking, trouble simply must follow sooner or later.

When animals are tied down to a small area and still need to keep clean for safety and for health, they have to develop suitable housekeeping practices. Some birds rely on ants and other scavengers to char for them, some remove their nestlings’ droppings, some eat those droppings, and some  some animals bury their manure. 

 

Some animals such as mother cats will lick the bellies of their still-blind kittens to stimulate their urination and defecation, which they swallow. This both improves their internal economy during the period in which they cannot be away from the nest for long, and improves the nest hygiene. It also may improve security by reducing smells that might attract predators to the nest.  

For mobile animals such as savannah-grazing antelope in migration, the question of when and where to defecate is no problem: they drop their souvenirs and move on with no more concept of house training than birds.  Some savanna animals however, when not on the move, seem to concentrate their droppings in piles, either thereby maintaining social cohesion by marking the spots with their own group smell, or improving the quality of their local forage plants with their own fertilisers. 

 

Creatures tied to a stationary territory or a nest however, either must put up with their own dung or apply sanitary measures in the interests of hygiene or safety. Those that pig it often make a virtue of being so revolting that competitors and predators stay away; hoopoe nests are notoriously foul, and many a moth larva has survived in a bitten apple flung away by a human too finicky to profit from a tiny windfall of rich protein!  Fruit-eating monkeys in contrast, often seek out inhabited fruits exactly because they relish the proteins, lipids, and vitamins in the insects that they contain.

 

Other creatures, such as fly larvae that live in flesh or fruit or hard plant tissue, use their own secretions and excretions to kill and pre-digest host tissue, and to enrich it with fungi that make it more nutritious.  This can be a matter of great concern in our economy and ecology; for example, with few exceptions such as the stems of sago palms, wood is generally a very poor diet, so some wood-boring insects carry spores of special fungi that predigest the wood and make it digestible. The fungi then may go on to kill the host tree, so that say, the tiny Polyphagous Shot Hole Borers, though an entire infestation might consume only a few grams of wood, may kill an entire tree massing tonnes; such beetles may destroy whole forests with their fungus-laden shit. Often, even trees that can shrug off the infestation are stunted, or their wood is disfigured and damaged. 

 

Insects such as the Lesser Aloe Weevil, that infest some valuable succulent plants, destroy plants wastefully in the same way. 

 

Even animals that eat foods more nourishing than wood, and do not need the assistance of their own dung to digest it, may rely on their own droppings for shelter or self-defence; for example some leaf beetles in the family Chrysomelidae, carry packs of their own smelly, poisonous ordure on their backs. That does not deter the parasitoid wasps that kill them, but not many birds and lizards will tolerate that offensive muck.   

 

Consider the following photograph of a Cape chameleon; it is defecating while perching on a twig. It holds on with its tail and fore-feet, but lets go with one hind foot, positioning its cloaca away from the perch. The turd then falls away cleanly. Incidentally, you can see a scrap of uric acid at the tip. 

 

 

 

On the one hand, to drop the turd is a pity, because, if it stuck to the twig, it could attract tasty flies, but what is more urgently important is that one of the chameleon's main predators is the boomslang, Dispholidus typus, and for a chameleon to leave dung on its perch where the snake could detect it and assess its freshness, would be a bad selective strategy.

 

I also have known a charming sedentary Pamphagid grasshopper who would extrude a longish, hard dropping most of the way out, then nonchalantly raise one hind leg and neatly flick it several metres away.  The kick had sufficient force to send the projectile ricocheting about the laboratory (much to my puzzlement before I caught her at it).  

 

In a remarkable parallel, at least one species of Hesperid caterpillar which lives in a rolled up leaf, constructs a dropping inside its hind gut.  Its anus has a shutter with a catch.  Over a period of some twenty minutes blood pressure builds up till the shutter pops and the pellet shoots out to land somewhere safely remote.  Actual experiment has demonstrated that many parasitoids actively seek out droppings of caterpillars and similar hosts or prey, as part of their strategy of finding the hosts themselves.

Such a build-up of pressure may sound like the constipatee’s nightmare, but there is worse.  The larvae of many Hymenoptera that live on concentrated food with little waste, such as bees and many wasps, have a sealed anus and simply concentrate their wastes in a visible dark blob in the hind gut, till they are about to pupate.  Then they let the lot go at once.  

