as we now call him, is occasionally required--and with no sacrifice of
his principles either--to eat an extra snake to satisfy the curiosity
of some distinguished visitor. Sometimes, too, colubers are plentiful,
and two small ones are not too much for his ten or twelve feet of
appetite. This splendid serpent has rewarded care by remaining in
perfect health, and growing several feet. He was between eight and
nine feet long when he came, and is now not far short of twelve and
proportionately larger in circumference. Sometimes during winter, when
ring-snakes are scarce, "Ophi" is compelled to fast; for he is not
then to be tempted with other food. During the first year of his
residence in the Gardens, the supply was good, and he ate no less than
eighty-two fellow-creatures before the winter was well over. Towards
spring, however, the supply ran short, and only two more remained for
him. He had now fasted two entire weeks, and looked hungry and eager.
The keeper offered him a guinea-pig, at which he took great offence,
raising his hood and hissing angrily for a long while. Eggs he
declined, also a lizard and a rat, in great disgust. In India the
Ophiophagi are said to feed on lizards and fish occasionally, but
_our_ Ophiophagus preferred to fast. At last one of the two
ring-snakes was produced, and Ophio was to be regaled. It was the 31st
of March, 1876, and he had been a denizen of the Gardens just one
year. My note-book informs me that it was a lovely, soft spring day,
and that Ophio was quite lively. He had rejected frogs on his own
account, but in the uncertainty of more ring-snakes arriving, he was
now decoyed into eating half a dozen. Holland contrived that the snake
destined for his dinner should answer the purpose of a feast, and had
allowed it to eat as many frogs as it chose. Like the poor wretch who,
doomed to the gallows, is permitted to fare sumptuously the last
morning of his life, the ring-snake ate three frogs, by which the
Ophiophagus was to derive chief benefit; he, all unconscious of the
cause of his victim's unusual plumpness, swallowed him speedily.
Soon after this Ophio doffed his winter coat entire, and having again
fasted for ten days, was at once rewarded by the last remaining
ring-snake in a similarly plethoric condition, namely, with three more
frogs inside him. Now and then during the winter months the scarcity
of ring-snakes has compelled the sacrifice of some far rarer colubers
to Ophio's cannibal tastes. And yet each year we hear of hundreds of
ring-snakes being ruthlessly killed in country districts, while at
great cost and trouble others are purchased or brought from the
Continent for the Hamadryad's sustenance. Lord Lilford, one of the
Ophidarium's best patrons, sometimes sends presents of game in the
shape of ring-snakes to the Hamadryad.
While watching this snake-eater over his dinner, one is struck with
the remarkable tenacity of life exhibited in the victim, or the slow
action of the venom if poisoned in the first grasp. The Ophiophagus
seizes it anywhere, that is, at whichever part happens to come first,
and then, after holding it quietly for a time, works his jaws up to
the head in the usual hand-over-hand, or "jaw-after-jaw" fashion,
invariably swallowing the snake head first. On one occasion when I
watched attentively, Ophio, having seized a ring-snake by the middle,
held it doggedly still for one quarter of an hour, while the lesser
snake did its very best to work its way out of the jaws, and also to
fetter its captor by twirling itself over his head and coiling round
his neck. This continued while Ophio, with his head and neck raised,
remained motionless, and after the quarter of an hour commenced to
work his jaws up towards the head of the ring snake, which, as more
and more of its own body was free for action, twirled itself about,
and at length coiled its tail round the bit of branch nailed into the
cage.
Persistently, like a sailor making his vessel fast to the windlass,
the ring snake lashed as much of himself as was free round the branch
a foot off, and so pulled and pulled till he looked in danger of
severing himself in two. Meanwhile Ophio, slowly but surely advancing,
caused its head and neck to disappear, grasping tightly with his
venomous jaws, as if he would say, "We'll see who is master." It was a
close tussle, so firmly did the little coluber retain his hold on the
"tree"; but as the upper part of him was gradually drawn into those
unrelaxing jaws, he by degrees gave way, and by and by was gone.
Not far short of an hour was occupied in this meal, during which the
victim showed no signs of being poisoned, nor were his coils round the
stump relaxed in the slightest degree, till Ophio reached the tail.
The ring snake is not a constrictor, yet he thus tied himself round
the tree by the coils of his tail.
