ON THE PRESERVATION OF WOODEN BRIDGES, JETTIES, PILES, HARBOUR WORKS,
ETC., FROM THE RAVAGES OF THE TEREDO NAVALIS AND OTHER SEA-WORMS.
“Perforated sore
And drilled in holes, the solid oak is found
By worms voracious, eaten through and through.”
SIR JOHN BARROW.
As the destruction of timber by fungi has been called the _vegetable_
rot, it may not be inappropriate to term the destruction of wood by
various worms and insects, the _animal_ rot.
We have _four natural enemies_ to deal with: 1st, the _dry rot_, that
attacks our houses, &c.; 2nd, the _worms_, or boring animals, which
destroy our ships and harbours; 3rd, the _rust_, that eats our iron; and
4th, the _moisture and gases_, that destroy our stone.
There are three classes of destructive insects which prey upon
timber trees, founded upon the manner in which they carry on their
operations--viz. those which feed upon the leaves and tender shoots;
those which feed upon the bark and the albumen; and those which feed upon
the heart-wood.
It is to be observed that some of the insects which feed upon the heart
of wood do not cease their ravages upon the removal of the tree; but
that, on the contrary, the _Cossus syrex_, of our indigenous fauna, and
the larvæ of the _Callidium bajutum_, which are often found in imported
timber, continue to devour the wood long after it has been inserted in
buildings. There seem to be very few means of defence against this class
of destructive agents; and very few trustworthy indications of their
existence, or of the extent of the ravages they have committed, are to
be discovered externally; and it thus frequently happens that a sound,
hearty-looking stick of timber may be so seriously bored by these insects
as to be of comparatively little value for building purposes of any
description. The soft and tender woods, and such as are of a saccharine
nature in their juices, are the most liable to be assailed by worms;
those which are bitter are generally, if not invariably, exempt; it is
obvious, therefore, that those palatable juices, which are so conducive
to their production and propagation, should be got rid of by thorough
seasoning, and, if further precaution be necessary, that the infusion of
some bitter decoction into the pores of the wood will be an effectual
preventive; and for which those woods that are of a regular grain afford
sufficient facilities. Ash, if felled when abounding in sap, is very
subject to worms; beech, under similar circumstances, is also liable to
their attacks; likewise alder and birch; in these woods water seasoning
is sometimes found to be a good preventive; the sapwood of oak is also
thus improved; the silver fir is subject to them; the sycamore is rather
so; alder is said when dry to be very susceptible of engendering them;
the cedar, walnut, plane, cypress, and mahogany are examples of woods
which discourage their advances. It has been stated that Robert Stevenson
(not the son of the “Father of Railways”), of Edinburgh, at Bell Rock
Lighthouse (of which he was engineer), between 1814 and 1843, found that
greenheart wood, beef wood, and bullet tree were not perforated by the
_Teredo navalis_, and teak but slightly so. Later experiments show that
the “jarrah” of the East, also, is not attacked. Lignum vitæ is said to
be exempt. The cost of these woods prevents their general use.
In 1810, Stevenson first noticed the _teredo_ in piles, and specimens
of the creatures in wood were sent to Dr. Leach, of the British Museum,
in 1811, who examined them, and noticed their peculiarities. Stevenson,
settled on Bell Rock during many years (like a new Robinson Crusoe), was
enabled to watch the injuries done to the piles by the _teredo_. With
piles which had been subjected to Kyan’s process before immersion, the
wood was attacked at the end of the twenty-eighth month, and was entirely
destroyed in the seventh month of the fifth year. With Payne’s, it lasted
a year longer.
We can give the names of those who have given much time and attention
to this subject. At the bottom of this page a list of works of
reference[16] will be found useful. Messrs. Stevenson (engineer of Bell
Rock Lighthouse), Harting (Member of the Academy of Sciences of the
Pays-Bas), de Quatrafages, Deshayes, Caillaut, Hancock, Dagneau, de
Gemini, Kater, Crepin (Engineer-in-Chief, of Belgium), and A. Forestier
(Engineer-in-Chief of the Bridges, &c., of France).
The termite, or white ant, is the most destructive insect to timber on
land, whilst the teredo reigns supreme of sea worms in the sea. The
former we shall treat of in our next chapter, the latter we propose
considering at some length in this.
The marine worm, of which there are accounts in all parts of the world,
has been known, by its effects, for hundreds of years; indeed, Ovid spoke
of it nineteen hundred years ago, and it is even mentioned by Homer.
Fossil _terredines_ of great antiquity have been found near Southend;
also pieces of petrified wood from the greensand, near Lyme and Sidmouth,
bored by ancient species of _teredo_; also from Bath, and from Doulting,
near Shepton Mallet, specimens of oolite, with petrified corallines in
it, pierced by boring shells.
It is said that this worm is a native of India, and that it was
introduced to Holland some 200 years ago, from whence it has spread
through the ports of northern Europe.
The _Teredo navalis_[17] is very destructive to harbour works and piling.
The Southampton water is particularly infested with it; in fact, the
_teredo_ is found in every port to which coals are carried south of the
Tees; in the Thames, as high up as Gravesend; and northward as far as
Whitby. It is also found at Ryde, Brighton, and Dover. Traces of the
ravages of the _Teredo navalis_, and of the _Limnoria terebrans_, have
at various periods been found from the north of Scotland and Ireland, on
almost every coast, to the Cape of Good Hope and Van Dieman’s Land, in
the eastern hemisphere; and, in the western hemisphere, from the river
St. Lawrence to Staten Island, near Terra del Fuego, almost in the Polar
Sea; so that although this maritime scourge is rifest in warm climates,
yet cold latitudes are not exempt from it.
At the Crystal Palace, Sydenham, may be seen the destructive _Teredo
navalis_ in a bottle, and there may also be seen mahogany perforated by
it, and fir piles from Lowestoft Harbour, which were rendered useless by
the ravages of the worm and the _limnoria_ three years after they were
driven, showing the necessity of defending timber intended for marine
construction. A specimen of American oak from the dock gates of Lowestoft
Harbour, which had been four years under water, and a part of a fir-pile
from the dockyard creek at Sevastopol, also show the destructive powers
of the _teredo_. At the South Kensington and British Museums, London,
specimens of this worm may also be seen, as well as pieces of timber
perforated by it.
