THE FLOUR-MOTH (_Ephestia kühniella_) IN SOLDIERS’
BISCUITS
Where moth ... doth corrupt. (MATT. vi. 19.)
IT is not only those insects that destroy the continuity of our
soldiers’ integument which play a part in war. It has been well said
that an army marches on its stomach; and the admirable commissariat
arrangements which have been so distinctive a feature of the British
Expeditionary Force during the present war are the result of much
patient care and attention during times of peace. I am in no position
to discriminate, but I do believe that the admirable service of the
A.S.C. and the R.A.M.C. is at least equal to the splendid record of
those in the fighting-line.
Every one knows that recruits are frequently rejected for some defect
in their teeth. A soldier, indeed, requires strong teeth, for his
farinaceous food in the field is largely supplied to him in the form of
biscuits—not that ‘moist and jovial sort of viand,’ as Charles Dickens
described the Captain biscuit, but ‘hard-tack’ which challenges the
stoutest molars.
During the summer of 1913 the authorities of the British Museum at
South Kensington arranged a very interesting but somewhat gruesome
exhibit in their Central Hall. The exhibit consisted mainly of Army
biscuits eaten through and through by the larva of a small moth and
covered by horrible webs or unwholesome-looking skeins of silky threads.
[Illustration: FIG. 10.—_Ephestia kühniella._ Moth-infested biscuit.]
Together with these derelict biscuits were certain long metallic
coils and other apparatus used in investigating certain phases of
the life-history of the moth and the manufacture of the biscuit. The
exhibit illustrates an article which had recently appeared on the
Baking of Army Biscuits, by Mr. Durrant and Lieut.-Colonel Beveridge,
on the ‘biscuit-moth’ (_Ephestia kühniella_), a member of the family
Pyralidae. The article recorded their efforts to arrive at a means of
checking this very serious pest to service stores.[6]
The biscuit-moth (_E. kühniella_) was described two years before
its larva had been noted damaging flour at Halle. There has always
been a certain amount of international courtesy in attributing
the _provenance_ of insect pests to other countries; and when _E.
kühniella_ began, about ten years later, to attract attention in
England it was believed to have been introduced from the United States,
via the Mediterranean ports, in American meal. The American origin was,
however, denied by Professor Riley, who, in a letter to Miss Ormerod,
states, ‘I think I can safely say that this species does not occur in
the United States.’ At the moment of writing these words Professor
Riley was in the act of packing-up to leave Washington for Paris.
Possibly he was excited, certainly he was inaccurate, for the species
was then known to be prevalent in Alabama, North Carolina, and other
States. In fact, to-day it is recorded throughout Central America and
the Southern States, and in most of the temperate regions of the New
World.
[Illustration: FIG. 11.—_Ephestia kühniella._ × 2.]
The moth itself is a rather insignificant, small insect, of a
slatey-grey colour. Its eggs, rather irregular ovoids, are laid upon
the biscuit into which the issuing larvae bore. These latter are soft
and like most creatures which live in the dark, whitish, though with a
tinge of pink; the head, however, is brown and hardened. The larva is
constantly spinning silken webs or tissues, which in the most untidy
way envelop the biscuit. It finally entombs itself in a whitish silken
cocoon, and herein it ultimately turns into a chrysalis or pupa.
Another Pyralid moth—_Corcyra cephalonica_—makes similar unpleasant
webs all over biscuits, rice, or almost any farinaceous food; but,
since its larvae are unable to live unless there be a certain degree
of moisture in its food, it is less injurious to baked food than the
_Ephestia_, for whose larvae nothing can be too dry. _Corcyra_ seems
originally to be a pest of rice, and to have been introduced into
Europe with Rangoon rice; but it readily alters its diet in new
surroundings, and will live on almost any starchy stuff, if not too
desiccated.
The problem that Lieut.-Colonel Beveridge and Mr. Durrant, of the
British Museum, set out to solve was at what stage in the manufacture
of the Army biscuits does our soldiers’ food become infested, and
whether any steps could be taken to avoid or minimise such infestation.
[Illustration: FIG. 12.—_Ephestia kühniella._ A, Larva; B, pupa.
Greatly magnified.]
First, as to infestation. The biscuit must become infested either (1)
at home before packing, (2) during transit, or (3) in the country where
they are stored. The biscuits are packed in tins, hermetically sealed,
and enclosed in wooden cases to prevent injury; it was therefore
obvious that if insects could be found within intact tins it would
be demonstrated at once that infestment must have taken place in the
factories, and not subsequently.
[Illustration: FIG. 13.—_Corcyra cephalonica._ Moth-infested biscuit.]
With a view to determine the origin of infestation sample tins were
withdrawn from stocks at various stations abroad, and inspected by
experts at Woolwich; and tins which, after careful examination, had
been pronounced intact, were found to contain _Ephestia kühniella_ and
_Corcyra cephalonica_ in various stages of development, thus proving
conclusively that infestation had taken place in the factories before
the tins were soldered, and indicating that preventive or remedial
measures must be undertaken within the biscuit-making factories
themselves.