One more singular case of tenacity of life must be recorded. A
ring-snake had been caught in the usual way, and the usual struggle
ensued between captor and captive. Coluber, with its head tightly
gripped in the jaws of his enemy, had still all the rest of himself at
liberty and in full activity, and after wriggling a violent protest,
he coiled what was left of himself so closely round the neck of his
persecutor that the latter made little or no progress with his dinner
for a time. He seemed to be deliberating how to proceed next, and
asking, "What is the meaning of this?" then shook his head, lowered it
to the shingle, and tried to rub off the coils. The only result thus
achieved was that the extreme end of Coluber's tail was loosened for a
moment, but only to coil afresh around Ophio's jaws, which
nevertheless slowly and surely advanced.
For nearly an hour the progress was very slow; but when the ring-snake
was nearly all swallowed except a few inches of tail, these became so
tight a muzzle that Ophio in turn was the victim. Shaking his head and
vainly endeavoring to free his jaws of this muzzle, a minute or two
elapsed, during which he seemed to suffer some discomfort, when
suddenly his mouth opened widely, and out crawled Natrix, apparently
none the worse for this temporary entombment. He had turned round when
two or three feet from daylight, and come back to see the world once
more. But it so happened that Ophio closed his jaws in time over the
few inches of tail which still remained between them. Nor did he once
relax his grasp of this, but quickly and patiently began to work his
way up to the head and recommence his meal, and this time with better
success. An hour and a quarter I watched, nor was any evidence of
poison seen, so as to reduce the powers of the bitten snake; for
bitten it must have been in those prolonged and forcible grasps.
[Illustration]
In these conflicts one could but observe a dogged stupidity on the
part of the venomous snake, who, had he but brought coils to his aid,
might have simplified matters so easily. The little Heterodons, and
even the Lacertines, often assist themselves with coils in managing
their prey, though not themselves constrictors; but the venomous ones
have not the slightest notion of helping themselves in this way, as if
confident that in time their venom would do its work.
[Illustration]
WHAT WORMS DO
(FROM THE FORMATION OF VEGETABLE MOULD.)
BY CHARLES DARWIN.
[Illustration]
We now come to treat of a curious and important subject,--namely, the
amount of earth which is brought up by worms from beneath the surface,
and is afterwards spread out more or less completely by the rain and
wind. The amount can be judged of by two methods,--by the rate at
which objects left on the surface are buried, and more accurately by
weighing the quantity brought up within a given time. We will begin
with the first method, as it was first followed.
Near Maer Hall in Staffordshire, quick-lime had been spread, about the
year 1827, thickly over a field of good pasture-land, which had not
since been ploughed. Some square holes were dug in this field in the
beginning of October, 1837, and the sections showed a layer of turf,
formed by the matted roots of the grasses, 1/2 inch in thickness,
beneath which, at a depth of 21/2 inches (or 3 inches from the surface),
a layer of the lime in powder or in small lumps could be distinctly
seen running all round the vertical sides of the holes. The soil
beneath the layer of lime was either gravelly or of a coarse sandy
nature, and differed considerably in appearance from the overlying
dark-coloured fine mould. Coal-cinders had been spread over a part of
this same field either in the year 1833 or 1834; and when the above
holes were dug, that is, after an interval of 3 or 4 years, the
cinders formed a line of black spots round the holes, at a depth of
1 inch beneath the surface, parallel to and above the white layer of
lime. Over another part of this field cinders had been strewed, only
about half a year before, and these either still lay on the surface or
were entangled among the roots of the grasses; and I here saw the
commencement of the burying process, for worm-castings had been heaped
on several of the smaller fragments. After an interval of 43/4 years
this field was re-examined, and now the two layers of lime and cinders
were found almost everywhere at a greater depth than before by nearly
1 inch, we will say by 3/4 of an inch. Therefore, mould to an average
thickness of .22 of an inch had been annually brought up by the worms,
and had been spread over the surface of this field.