The bottoms of ships, and timbers exposed to the action of the sea, are
often destroyed by the _teredo_.
The gunboats constructed during the Crimean war suffered far more from
dry rot and the _teredo_ than the shot and shell of the Russians. One
cannot even guess at the mischief perpetrated every year all along our
shores, in docks and harbours, by the boring animals that penetrate all
woods not specially protected. We cannot count the number of the ships
that have foundered at sea, owing to those few inches of timber, on which
all depended, being pierced or destroyed by the worm or fungus.
In the short space of twelve years these destructive worms were known
to make such havoc in the fir piles of a bridge at Teignmouth, that the
whole bridge fell suddenly, and had to be totally reconstructed.
The wooden piers of Bridlington were nearly wholly destroyed by worms;
and the pile fenders on the stone piers at Scarborough were generally cut
through in a few years.
At Dunkirk, wooden jetties are so speedily eaten away that they require
renewal every twelve or fifteen years. At Havre, a stockade was entirely
destroyed in six months. At Lorient, wood only lasts about three years
in the sea-water; and at Aix, the hull of a stranded vessel was found
to have lost half its weight in six months, from the ravages of these
animals.
The reason why Balaclava, in Russia, is not a place of considerable
mercantile importance is owing in a great measure to the destructive
ravages of the worms with which its waters are infested, and by which the
hulls of ships remaining there for any length of time become perforated.
The piles of the jetties in Colombo Harbour, Ceylon, which are mostly
of satin-wood, and about 14 inches in diameter, are so pierced by these
worms in the course of twelve months as to require renewal.
[Illustration: _Portion of pile, from Balaclava harbour, Russia; riddled
by the Teredo Navalis._]
The cofferdam at Sheerness was destroyed by the _teredo_. After a time,
it was no uncommon occurrence to see several piles, apparently sound,
floated away at each tide; indeed, they were so thoroughly perforated by
the _teredo_ that in still weather, by putting the ear to the side of the
pile, the worms could be heard at their boring labours.
The almost total destruction of the pier-head of the old Southend Pier
in a few years, is another instance of the serious damages these worms
cause. The old pier-head was erected in the year 1833, and in three years
the majority of the wooden piles had been almost destroyed, and at the
end of ten years, in addition to the piles being all eaten through by
the worms, the whole structure had sunk 9 inches at the western end, so
that in a short time it would have fallen. The materials with which the
work was constructed were of good quality, the fir being Memel, and the
oak of English growth; it was all perfectly sound in those places were
the _teredo_ had not attacked it, and indeed portions of it were again
used in the construction of the extension of the pier. The whole of the
timber work was well coated with pitch and tar previously to being fixed,
but notwithstanding these precautions, and an apparent determination
to protect the pier-head by copper sheathing, brushing, cleaning, and
constant watchfulness, the _teredo_ made its appearance, and committed
such ravages that the entire destruction of the pier-head soon appeared
inevitable. The _Teredo navalis_ first showed itself six months after the
completion of the work, and was reported within twelve months to have
seriously injured the piles above the copper, whilst at about low-water
mark, of neap tides, nearly all the piles exhibited appearances of
destruction, the _limnoria_, as well as the _teredo_, having seriously
attacked them; and in less than four years from the completion of the
pier-head, they had progressed in their work to such an extent that
some of the piles were entirely eaten through, both above and below the
copper sheathing; in consequence of this the stability of the structure
was materially injured, and, on examination, it was discovered that
the ground had been considerably washed away by the action of the sea,
and that the piles below the copper were exposed to the action of the
_teredo_.
The first appearances of the _Teredo navalis_ are somewhat singular,
inasmuch as the wood which has been perforated by it presents to the
casual observer no symptom of destruction on the surface, nor are the
animals themselves visible, until the outer part of the wood has been
broken away, when their shelly habitations come in sight, and show the
perfect honeycomb they have formed; on a closer examination of the wood,
however, a number of minute perforations are discovered on the surface,
generally covered with a slimy matter; and on opening the wood at one of
these, and tracing it, the tail of the animal is immediately found, and
after various windings and turnings, the head is discovered, which, in
some cases, is as much as 3 feet from the point of entrance; sometimes
it will happen, especially if the wood has been much eaten, that their
shelly tubes are partly visible on the surface, but this is rare; they
enter at the surface, and bore in every direction, both with and against
the grain of the wood, growing in size as they proceed.
The Rev. W. Wood writes, in 1863: “I have now before me a portion of
the pier at Yarmouth, which is so honeycombed by this terrible creature
that it can be crushed between the hands as if it were paper, and in
many places the wood is not thicker than ordinary foolscap. This piece
was broken off by a steamer which accidentally ran against it; and
so completely is it tunnelled, that although it measures 7 inches in
length and about 11 in circumference, its weight is under 4 ounces, a
considerable portion of even that weight being due to the shelly tubes of
the destroyers.”
The eggs of the _teredo_ affix themselves to the wood they are washed
against, are then hatched, and the worm commences boring; each individual
serves by itself for the propagation of the species; and they rarely
injure each other’s habitations. Any timber, constantly under water,
but not exposed to the action of the air at the fall of the tide, is
extremely likely to be destroyed by them. They appear to enter the wood
obliquely, to take the grain of the fibre, and more generally to bore
with it downwards, where the perforations are left dry at low water.
It has been stated by some authorities that the _teredo_ is only a
destructive creature, and seeks the wood as a shelter, from instinctive
dread of some larger animals, but there is no doubt this insect feeds
upon wood. Mr. John Paton, C.E. (to whom we are indebted for much
information on these worms), in conjunction with Mr. Newport, the eminent
physiologist and anatomist, on carefully dissecting this animal for the
purpose of ascertaining its general character, and more particularly the
nature of its food, found digested portions of wood in its body, so
that there is no doubt that the _teredo_ does feed upon the particles of
the wood, and to this its rapid and extraordinary growth must be mainly
attributed.