  

Some species then roll about in their cells and form part of the slush of their own muck into a neat, parchmenty brown-paper cocoon, inside which they shed their skin and pupate.  The pupa is a delicate structure that at first looks like sculpted crystal, and on seeing it in its elegant casket, it may be difficult to associate it with such sordid origins.

Mind you, that cocoon of dried ordure seems to be a very special protection against microbes, mites and other threats to the vulnerable pupa. Dried dung of various sorts can be surprisingly sanitary; cattle dung, suitably prepared, is a component of earthen floors in various countries to this day, including parts of India and Africa. 

 

In South Africa even well-to-do, respectable rural Boer families commonly lived on firm, odourless misvloere (literally "dung floors") till well into the 20th century. But don't get the wrong idea; you don't get a decent misvloer just by creating an indoor midden — it must be the right stuff in the right mix, properly prepared, and the result is to be swept, maintained, and respected. Damage the floor thoughtlessly and the lady of the house would be no better pleased than the owner of a modern wooden floor gouged by stiletto heels or the like.

By and large, animals with a rich, digestible, or at least plentiful diet, tend to be the ones with the prosaically shaped turds.  I cannot think of a single mammalian carnivore that voids anything but lumps or splashes.  This reflects the simple, tubular shape of the large gut when it has little to do but extract water from a stew of unwanted meat residues.  

 

Simple-shaped turds from herbivores such as browsing black rhino, tend to be full of undigested bits that a more sophisticated digestion for a more digestible diet would have reduced to anonymous slush.  

Paradoxically, many poorly digested turds are particularly rich in wasted food and often they are very popular snacks for species equipped to deal with them. When fresh, they do not usually attract the original owners, which makes sense; the very reason they were voided, was that they contained more unwanted material than reward, and probably a batch of poisons and pathogens into the bargain, that the owner could poorly afford to tolerate or utilise.  Therefore, for many animals the manure of one’s own species is best treated as revolting, or at best as a social signal, to be sniffed, but not to be eaten.  

 

In contrast the manure of other species does not always give the right chemical signals, and animals may react more strongly to the attractants than to the repellents.  For instance, hyenas seem to feed avidly on the fresh scats of jackals and of hunting dogs, and hunting dogs on at least those of jackals; and many domestic dogs, if they are kept on a healthily austere diet (which implies that they are always hungry) will eagerly snap up human, cat, or rabbit droppings, sometimes even dog droppings that have weathered into something like anonymity. 

If there are not too many serious parasites in circulation, such coprophagy does no harm, and I suspect that it may be an important route for transmitting bacteriophages that control intestinal bacteria. In this connection you might find it interesting think about the values (and risks) of fecal transplants in dealing with persistent colitis or Clostridium infection in humans. 

 

In many animals coprophagy also can be a vital supplement to an unbalanced diet.  I have read that when the rabbit population in Britain was first reduced to a fraction by myxomatosis, there were many deaths among sheep dogs that no doubt had been fed poorly and hitherto had supplemented their diet with bunny pills. 

Those of us with a taste for pongy cheese such as Limburger, are in no position to raise our noses. Robertson Davies has one of his characters say: "We'll top off with lots and lots of cheese; the goatiest and messiest you have, because I like my cheese opinionated." Psychologists regard such tastes as related to coprophagia: dung-eating — I may not agree with their Freudian interpretations of such activities, but I certainly accept that the association of tastes is persuasive. And not to humans alone.

For example, rabbits in turn, do not have a rich diet in the wild, and unlike cattle they do not have a rumen in which to digest plant fibre efficiently.  Their solution is an interesting demonstration of the versatility of evolution.  Like some rodents (which by the way rabbits are not; they are lagomorphs) that eat a lot of fibrous vegetable matter, rabbits void some of their faeces prematurely as special soft pellets in which microbes have had free rein to grow and digest stubborn fibres.  The rabbits  then eat such pellets as they emerge.  From these pre-digested portions they pick up newly-released nutrients and digest most of the microbes into the bargain.  It is an important source of vitamins as well as harnessing extra digestive power.  

 

If human vegans took their principles to the logical conclusion and adopted this rabbit habit, they could do without vitamin B12 supplements.  But Vegans are not rabid about logic, or consistency of logic. 

Coprophagy is the closest lagomorphine approach to the hare chewing the cud, as referred to in the bible. (Hares, like rabbits, are not rodents but members of the Lagomorpha.)   But it seems that the behaviour depends on a taste for certain faecal components, so rabbits will also eat the scats of some other species.  Keep rabbits in a grassy enclosure with cats, and you will have very little cat manure to clean up.  The rabbits scoff it as a supplement to the grass.  It seems to be a good supplement too, rich in phosphates, nitrogen and other minerals, and energy-rich material to boot.  This is hardly surprising, considering the price of cat food nowadays! 