Coal-cinders had been strewed over another field, at a date which
could not be positively ascertained, so thickly that they formed
(October, 1837) a layer, 1 inch in thickness at a depth of about
3 inches from the surface. The layer was so continuous that the
overlying dark vegetable mould was connected with the sub-soil of
red clay only by the roots of the grasses; and when these were broken,
the mould and the red clay fell apart. In a third field, on which
coal-cinders and burnt marl had been strewed several times at unknown
dates, holes were dug in 1842; and a layer of cinders could be traced
at a depth of 31/2 inches, beneath which at a depth of 91/2 inches from
the surface there was a line of cinders together with burnt marl. On
the sides of one hole there were two layers of cinders, at 2 and
31/2 inches beneath the surface; and below them at a depth in parts of 91/2,
and in other parts of 101/2 inches there were fragments of burnt marl.
In a fourth field two layers of lime, one above the other could be
distinctly traced, and beneath them a layer of cinders and burnt marl
at a depth of from 10 to 12 inches below the surface.
A piece of waste land was enclosed, drained, ploughed, harrowed, and
thickly covered in the year 1822 with burnt marl and cinders. It was
sowed with grass seeds, and now supports a tolerably good but coarse
pasture. Holes were dug in this field in 1837, or 15 years after its
reclamation, and we see in the accompanying diagram (Fig. 1) reduced
to half of the natural scale, that the turf was 1/2 inch thick, beneath
which there was a layer of vegetable mould 21/2 inches thick. This layer
did not contain fragments of any kind; but beneath it there was a
layer of mould, 11/2 inch in thickness, full of fragments of burnt marl,
conspicuous from their red color, one of which near the bottom was an
inch in length; and other fragments of coal-cinders together with a
few white quartz pebbles. Beneath this layer and at a depth of
41/2 inches from the surface, the original black, peaty, sandy soil with a
few quartz pebbles was encountered. Here, therefore, the fragments of
burnt marl and cinders had been covered in the course of 15 years by a
layer of fine vegetable mould, only 21/2 inches in thickness, excluding
the turf. Six and a half years subsequently this field was
re-examined, and the fragments were now found at from 4 to 5 inches
beneath the surface. So that in this interval of 61/2 years, about
11/2 inch of mould had been added to the superficial layer. I am surprised
that a greater quantity had not been brought up during the whole
211/2 years, for in the closely underlying black, peaty soil there were many
worms. It is, however, probable that formerly, whilst the land
remained poor, worms were scanty; and the mould would then have
accumulated slowly. The average annual increase of thickness for the
whole period is .19 of an inch.
[Illustration: FIG. 1.
Section of the vegetable mould in a field, drained and reclaimed
fifteen years previously; a, turf; b, vegetable mould without
any stones; c, mould with fragments of burnt marl, coal cinders,
and pebbles; d, sub-soil of black, peaty sand with quartz
pebbles.]
Two other cases are worth recording. In the spring of 1835 a field,
which had long existed as poor pasture, and was so swampy that it
trembled slightly when stamped on, was thickly covered with red sand
so that the whole surface appeared at first bright red. When holes
were dug in this field after an interval of about 21/2 years, the sand
formed a layer at a depth of 3/4 inch beneath the surface. In 1842
(i.e., seven years after the sand had been laid on) fresh holes were
dug, and now the red sand formed a distinct layer, 2 inches beneath
the surface, or 11/2 inch beneath the turf; so that on an average
.21 inches of mould had been annually brought to the surface. Immediately
beneath the layer of red sand the original sub-stratum of black, sandy
peat extended.
A grass field, likewise not far from Maer Hall, had formerly been
thickly covered with marl, and was then left for several years as
pasture; it was afterwards ploughed. A friend had three trenches dug
in this field 28 years after the application of the marl, and a layer
of the marl fragments could be traced at a depth, carefully
measured, of 12 inches in some parts, and of 14 inches in other parts.
This difference in depth depended on the layer being horizontal,
whilst the surface consisted of ridges and furrows from the field
having been ploughed. The tenant assured me that it had never been
turned up to a greater depth than from 6 to 8 inches; and as the
fragments formed an unbroken horizontal layer from 12 to 14 inches
beneath the surface, these must have been buried by the worms whilst
the land was in pasture before it was ploughed, for otherwise they
would have been indiscriminately scattered by the plough throughout
the whole thickness of the soil. Four and a half years afterwards I
had three holes dug in this field, in which potatoes had been lately
planted, and the layer of marl fragments was now found 13 inches
beneath the bottoms of the furrows, and therefore probably 15 inches
beneath the general level of the field. It should, however, be
observed that the thickness of the blackish, sandy soil, which had
been thrown up by the worms above the marl fragments in the course of
321/2 years, would have measured less than 15 inches, if the field had
always remained as pasture, for the soil would in this case have been
much more compact. The fragments of marl almost rested on an
undisturbed sub-stratum of white sand with quartz pebbles; and as this
would be little attractive to worms, the mould would hereafter be very
slowly increased by their action.