[Illustration: _The Lyceris, which destroys the Teredo Navalis._
_The Teredo Navalis, which destroys wood._
_Portion of Timber pile destroyed by Sea Worms._]
The _Teredo navalis_, or, as it is sometimes called, the Ship Worm, is
one of the _Acephalous mollusca_, order Conchifera, and of the family
of the _Pholadariæ_. It is of an elongated vermiform shape, the large
anterior part of which constitutes the boring apparatus, and contains
the organs of digestion, and the posterior, gradually diminishing in
size, those of respiration. The body is covered with a transparent
skin, through which the motion of the intestines and other remarkable
peculiarities are plainly visible. The posterior or tail portion is
armed at its extremity, with two shells, and has projecting from it a
pair of tubular organs, through which the water enters, for the purpose
of respiration; this portion is always in the direction of the surface,
and apparently in immediate contact with the water, but does not bore.
The anterior portion of the animal is that by which it penetrates the
wood, being well armed for the purpose by having, on each side, a pair of
strong valves, formed of two pieces, perfectly distinct from one another;
the larger piece protects the sides and surface of the extremities, and
has a shelly structure projecting from the interior, to which the muscles
are attached; the smaller piece is more convex, and covers that part
which should be regarded as the anterior surface of boring. This portion
of the shell is deeply carniated, and seems to constitute the boring
apparatus. The shells form an envelop around the external tegument of
the animal, which even surrounds the foot, or part by which it adheres
to the wood. The neck is provided with powerful muscles. The manner in
which it appears to perforate the wood is by a rotary motion of the foot,
carrying round the shells, and thus making those parts act as an auger,
which is kept, or retained in connection with the wood, by the strong
adherence of the foot. The particles of wood removed by this continued
action of the foot, and the valves, are engorged by the animal, for
between the junction of the two large shells there is a longitudinal
fissure in the foot, which appears to be formed by a fold of this portion
of the two sides, thus forming a canal to the oral orifice, and along
which the particles of wood bored out, are conveyed to the mouth. The
mouth, or entrance to the digestive organs, is of a funnel shape, and
consists of a soft, or membraneous surface, capable of being enlarged,
and leading into an œsophagus, which passes backwards towards the dorsal
surface of the animal. At or near the termination of the œsophagus, there
is a glandular organ, the use of which is possibly to secrete a fluid for
assisting in the digestion of the wood, and not, as has been supposed, to
act as a solvent; for if such were the case, it would most probably be
situated at its commencement instead of at its termination. At a short
distance behind this organ are two other large glandular bodies, the
use of which may also be to secrete fluid for the purpose of digestion.
The œsophagus terminates in a large dilatation, into which these organs
pour their contents; at its posterior end the canal is dilated into a
very large elongated sac, which extends backwards to about one-fourth
of the length of the whole animal, and is filled with food, while from
its anterior, or upper surface, it has an oval, muscular formation, from
which the alimentary canal is continued forwards, and, after making a few
turns, passes backwards, in an almost direct line, on the upper surface
of the large sac, again passing backwards and forwards, until it finally
arrives at its termination, which it passes round, and then proceeds, in
a direct line, to the anal outlet. In the lower portion of the œsophagus,
and also in the sac, distinct portions of woody fibre of an extremely
minute character were found by the aid of the microscope of a power of
three hundred, and this was the character of the whole of the contents of
the alimentary canal.
The _teredo_ lines the passage in the wood with a hard shell; this shell
is formed around, but does not adhere to the body; it is secreted by the
external covering, which, in its first formation, is extremely fragile,
but becomes hardened by contact with the water, and adheres to the wood,
from which it may, however, be easily detached. The interior of this
shell is not filled by the body of the _teredo_, but a large space around
it is occupied with water, admitted through the small orifice in the
surface of the wood through which the animal first entered; the water
being drawn through the respiratory tubes, into the bronchial cavity
of the body, is expired again through the same orifice, and this, in
conjunction with the valve-like shells attached at this part, induces a
current round the animal which removes the excreted fœtal matter. The
shells are very smooth on the inner surface, but are somewhat rougher
on the exterior; they are much harder and firmer in the cells of the
older animals than in the young ones, and are composed of several annular
parts, differing greatly in their length.
It is no less curious than wonderful to observe the mysterious instinct
which apparently regulates the mechanical skill of the _teredo_, its
own body supplying it with an implement of such admirable consistency
and adaptation as to enable it to excavate a habitation for itself, so
accurately formed that to a casual observer it would appear a mystery how
so perfect a circle could be produced. It is only on examination that the
raised and hollow parts of the wood become visible, and explain, in some
degree, the auger-shaped contrivance that has been used for the purpose
of perforating.
It has already been stated, that the wood is perforated by a rotary
motion of the foot, the adhering part of which acts as a fulcrum,
carrying round the shells, and thus giving immense power to the animal in
its operations.
It is said that when Brunei was considering how to construct the Thames
Tunnel, he was one day “passing through the dockyard (at Chatham, where
he was employed by Government), when his attention was attracted to an
old piece of ship-timber which had been perforated by that well-known
destroyer of timber--the _Teredo navalis_. He examined the perforations,
and subsequently the animal. He found it armed with a pair of strong
shelly valves, which enveloped its anterior integuments; and that, with
its foot as a fulcrum, a rotatory motion was given by powerful muscles to
the valves, which, acting on the wood like an auger, penetrated gradually
but surely; and that, as the particles were removed, they were passed
through a longitudinal fissure in the foot, which formed a canal to
the mouth, and so were engorged. To imitate the action of this animal
became Brunei’s study. ‘From these ideas,’ said he, ‘by slow and certain
methods; which, when compared with the progress of works of art, will be
found to be much more expeditious in the end.’”[18]
Professor Owen suggests that the power of the _teredo_ to bore into wood
depends on muscular friction, the muscular substance being perpetually
renewed while the wood wastes away, of course, without renewal. Professor
Forbes, Dr. Carpenter, and Dr. Lyon Playfair were appointed about
twenty-five years ago by the British Association to examine into the
natural history and habits of these boring animals, but they did not
arrive at any definite conclusion as to whether the boring action of the
_teredo_ was mechanical or chemical. Dr. Deshayes, on his return from
Algiers, after making accurate drawings and careful investigations, came
to the conclusion that the borings were effected by an acid secretion.
Mr. Thomson, of Belfast, examined the operations of the _teredo_ on the
pier at Port Patrick, and arrived at the same conclusion. The general
opinion, however, is that the boring action is a mechanical one.