Unlike dogs, the cats don’t return the compliment.  Cats are specialist carnivores, and accordingly they leave coprophilia to dogs and similarly inferior species. 

Nor are these instances of coprophagy unusual; clean chicken manure is an excellent supplement to coarse, low-quality fodder for cattle.  Rumen flora love it and so do the cows.  Suitably sterilised and powdered, poultry manure actually gets incorporated deliberately into some cattle rations nowadays.  Given the opportunity, free range cows are not so fussy; they don't demand treated droppings and they wolf down whatever they can get, generally without obvious ill effects.  

 

Similarly, in the wild, starving elephants will eat weathered elephant droppings, and baby elephants eat such droppings freely anyway; it is their way of picking up the gut microbes that they need for digesting the coarse plant food that elephants eat so much of.

Weathered carnivore droppings usually don’t last long in the wild either; herbivores, including tortoises, know better than to waste a good source of calcium and other minerals.   

 

Farmers have long offered the equivalent of such resources plus salt licks, by forming mineral and energy supplements into blocks for cattle to lick or nibble.  Commercial production of such blocks is big business.

Another example of where droppings are valued sources of minerals is in some forms of "puddling" by butterflies. Butterflies seem so fairy-pure that many people are shocked to find that many species of butterflies not only will suck at juices and fermenting fluids, but also at mud and — wait for it — dung. This habit is known as puddling. It is very important, especially in regions where there is a deficiency of certain mineral salts, in particular sodium, which is practically absent from most plant foods.   

So far we have largely discussed the manure of animals with simply shaped guts, or with a blind gut or caecum where the small gut meets the large bowel or colon.  At the blind end of the caecum, the appendix is attached. Up to the caecum, most things that happen to the food do not show in the manure, though there are special exceptions. For instance the way fibre has been chewed or components have been dissolved will show in the manure of eaters of coarse plant foods. Black rhino for example are browsers and they have teeth specially adapted to the shearing of the twigs that they eat. The sheared twigs are obvious in the dung. 

What comes after digestion in the small gut, and the caecum, and the start of the colon, the large gut, is the process that shapes the output in preparing the dung for disposal.  Dissect an animal and you see that only the large gut gathers the mush into lumps. There its colour darkens as the microbes work on the bile pigments, and the slush becomes concentrated and solidifies as the water gets extracted.  Light-coloured stools may have many causes, but they usually mean that the stuff has passed through too fast for bacterial darkening, perhaps because of diarrhoea or a sudden glut of food. 

In this process too, the shapes of the turds begin to make sense.  Guts such as those of humans or dogs are more or less tubular and any scats that harden in there take up that shape, or get shaped that way during extrusion.   

 

On the other hand, food that is rich in fibre, especially if the animal has no rumen, or if the fibre is too challenging for the rumen, has to be elaborately extracted in the colon.  Perissodactyla and Lagomorpha, respectively the orders of horses and of rabbits, are examples.  They digest and absorb what they can in the stomach and small gut, then pass the rest, not into the colon, but into the relatively huge caecum.  

 

Humans are adapted to a diet far lower in fibre, so our caecum is hardly more than a junction box with the appendix attached.  Our appendix is mainly a structure, not for digestion, but for exposing lymph nodes to gut microbes, so that our immune system may be prepared to deal with anything that our alimentary lifestyle exposes us to. A healthy, functional appendix also can store populations of our own personal gut microbes and bacteriophages (our "gut flora", as they imaginatively are known). Those populations enable us to repopulate our large gut after diarrhoea or a course of antibiotics. 

Non-ruminant eaters of fibrous plant matter however, are heavily reliant on the caecum itself for digestion of the refractory material in their food.  It is a good system, and most ruminants have well-developed and busy caeca too, but the most imposing specimens where all the serious work gets done, are found in the likes of horses and rhino.   

 

Ruminants like cattle, goats, and antelope deal with fibre the other way round, and though they also have large caeca, you can’t beat the rumen for fermentation, so their caeca are relatively smaller than those of horses.  The rumen stores the crude food till it is predigested, or at least softened.  That food  then comes back up to be chewed properly and goes down again to be filtered and passed through to the stomach and small gut for normal processing. 