We will now give some cases of the action of worms, on land differing
widely from the dry, sandy, or the swampy pasture just described. The
chalk formation extends all round my house in Kent; and its surface,
from having been exposed during an immense period to the dissolving
action of rain-water, is extremely irregular, being abruptly festooned
and penetrated by many deep, well-like cavities. During the
dissolution of the chalk the insoluble matter, including a vast number
of unrolled flints of all sizes, has been left on the surface and
forms a bed of stiff red clay, full of flints, and generally from 6 to
14 feet in thickness. Over the red clay, wherever the land has long
remained as pasture, there is a layer a few inches in thickness of
dark-coloured vegetable mould.
A quantity of broken chalk was spread, on December 20, 1842, over a
part of a field near my house, which had existed as pasture certainly
for 30, probably for twice or thrice as many, years. The chalk was
laid on the land for the sake of observing at some future period to
what depth it would become buried. At the end of November, 1871, that
is, after an interval of twenty-nine years, a trench was dug across
this part of the field; and a line of white nodules could be traced on
both sides of the trench, at a depth of 7 inches from the surface. The
mould, therefore (excluding the turf), had here been thrown up at an
average rate of .22 inches per year. Beneath the line of chalk nodules
there was in parts hardly any fine earth free of flints, while in
other parts there was a layer 21/4 inches in thickness. In this latter
case the mould was altogether 91/4 inches thick; and in one such spot a
nodule of chalk and a smooth flint pebble, both of which must have
been left at some former time on the surface, were found at this
depth. At from 11 to 12 inches beneath the surface, the undisturbed
reddish clay, full of flints, extended. The appearance of the above
nodules of chalk surprised me much at first, as they closely resembled
water-worn pebbles, whereas the freshly-broken fragments had been
angular. But on examining the nodules with a lens, they no longer
appeared water-worn, for their surfaces were pitted through unequal
corrosion, and minute, sharp points, formed of broken fossil shells,
projected from them. It was evident that the corners of the original
fragments of chalk had been wholly dissolved, from presenting a large
surface to the carbonic acid dissolved in the rain-water and to that
generated in soil containing vegetable matter, as well as the
humus-acids. The projecting corners would also, relatively to the
other parts, have been embraced by a larger number of living rootlets;
and these have the power of even attacking marble, as Sachs has shown.
Thus, in the course of twenty-nine years, buried angular fragments of
chalk had been converted into well-rounded nodules.
Another part of this same field was mossy, and as it was thought that
sifted coal-cinders would improve the pasture, a thick layer was
spread over this part either in 1842 or 1843, and another layer some
years afterwards. In 1871 a trench was here dug, and many cinders lay
in a line at a depth of 7 inches beneath the surface, with another
line at a depth of 51/2 inches parallel to the one beneath. In another
part of this field, which had formerly existed as a separate one, and
which it was believed had been pasture-land for more than a century,
trenches were dug to see how thick the vegetable mould was. By chance
the first trench was made at a spot where at some former period,
certainly more than forty years before, a large hole had been filled
up with coarse, red clay, flints, fragments of chalk, and gravel; and
here the fine vegetable mould was only from 4 1/8 to 4 3/8 inches in
thickness. In another and undisturbed place, the mould varied much in
thickness, namely, from 61/2 to 81/2 inches; beneath which a few small
fragments of brick were found in one place. From these several cases,
it would appear, that during the last 29 years mould has been heaped
on the surface at an average annual rate of from .2 to .22 of an
inch. But in this district when a ploughed field is first laid down in
grass, the mould accumulates at a much slower rate. The rate, also,
must become very much slower after a bed of mould, several inches in
thickness, has been formed; for the worms then live chiefly near the
surface, and burrow down to a greater depth so as to bring up fresh
earth from below, only during the winter, when the weather is very
cold (at which time worms were found in this field at a depth of
26 inches), and during summer, when the weather is very dry.