Although the _teredo_ appears to penetrate all kinds of timber, that
which it seems to destroy with the greatest ease is fir, in which it
works much more speedily and successfully than in any other, and perhaps
grows to the greatest size. In a fir pile, taken from the old pier-head
at Southend, a worm was found 2 feet long and ¾ inch in diameter, and
indeed they have been heard of 3 feet in length and 1 inch in diameter.
The soft, porous nature of the wood is no doubt the cause of their rapid
growth, for in oak timber they do not progress so fast, or grow to so
great a length, though in Sir Hans Sloane’s ‘History of Jamaica’ (1725)
there are accounts of these animals destroying keels of ships made of
oak, and even of cedar, although the latter is renowned, by its smell and
resin, for resisting all kinds of worms.
[Illustration: _Shell left by the Teredo Navalis._
_Cell formed by the Teredo Navalis showing method of boring._]
There is another kind of worm which is very destructive to timber,
which Smeaton observed in Bridlington piers. This is the TIMBER-BORING
SHRIMP, or GRIBBLE, the _Limnoria terebrans_ (or _Limnoria perforata_,
Leach), a mollusc of the family _Asselotes_, Leach. The _Limnoria
terebrans_ is very abundant around the British shores. Its ravages were
first particularly observed in the year 1810, by the late Sir. Robert
Stevenson, engineer of the Bell Rock Lighthouse. While engaged in the
erection of that structure he found the timber of the temporary erections
to be soon destroyed by the attacks of the _limnoria_. So little was
known of the _limnoria_ at the time that Dr. Leach, a well-known
naturalist, who received some specimens from Mr. Stevenson, in 1811,
declared it to be a new and highly interesting species. In 1834, the
late Dr. John Coldstream wrote a very full and interesting description
of the creature. The _limnoria_ resembles a woodlouse, and is so small
as hardly to be perceptible in the timber it attacks, being almost of
the same colour. Small as is this crustacean, hardly larger indeed than
a grain of rice, it is a sad pest wherever submarine timber is employed,
for it works with great energy, and its vast numbers quite compensate
for the small size of each individual; for as many as twenty thousand
will appear on the surface of a piece of a pile only 12 inches square. It
proceeds in a very methodical manner, and makes its way obliquely inward,
unless it happens to meet a knot, when it passes round the obstacle and
resumes its former direction. The surface of the timber being first
attacked, it proceeds progressively into the wood to the depth of about
1½ inch: the tunnels being cylindrical, perfectly smooth winding holes,
about ⅟16th inch in diameter: it is necessary that the holes should
be filled with salt water. The outward crust formed by these attacks
then becomes macerated and rotten, and is gradually washed away by the
beating of the sea. The _limnoria_ does not work by means of any tool or
instrument like the _teredo_, but is supposed to possess some species
of dissolvent liquor, furnished by the juices of the animal itself. Dr.
Coldstream was of opinion that the animal effects its work by the use of
its mandibles. From ligneous matter having been found in its viscera,
some have concluded that it feeds on the wood, but since other molluscs
of the same genus, _Pholas_, bore and destroy stonework, the perforation
may serve only for the animal’s dwelling. The _limnoria_ seems to prefer
tender woods but the hardest do not escape: teak and greenheart are about
the only woods it does not attack. The rate at which the _limnoria_ bores
into wood in pure salt water is said to be about one inch in a year;
but instances have occurred in which the destruction has been much more
rapid. At Lowestoft Harbour, square 14 inch piles were in three years
eaten down to 4 inches square. At Greenock, a pile 12 inches square was
eaten through in seven years. It is stated that a 3-inch oak plank, 12
feet long, would be entirely destroyed in about eight years. Joists
of timber have been found at Southend Pier, 2 feet and 3 feet below
high-water mark, where they had made rapid destruction. The _limnoria_
almost always works just under neap tides; it cannot live in fresh
water, and whilst it is destroying the surface of a pile, the _teredo_
is attacking the interior: sometimes the former is found attacking the
same timber as the Chelura. As with most of these creatures, the male
_limnoria_ is smaller than the female, being about one-third her size.
The female may be distinguished by the pouch in which the eggs and
afterwards the young are carried. About six or seven young are generally
found in the pouch.
The WOOD-BORING SHRIMP (_Chelura terebrans_) is a crustacean that nearly
rivals the _teredo_ itself in its destructive powers. It makes burrows
into the wood, wherein it can conceal itself, and at the same time
feast upon the fragments, as is proved by the presence of woody dust
within its interior. Its tunnels are made in an oblique direction, not
very deeply sunk below the surface, so that after a while the action of
the waves washes away the thin shell, and leaves a number of grooves
on the surface. Below these, again, the creature bores a fresh set of
tunnels, which in their turn are washed away, so that the timber is soon
destroyed in successive grooved flakes.
According to Mr. Allman, its habits can be very easily watched, as if
it is merely placed in a tumbler of sea water, together with a piece of
wood, it will forthwith proceed to work, and gnaw its way into the wood.
The apparatus with which it works this destruction is a kind of file or
rasp, which reduces the wood into minute fragments. In this creature
the jaw feet are furnished with imperfect claws, and the tenth segment
from the head is curiously prolonged into a large and long spine. The
great flattened appendages near the tail seem to be merely used for the
purpose of cleaning its burrow of wood dust which is not required for
food. The creature always swims on its back, and when commencing its work
of destruction, clings to the wood with the legs that proceed from the
thorax. The wood-boring shrimp is one of the jumpers, and, like the sand
hopper, can leap to a considerable height when placed on dry land. It
has been detected in timber taken from the sea at Trieste. It was first
observed as an inhabitant of the British seas several years ago, by Mr.
Robert Ball, of Dublin, and in January, 1847, it was described by Mr.
Mullins, C.E., in a paper read before the Institution of Civil Engineers
of Ireland, as being very injurious to the timber piles in Kingstown
Harbour, near Dublin, and far more destructive than the _Limnoria
terebrans_.
[Illustration: LIMNORIA TEREBRANS. FEMALE. MALE.
A. B. C. HEAD OF THE TEREDO NAVALIS.
RASP OR FILE OF THE CHELURA. CHELURA TEREBRANS.