Heavier reliance on caecal digestion means that in horses and hares the colon has to absorb many more nutrients as well as water and salts, and it cannot do this as effectively as the small gut.  Still, needs must, so the more important the caecum, the more elaborate the colon.  Humans have lightly segmented colons, but plant eaters, especially those that rely on caecal digestion, have the colon segments sacculated, extended sideways into fancy compartments in which the food is collected and squeezed and sucked dry by the increased absorptive area of the gut walls.   

 

After due exhaustion, the food forms not just pellets, but clusters that reflect the shape of the final chambers of the colon, as seen in dissection.  You can see this clearly in the shape of say, fresh horse manure or the manure of some species of antelope. 

One also can see a great deal in the form of smaller animals’ droppings.  Sucking bugs such as aphids live on diluted plant juices and have to get rid of large quantities of water and sugar.  This they turn to good account by excreting it as the so-called honeydew that attracts ants.  The ants protect the aphids and in some cases care for them, even building shelters.   

 

The care of an ant however, especially some species, is an insecure thing, and I have seen ants carrying away cut-up aphids where I had relied on them to protect my aphid cultures. 

Caterpillars usually feed on fibrous foods and they live fast and furiously, so they cannot afford the elaborate, leisurely digestion process of the cow, so they eat fast, absorb what they can, and compress the rest into dry pellets for excretion.  The absorption is vital for such small animals that cannot afford to lose much water, and many species have far more elaborately sculpted hind-gut linings than any horse.  Their droppings are practically works of art, and they may be more spectacular than their creators.  Large caterpillars of many species of emperor moths or hawk moths are very impressively camouflaged and often I have found a brood of them only when I first noticed their droppings under the food plant. 

 

There always are more aspects to excreta and effluvia than one might expect. Many species use theirs to mark boundaries, either of their own territories, or of the pack. 

 

Again, I have read of the application of fresh cow dung to gangrenous wounds. This has been known to work miracles, either in pre-antibiotic days, or when the gangrene is caused by Clostridum strains resistant to antibiotics. Here again I suspect the effect is caused by bacteriophages rather than natural antibiotics. 

Don’t talk **** people say?  But, like evolution, **** pervades biology; and it pervades everyday life.  Ignore it, however fastidiously, in any relevant context, and you eviscerate the subject.  I have known educated, otherwise  healthy, people to die unappetisingly of complications of fistulas of the colon, for not attending to elementary gut health; not quack medicine, mind you, nor obsessing on every day's production, texture and colour, just maintaining a balanced diet, and keeping regular. You don’t have to like the stuff to find that tracing the topic of shit leads you into everything from nutrition, through behaviour, economy, communication, competition, conflict, and epidemiology to anatomy.    

 

At mealtimes though, if tactlessly indulged in, it is not a topic that enhances one's popularity.  

 

Still, biology is unbalanced without images of the neatly packaged droppings of nestlings in the beaks of mother birds, or of the enthusiasm of huge dung beetles circling in to mounds of fresh elephant dung, or indeed the vile-smelling ordure that some snakes will smear on you if you handle them. 

 

Talking shit might not be an obvious conversational opening for a non-politician, but, having once started, some of us find it hard to stop. We are torn between the need to speak of it and to avoid being indelicate; that might be part of the reason for all the words we use to achieve rhetorical effects of coarseness, archness, anger, maturity or shock. 

 

In illustration of that thought, consider the book: "The Rebel Angels" by Robertson Davies, whose works I enjoy and admire. The following passage, though a minor item in the book, and edited lightly to fit the context, struck me as characteristically penetrating -- and entertaining :

I walked on..., thinking about faeces. What a lot we had found out about the prehistoric past from the study of fossilized dung of long-vanished animals. A miraculous thing, really; a recovery of the past from what was carelessly rejected. And in the Middle Ages, how concerned people who lived close to the world of nature were with the faeces of animals. And what a variety of names they had for them: the Crotels of a Hare, the Friants of a Boar, the Spraints of an Otter, the Werderobe of a Badger, the Waggying of a Fox, the Fumets of a Deer. Surely there might be some words for the material ... better than shit? What about the Problems of a President, the Backward Passes of a Footballer, the Deferrals of a Dean, the Odd Volumes of a Librarian, the Footnotes of a Ph.D., the Low Grades of a Freshman, the Anxieties of an Untenured Professor? As for myself, a man of the cloth, might it not appropriately be called the Collect for the Day? Musing in this frivolous strain I went to bed.