A field which adjoins the one just described, slopes in one part
rather steeply (viz., at from 10 deg. to 15 deg.); this part was last ploughed
in 1841, was then harrowed and left to become pasture-land. For
several years it was clothed with an extremely scant vegetation, and
was so thickly covered with small and large flints (some of them half
as large as a child's head) that the field was always called by my
sons "the stony field." When they ran down the slope the stones
clattered together. I remember doubting whether I should live to see
these larger flints covered with vegetable mould and turf. But the
smaller stones disappeared before many years had elapsed, as did every
one of the larger ones after a time; so that after thirty years (1871)
a horse could gallop over the compact turf from one end of the field
to the other, and not strike a single stone with his shoes. To anyone
who remembered the appearance of the field in 1842, the transformation
was wonderful. This was certainly the work of the worms, for though
castings were not frequent for several years, yet some were thrown up
month after month, and these gradually increased in numbers as the
pasture improved. In the year 1871 a trench was dug on the above
slope, and the blades of grass were cut off close to the roots, so
that the thickness of the turf and of the vegetable mould could be
measured accurately. The turf was rather less than half an inch, and
the mould, which did not contain any stones, 21/2 inches in thickness.
Beneath this lay coarse, clayey earth full of flints, like that in any
of the neighboring ploughed fields. This coarse earth easily fell
apart from the overlying mould when a split was lifted up. The average
rate of accumulation of the mould during the whole thirty years was
only .083 inch per year (i.e., nearly one inch in twelve years); but
the rate must have been much slower at first, and afterwards
considerably quicker.
The transformation in the appearance of this field, which had been
effected beneath my eyes, was afterwards rendered the more striking,
when I examined in Knole Park a dense forest of lofty beech-trees,
beneath which nothing grew. Here the ground was thickly strewed with
large, naked stones, and worm-castings were almost wholly absent.
Obscure lines and irregularities on the surface indicated that the
land had been cultivated some centuries ago. It is probable that a
thick wood of young beech-trees sprung up so quickly, that time enough
was not allowed for worms to cover up the stone with their castings,
before the site became unfitted for their existence. Anyhow, the
contrast between the state of the now miscalled "stony field," well
stocked with worms, and the present state of the ground beneath the
old beech-trees in Knole Park, where worms appeared to be absent, was
striking.
A narrow path running across part of my lawn was paved in 1843 with
small flag-stones, set edgeways; but worms threw up many castings, and
weeds grew thickly between them. During several years the path was
weeded and swept; but ultimately the weeds and worms prevailed, and
the gardener ceased to sweep, merely moving off the weeds, as often as
the lawn was mowed. The path soon became almost covered up, and after
several years no trace of it was left. On removing, in 1877, the thin
overlaying layer of turf, the small flag-stones, all in their proper
places, were found covered by an inch of fine mould.
Two recently published accounts of substances strewed on the surface
of pasture-land, having become buried through the action of worms, may
be here noticed. The Rev. H. C. Key had a ditch cut in a field, over
which coal-ashes had been spread, as it was believed, 18 years before,
and on the clean-cut perpendicular sides of the ditch, at a depth of
at least 7 inches, there could be seen, for a length of 60 yards, "a
distinct, very even, narrow line of coal-ashes, mixed with small coal,
perfectly parallel with the top-sward." This parallelism and the
length of the section gives interest to the case. Secondly, Mr. Dancer
states that crushed bones had been thickly strewed over a field, and
"some years afterwards" these were found "several inches below the
surface, at a uniform depth." Worms appear to act in the same manner
in New Zealand as in Europe; for Professor J. von Haast has described
a section near the coast, consisting of mica-schist, "covered by 5 or
6 feet of loess, above which about 12 inches of vegetable soil had
accumulated." Between the loess and the mould there was a layer from 3
to 6 inches in thickness, consisting of "cores, implements, flakes,
and chips, all manufactured from hard basaltic rock." It is,
therefore, probable, that the aborigines, at some former period, had
left these objects on the surface, and that they had afterwards been
slowly covered up by the castings of worms.
Farmers in England are well aware that objects of all kinds, left on
the surface of pasture-lands, after a time disappear, or, as they say,
work themselves downwards. How powdered lime, cinders, and heavy
stones, can work down, and at the same rate, through the matted roots
of a grass-covered surface, is a question which has probably never
occurred to them.