ELEVATION OF PILES, SOUTHEND PIER, DESTROYED BY THE “TEREDO” AND
“LIMNORIA” ABOVE AND BELOW THE COPPER SHEATING.]
We have already referred to the _lesson_ the celebrated engineer,
Brunel, received from observing the _teredo_; and we can state that
architects have also received _lessons_ from nature. Sir Christopher
Wren constructed his spire of St. Bride’s Church, London, after observing
the construction of the delicate shell, called _Turretella_, which has
a central column, or newel, round which the spiral turns. Brunelleschi
designed the dome of Sta. Maria, at Florence, after studying the bones
of birds and the human form; and Michael Angelo followed Brunelleschi in
constructing the dome of St. Peter’s, Rome.[19]
The LEPISMA is also a destructive little animal, which begins to prey
on wood in the East Indies, as soon as it is immersed in sea water. The
unprotected bottom of a boat has been known to be eaten through by it in
three or four weeks.
These worms, it must be remembered, do not live except where they have
the action of the water almost every tide, nor do they live in the parts
covered with sand. The wooden piles of embankments and sea locks suffer
very much from their depredations, and in the sea dykes of Holland they
cause very expensive annual repairs.
The Dutch used to coat their piles with a mixture of pitch and tar, and
then strew small pieces of cockle and other shells, beaten almost to
powder, and mixed with sea sand, which incrusted and armed the piles
against the attacks of the _teredo_. We believe it was a frequent
practice in London, about half a century ago, to place small shells in
the wooden pugging between the floor joists to deaden sound.
Having described the chief peculiarities of these worms, shown their
mode of working, and the extent to which their destructive powers may be
carried, it will now be necessary to consider the various schemes which
have been proposed and tried to prevent their desolating ravages. These
may be divided into _three_ classes, viz. the natural, chemical, and
mechanical.
1st. By using woods which are able to resist the attacks of sea worms.
2nd. By subjecting piles to a chemical process.
3rd. By adopting a mechanical process.
First. We have not any English woods which resist their attacks. Elm
(used for piles in England) or beech (used for piles, if entirely under
water, in France) cannot withstand the _teredo_; while oak cannot battle
successfully against wood-beetles in carvings. It is therefore necessary
to inquire whether foreign woods are any better.[20] Unfortunately the
great expense of importing them into England prevents their use for piles.
Nearly all our foreign woods used for engineering and building purposes
come from the Baltic or Canada: they are fir and pine. Memel timber from
the Baltic is comparatively useless unless thoroughly creosoted; and
Canadian timber is not so good as the Baltic wood. At Liverpool and some
of the western ports of England Canadian timber is preferred to Baltic,
although we believe the reason to be that they cannot get the latter,
except in small quantities at a time.
The following is a list of timber woods which, according to good
authorities, resist for a long period of time the attacks of sea worms.
It should be borne in mind, however, that the timber should be cut,
during the proper season, from a large and full-grown tree; and, to
prevent splitting, it should be kept from the direct action of the sun
when first cut; it should have all the bark and sapwood removed, and
allowed to dry a certain time before being used.
WOODS WHICH RESIST SEA WORMS.
_Australia, Western._--Jarrah, beef-wood, tuart.
_Bahama._--Stopper-wood.
_Brazil._--Sicupira, greenheart.
_British Guiana._--Cabacalli, greenheart, kakarilly, silverballi
(yellow).
_Ceylon._--Halmalille, palmyra, theet-kha, neem.
_Demerara._--Bullet, greenheart (purple heart-wood), sabicu.
_India._--Malabar teak, sissoo, morung sál, dabu, than-kya,
ilupé, anan, angeli, may-tobek. (Teak resists the _teredo_, but
is not proof against barnacles.)
_Jamaica._--Greenheart.
_North America._--Locust.
_Sierra Leone._--African oak, or tortosa.
_South America._--Santa Maria wood.
_Philippine Islands._--Malacintud, barnabá, palma-brava.
_Tasmania._--Blue gum.
_West Indies._--Lignum vitæ.
Second. The chemical, viz. Kyan’s process of corrosive sublimate; Payne’s
process of sulphate of iron and muriate of lime; pitching and tarring;
Burnett’s process of chloride of zinc; and arsenic, or other mercurial
preparations, have all failed, with the exception of Bethell’s process of
oil of tar. The failure must proceed from one of two causes; either that
the sea-water decomposes the poisonous ingredients contained in the wood,
or that these poisonous compounds have no injurious effect on the worms;
it appears, however, that both these causes have been in operation,
principally the latter.
Without a series of the most minute experiments, it is impossible to
form any general notion of the action of sea-water on timber. Common
salt, chlorides of calcium and magnesium, sulphate of soda, iodides
and bromides of the same metals, are known to exist in sea-water, and
in great abundance in the torrid zone. What effect these different
ingredients may have upon saturated timber it is difficult to say, but it
is extremely probable that they do have an effect.
With regard to the different poisonous compounds having no injurious
effect on the worms, it should be remembered that all cold-blooded
animals are much more tenacious of life than those of a higher
temperament, and in descending the scale of animal creation, the tenacity
of life increases, and this principle is more developed. A frog, which
though cold-blooded, is an animal of a much higher order than the
_teredo_, will not only live in hydrogen gas, but also in a strong
solution of hydrocyanic acid, while at the same time a single drop placed
on the nose of a rat, or in the eye of a rabbit, would produce instant
death. A somewhat similar occurrence is noticed in the ‘British and
Foreign Medical Review,’ for July, 1841, showing the slow effects of
prussic acid on the common snake and turtle.
It may therefore be inferred, that as it requires a large quantity of the
most virulently poisoned matter to destroy animals of a much higher order
than the _teredo_, it would take a still greater quantity to affect those
animals as they exist in their own element.
The preserving property of soluble salts, such as corrosive sublimate,
sulphate of copper, &c., was considered to be founded upon their power
of coagulating the albumen, and the sap of wood, thereby rendering that
sap less liable to decay; but that very quality of combining with the
albumen, destroyed the activity of the poison of the salts. A given
quantity of corrosive sublimate of mercury, which if administered to a
dog would kill it, would, when mixed with the white of an egg, become
coagulated, and if swallowed in that state would be perfectly harmless;
so a piece of wood, saturated by those salts, could be eaten by a worm
without injury.