It is obvious either that the heat to which the biscuit is subjected
in the process of baking is insufficient to destroy any of the insect
eggs present in the moist dough or that the moths and beetles deposit
their eggs in or on the biscuits after baking, and during the process
of cooling and of packing into the tins. Cooling before packing is
necessary in order to allow the moisture in the centre of the biscuit
to become evenly distributed throughout the ‘tissue’ of the biscuit.
And it is during the time occupied in cooling and packing that the
biscuit is exposed to the greatest risk of infestation; any risk
occasioned by subsequent injury must be exceptional, and is probably
negligible.
By a series of most ingenious experiments, the two investigators were
able to determine the temperature in the centre of the biscuits during
the various stages of its baking and cooling. Army biscuits are made
from dough which contains about 25 per cent. of water. When stamped
out they are placed in rows on the revolving floor of an oven, and
are submitted to a high temperature for twenty minutes whilst they
travel over a space of 40 feet. The dough at first contains, as we have
said above, 25 per cent. of water, but during baking this is reduced
to about 10 per cent., and the moisture now collects in the centre of
the mass of the biscuit in consequence of the external hardening or
‘caramelisation,’ as it is called. The holes which are pricked in so
many biscuits of course help to equalise the spread of the moisture
throughout the biscuit.
Too little attention has been paid to the internal temperature of
edibles which are being cooked. Very few people, for instance, have any
conception of what is going on in the centre of a joint of meat whilst
it is being roasted or boiled. After two hours’ boiling the temperature
in the centre of a large ham has only risen to 35° C.; after six hours’
boiling to 65° C., and it is only after ten hours’ continuous boiling
that 85° C. is reached. I have, I am sorry to say, no conception as to
how long a ham ought to be boiled, but it is obvious that to be really
effective against such parasites as _Trichinella_—the _causa causans_
of trichinosis—the cooking of pork and ham should be more prolonged and
thorough than seems to be customary. But that is another story.
However, to return to our biscuits. The Colonel and Mr. Durrant
devised an ingenious instrument which determined the rising temperature
at the centre of our Army biscuits whilst baking. When the tip of
their recording apparatus lay within the moist area of the biscuit,
the temperature registered was only a little over 100° C.; but when
the tip of the instrument rested on the hard ‘caramelised’ portion
much higher temperatures were observed—even as high as 125° C. Colonel
Beveridge and Mr. Durrant were thus able to establish the fact that
the temperatures of the biscuit were, during baking, such as to rule
out the idea that the eggs of the biscuit-moth—which do not survive a
temperature of 69° C. for twelve minutes—were deposited in the biscuit
before cooking.
After the baking is completed the biscuits are cooled, and it is
at this period that they are most exposed to risk of infestation
by _Ephestia kühniella_. This insect is a well-known nuisance in
Flour-mills. So persistent and numerous are these moths at times that
they clog the rollers with their cocoons, and sometimes completely
stop them. The webbing of the elevators in the mills gets covered with
them and with their silky skeins, and then the elevators stop working.
They mat together the flour and meal with their silken excreta, and so
uniform is the temperature of the Mill, and so favourable to the life
of the insect, that they complete their life-cycle in this country in
two months, and in the warmer parts of America even more rapidly. In
well-heated mills the proceeding is continuous, so that six generations
at least may be produced each year.
The most efficient method of getting rid of this pest of the Army
biscuit is a complete and thorough fumigation of the infested premises
with carbon bisulphide. But, as this substance is not only poisonous
but inflammable, it is well to get a chemist to undertake the
proceeding, and also to notify the Insurance Company. Fumigation by
sulphur ruins the flour. Another remedial measure is that of turning
the steam from the boilers on to all the infected machinery and walls.
That this destruction of the Army biscuit is a matter of considerable
importance is shown by the fact that biscuit-rations exported to the
colonies in hermetically sealed tins have become quite unfit for
consumption, and this destruction has been noted in places as far
distant from each other as Gibraltar, the Sudan, Mauritius, Ceylon,
South Africa, and Malta. That it is also an old trouble is shown by the
following quotation from the diary which Sergeant Daniel Nicol, of the
92nd (the Gordon Highlanders), kept during the expedition to Egypt in
1801:—
Some vessels were dispatched to Macri Bay for bullocks, and others
to Smyrna and Aleppo for bread which was furnished us by the Turks—a
kind of hard dry husk. We were glad to get this, as we were then put
on full rations, and our biscuits were bad and full of worms; many of
our men could only eat them in the dark.[7]
With regard to the actual baking of the biscuit, Colonel Beveridge and
Mr. Durrant suggest that the temperature conditions during the process
of cooling should be made as unfavourable as possible for the moths by
introducing screened cool air, which can be forced in at one end of the
cooling-chamber and sucked out at the other. Could such a scheme be
adopted it would be difficult, if not impossible, for the moths to lay
their eggs, and the biscuit would thus be more rapidly cooled. In any
case it should not be difficult to ensure that the cooling takes place
in some chambers which are practically free from these destructive
moths.