A French naturalist, M. de Quatrefages,[21] in 1848, suggested that a
weak solution of mercury (corrosive sublimate) thrown into the water will
destroy the milt of the _teredo_, and consequently prevent fecundation
of the eggs, thus exhausting the molluscs in the bud. He proposed that
ships should be cleared of this terrible pest by being taken into a
closed dock, into which a few handfuls of corrosive sublimate should
be thrown and well mixed with the water. He considered that about 1
lb. of sublimate would be sufficient for 20,000 cubic metres (metre =
39·37 English inches) of water; but on account of the cost it would
be advisable to use salts of lead or copper. This proposition of de
Quatrefages reminds us of Chapman’s suggestion, in 1812, to get rid of
dry rot in ships, viz. by sweeping out the hold, laying from two to four
tons of copperas in her bottom, and as much fresh water let in upon it as
would make a saturated solution to soak into the wood.
M. de Quatrefages placed the four salts he used in his experiments in
the following order, according to merit: 1st, corrosive sublimate; 2nd,
acetate of lead; 3rd, sulphate of copper; and 4th, nitrate of copper.
In America, white oxide of zinc is used as a marine paint for ships
and piles. In the United States Navy Yard at Gosport it is spoken well
of, and very frequently employed. It is said to be much superior to
white-lead, red-lead, verdigris, or coal-tar, and that timber covered
with two coats of white zinc is neither attacked by the worm, nor do
barnacles attach to it when immersed in salt water.
We can only find one instance of timber impregnated with water-glass
having been tested against this subtle foe. Water-glass is certainly
worth a further trial.
The instance we refer to occurred about forty years ago. In 1832,
Dr. Lewis Feuchtwanger, of New York, was permitted by the Ordnance
Department, under the direction of Commodore Perry, to perform
experiments with water-glass on piles in the Brooklyn Navy Yard, and in
various docks. The piles in the docks were destroyed by the _teredo_ so
fast that they _had to be replaced every three years_. The experiments
proved highly satisfactory: the piles which had been so treated lasting
many years, without any indication of being attacked by sea-worms.
The reader is referred to some works on water-glass mentioned below,[22]
which are worthy of attentive perusal.
Third. The mechanical processes. They are few in number, and rather
expensive.
At Saint Sebastian, in Spain, the piles of the wooden bridge standing
in the sea have been guarded against the attacks of sea-worms in the
following manner: Each pile is surrounded by a wooden box, and the space
between filled up with cement. After six years it was proved that the
piles were in a perfect condition, whilst the outer boxes were completely
riddled by the worms. A similar method to this was adopted, some years
since, to many of the piles in the Herne Bay Pier, which were affected
by sea-worms. Several attempts had been made to protect the timber, by
saturating it under various processes, with, however, only doubtful
success. At last, a wooden casing was formed round each pile, leaving
a space of about an inch all round, which was rammed full of lime or
cement concrete. That process appeared to be perfectly successful, as the
pier-master, who first adopted the method, stated that some of the piles
had been so treated for three or four years, and although the worms had
commenced their ravages, they appeared to have been checked, and not to
have been able to exist when so enclosed.
In 1835, Brunel suggested an easy way of defending piles, which was to
give them in the first instance a coat of tar; then powder them with
brick-dust, which would render the wood sufficiently hard to receive a
coat or two of cement. This is similar to the Dutch method.
Some foreigners use sheet lead nailed on to piles, and wrapped close
round with well-tarred rope.
Copper sheathing has often been used for the protection of piling in
piers and harbours. The destruction of copper by the action of sea-water
is a matter which has long occupied the attention of scientific men, and
it appears to be well ascertained that the decay does not result from the
bad quality of the copper, for, according to Mr. Wilkinson, no difference
could be discovered between the composition of copper that had endured
well, and that which had been rapidly destroyed. Copper sheathing was
used at Southend, but without success, for although nearly all the piles
were covered with it for about 9 feet or 10 feet, the _limnoria_ not only
penetrated between the copper and the timber, but the copper had decayed
to such an extent as in some cases to be no thicker than the thinnest
paper; it was soft, and peeled off the wood very easily, and in two or
three years would probably have been entirely destroyed.
Covering the surface of the timber with broad-headed scupper nails,
arranged in regular rows with their heads at no great distance from each
other, is a method which has been satisfactorily employed in various
parts of the world, in Swedish and Danish vessels, even up to the
present time, and, indeed, it was also practised by the Romans. The
scupper-nailed piles at Southend, after twelve years’ exposure to the
sea, were perfectly sound, and although the nails were not driven close
together in the first instance, yet the corrosive action was so great as
to form a solid impenetrable metallic substance, upon which the worms
refused to settle. Scupper nails have been proved at Yarmouth, as well
as at other places, to have protected timber for forty years, but the
process is expensive, as it costs one shilling per square foot. They
should be about half an inch square at the head.
Captain Sir Samuel Brown, R.N., states that from numerous experiments and
observations, he is satisfied that at present there is really no specific
remedy against the attacks of sea-worms upon timber, except iron nails.
He proposes to encase the piles with broad-headed iron nails resembling
scupper nails, but considerably larger, and he says that in the course of
a few months corrosion takes place, and spreads into the interstices. The
rust hardens upon the pile, and becomes a solid mass which the worm will
not touch. Experiments tried at the Trinity Pier, Newhaven, and Brighton
Pier, have established the effectiveness of his method.
At the Cape of Good Hope, and many other places, wood piles are cased
in iron, and occasionally iron piles are used instead of wood, at great
cost. Further experience is desirable as to the durability of cast
iron[23] in salt water, especially as to its peculiar property of
conversion, after a few years’ immersion in the sea, into a carburet of
iron, closely resembling plumbago, so that it may be easily cut with
a knife. This, of course, diminishes its powers of resistance acting
upon the framing it is intended to strengthen. In the course of the
construction of the Britannia Bridge, about one hundred thin plates
were delivered, which were not used on account of some error in their
dimensions. They were left on the platform alongside the straits,
exposed to the wash and spray of the sea; and after about two years were
literally so completely decomposed as to be swept away with a broom into
the water, not a particle of iron remaining.
We have already stated that the chemical processes have failed with the
exception of Bethell’s process of oil of tar, generally known as the
creosoting process. This method, _when properly carried out_, thoroughly
protects wood from the ravages of the _teredo_ and other marine worms.
The breakwaters and piers at Leith, Holyhead, Portland, Lowestoft, Great
Grimsby, Plymouth, Wisbeach, Southampton, &c., have been built with
creosoted timber, and in no case have the _Teredo navalis_, _Limnoria
terebrans_, or any other marine worms or insects been found to attack
these works, as certified to by the engineers in whose charge the several
works are placed. In the cases of Lowestoft and Southampton we are
enabled to give the detailed reports.
A most searching examination, lasting many days, was made in 1849, upon
every pile in Lowestoft Harbour, by direction of Mr. Bidder; and the
report of Mr. Makinson, the Superintendent of Lowestoft Harbour Works,
contains the subjoined statement:
“The following is the result, after a close and minute investigation of
all the piles in the North and South Piers.
“_North Pier._--The whole of the creosoted piles in the North Pier, both
seaward and inside the harbour, nine hundred in number, are sound, and
quite free from _teredo_ and _limnoria_.
“_South Pier._--The whole of the creosoted piles in the South Pier, both
seaward and inside the harbour, seven hundred in number, are sound, and
quite free from _teredo_ and _limnoria_.
“There is no instance whatever of an uncreosoted pile being sound. They
are all attacked, both by the _limnoria_ and the _teredo_, to a very
great extent, and the piles in some instances are eaten through. All the
creosoted piles are quite sound, being neither touched by the _teredo_ or
the _limnoria_, though covered with vegetation, which generally attracts
the _teredo_.”
There was only one instance of a piece of creosoted wood, in Lowestoft
Harbour, being touched by a worm, and that was occasioned by the workmen
having cut away a great part of one of the cross heads, leaving exposed
the interior or heart of the wood, to which the creosote had not
penetrated. At this spot a worm entered, and bored to the right, where
it found creosote; on turning back and boring to the left, but finding
creosote all around, its progress was stopped, and it then appeared to
have left the piece of wood altogether.
In 1849, Mr. Doswell, who had the conduct of experiments on different
descriptions of wood at Southampton, where the river was so full of the
worm that piles of 14 inches square had been eaten down to 4 inches in
four years, reported as follows: “From my examination, last spring tides,
of the specimen blocks attached, on the 22nd February, 1848, to some
worm-eaten piles of the Royal Pier, I am enabled to report that Bethell’s
creosoted timbers all continue to be unaffected by the worms; that the
pieces saturated with Payne’s solution continue to lose in substance by
their ravages; and that the unprepared timbers diminish very fast, except
the American elm, which stands as well (or nearly so) as that prepared by
‘Payne’s solution.’”
The following are the detailed particulars:
BETHELL’S CREOSOTED BLOCKS, PLACED FEBRUARY 22, 1848.
Memel, at low water of spring tides } Unaffected by worms.
Red pine, at low water of neap tides }
Yellow fir, at high water of neap tides A few barnacles.
PAYNIZED BLOCKS, PLACED APRIL 6, 1848.
Red pine, at low water of spring tides Worm-eaten.
American elm, at low water of neap tides } A few barnacles.
Fir, at high water of neap tides }
UNPREPARED BLOCKS, PLACED APRIL 6, 1848.
Memel, at low water of spring tides Much worm-eaten.
American elm, at low water of neap tides A few barnacles.
Fir, at high water of neap tides Much worm-eaten.
On 1st January, 1852, Mr. Doswell ascertained that, notwithstanding the
number of _teredines_ and _limnoria_ to be found in the Southampton
Waters, none of the creosoted blocks had been attacked by them.
According to M. Forestier, similar results have been obtained at
Brighton, Sunderland, and Teignmouth.
Allusion has already been made to Mr. Pritchard, of Shoreham, with
reference to preserving timber. On July 26, 1842, he presented a report
to the Treasurer of the Brighton Suspension Chain Pier Company, upon the
preservation of timber from the action of sea-worms. We give a portion of
it, as follows:
“Stockholm tar has been used, and proved to be of little service; this
tar is objectionable owing to its high price, and also from its being
manufactured from vegetable substances. All tars containing vegetable
productions must be detrimental to the preservation of timber, especially
when used in, and exposed to, salt water. This tar does not penetrate
into the wood, and in a very few months the salt acid of the sea will eat
it all away.
“Common gas or coal tar has been used to a great extent, and its effects
are apparent to all. It does a very great deal of harm, forms a hard or
brittle crust or coat on the wood, and completely excludes the damp and
unnatural heat from the possibility of escape, owing to its containing
ammonia, which burns the timber, and in a few years it turns brown
and crumbles into dust. Indeed, timber prepared with this tar will be
completely destroyed on this coast and pier by the ravages of the _Teredo
navalis_, and the _Limnoria terebrans_, in five or six years.
“Also Kyan’s patent, or the bi-chloride of mercury, has been used, but
has proved equally useless. The sleepers Kyanized five years ago, and
in use at the West India Dock warehouses, have been discovered to decay
rapidly, and the wooden tanks at the Anti-Dry-Rot Company’s principal
yard are destroyed.
“I would recommend you for the future to use ‘oil of tar and pyrolignite
of iron’ (Bethell’s patent). This process will, without a doubt, succeed.
I have proved in hydraulic works on this coast that it will fully prevent
the decay in timber piles, destroy sea-worms, and supersede the necessity
of coating the piles with iron nails. In Shoreham Harbour, for instance,
there is a piece of red pine accidentally infused with pyrolignite of
iron, which after being in use twelve years is perfectly sound. There is
another waleing piece, the very heart of English oak, Kyanized, and in
use only four years, which is like a honeycomb or network, completely
eaten away by the _teredo_ and other sea-worms. I have fully proved the
efficiency of this method at different harbours and docks. Sixteen years
ago I had timber prepared with it, and in use on the shores of the Dee,
and it is at the present moment perfectly sound. The pyrolignite of iron
must be used of very pure quality; the timber must be dry; afterwards
the oil of tar must be applied, and not on any account must it contain a
particle of ammonia. The immense destruction on the coast of timber by
the sea-worms, and the important fact that at the Chain Pier there are
not twenty of the original piles remaining at the present time, is of
itself sufficient to awaken anxiety.”
With regard to the opinion of foreigners on the subject of creosoting,
we cannot do better than quote the report of the commission or committee
(instituted in 1859) of the Royal Academy of Sciences, Holland, upon the
means of preserving wood from the _teredo_, published at Haarlem in
1866. It is as follows:
“To conclude, it results from experiments which the committee has
directed during six consecutive years, that--
“1st. Coatings of any sort whatever applied to the surface of the timber
in order to cover it with an envelop upon which the young _teredo_ will
not fasten offer a very insufficient protection; such an envelop soon
becomes damaged, either by mechanical action, such as the friction of
water or ice, or by the dissolving action of water; and as soon as any
point upon the surface of the wood is uncovered, however small it be, the
_teredoes_ of microscopic size penetrate into the interior of the wood.
“Covering wood with plates of copper, or zinc, or flatheaded nails are
expensive processes, and only defend the wood as long as they present a
perfect and unbroken surface.
“2nd. Impregnation with soluble metallic salts generally considered
poisonous to animals does not preserve the wood from the invasions of
the _teredo_; the failure of these salts is partly attributable to their
being soaked out of the wood by the dissolving action of the sea-water,
partly also to the fact that some of these salts do not appear to be
poisonous to the _teredo_.
“3rd. Although we cannot venture to say that there may not be found in
the colonies a wood that may resist the _teredo_, yet we may affirm that
hardness of any timber is not an obstacle to the perforations of this
mollusc. This has been proved by the ravages it has made on the Gaïac and
Mamberklak woods.
“4th. The only means which can be confidently regarded as a preservative
against the ravages of the _teredo_ is the creosote oil; nevertheless,
in the employment of this agent great care should be taken regarding the
quality of the oil, the degree of penetration, and the quality of the
wood treated.”
These results of the experiments of the committee are confirmed by the
experience of a large number of engineers of ponts et chaussées (bridges
and causeways) in Holland, England, France, and Belgium. For example,
very lately a Belgian engineer, M. Crepin, expressed himself as follows
in his Report, dated 5th February, 1864, upon experiments made at Ostend:
“The experiment now appears to us decisive, and we think we may conclude
that fir timber well prepared with creosote oil of good quality is proof
against the _teredo_, and certain to last for a long time. Everything
depends, therefore, upon a good preparation with good creosote oil, and
on the use of wood capable of injection. It appears that resinous wood is
easiest to impregnate, and that white fir should be rejected.”
M. Forestier, the able French engineer at Napoléon-Vendée sums up as
follows the results of the experiments undertaken by him in the port of
Sables-d’Olonne, viz.:
“These results fully confirm those obtained at Ostend, and it appears
to us difficult not to admit that the experiments of Ostend and Sables
d’Olonne are decisive, and prove in an incontestable manner that the
_teredo_ cannot attack wood properly creosoted.”
It thus appears that there are three preservative methods, which,
according to experience, will save timber piles from the ravages of the
worms, viz.: 1st. By using woods able to resist unaided their attacks.
2nd. The mechanical method, which is, by covering the piles with scupper
nails, &c. This process is, however, very expensive, especially as the
four sides of the pile must be covered; and, moreover, it affords no
protection to the timber from internal rot or decay. 3rd. The chemical,
or “creosoting” method. This process is cheaper than the last; it
preserves the wood from decay, and no worms will touch it.
When unprepared piles are placed in the sea, there is every probability,
sooner or later, of their being attacked by the _teredo_. This animal,
however, is not left in peaceable enjoyment of the dwelling which it has
constructed, and the food which it loves, but is liable to be attacked
by an enemy, an _annelide_, to which the late M. de Haan has given
the name of _Lycoris fucata_. This animal is to be found wherever the
_teredo_ exists, indeed its eggs and larva are to be met with in the
midst of those of the mollusc. M. Kater has remarked that the adult
_lycoris_ dwelling in the mud which it enters during winter, and into
which the piles are driven, climbs up the pile to the hole formed by the
_teredo_, where, in some manner, it sucks or eats its victim; then having
enlarged the entrance to the hole, it enters and rests in the place of
the _teredo_. After a time it goes back to the entrance, and commences to
seek for fresh prey.
The _lycoris_ is narrow and not very long, provided laterally with a
great many little feet terminating in points and covered with hair, and
having in front a pair of hard superior jaws, pointed horns, and the
inferior jaws bent round in the form of hooks. Behind the head are four
pairs of tubuliform gills. It is with these arms that this little animal
pursues and devours the _teredo_.
One day M. Kater was fortunately able to observe the operations of the
_lycoris_, One of these animals coming out of a hole in the wood which
he inhabited, seized upon a _teredo_, which M. Kater had previously
deposited at the bottom of the vessel containing the wood. He saw the
_annelide_ seize the _teredo_, hurry away with it to the hole which he
occupied, and so completely devour it that he finally left only the two
valves of the shell. Our illustrations of the _teredo_ and _lycoris_
are derived from the works of Mr. Paton and M. Forestier; and our own
sketches.
If the _lycoris_ would only destroy the _teredo_, when the mollusc was in
its infancy, what an invaluable little annelide it would be!
It appears to us a great pity that the woods we have named, or some of
them, are not brought over to England in large quantities for harbour
works. In Ceylon and India, the trees are felled by Indian wood-cutters
at little cost; they are then dragged to the river banks by elephants
or buffaloes, to be floated down the rivers to the different ports, so
that labour is cheap. The question then remains, how to get the woods
to England? When the ‘Great Eastern ship has finished carrying cables,
perhaps its owners will not object to send the ship on a few voyages
with heavy cargoes to India, Demerara, &c., bringing home “teredo-proof
woods,” _at moderate charges for freight_?
Finally, to place the subject in a practical form, we think the
Institute of Civil Engineers, of London, would be heartily thanked by
the engineering world if they would appoint a committee to inquire into
the damages done to works by sea-worms; why they are found in some parts
of a roadstead or harbour, and not in others; to consider the different
remedies which have been proposed, their cost, and method of application;
what course should be adopted to prevent sea-water injuriously affecting
iron piles; and lastly, to publish a detailed account of their
experiments and recommendations.