THE ARBUTUS CATERPILLAR
I have not found many species of urticating caterpillars in the small
corner of my investigations. I know of two only: the Pine Caterpillar
and the Arbutus Caterpillar. The latter belongs to the genus Liparis.
His Moth, who is a glorious snowy white, with the last rings of the
abdomen bright russet, is very like Liparis auriflua, Fab., from whom
she differs not only in size—she is smaller—but, above all, in the
field of operations selected by her caterpillar. Is the species
classified in our lists? I do not know; and really it is hardly worth
while to enquire. What does a Latin name matter, when one cannot
mistake the insect? I shall be sparing of detail concerning the Arbutus
Caterpillar, for he is far less interesting in his habits than the Pine
Processionary. Only his ravages and his poison deserve serious
attention.
On the Sérignan hills, sunny heights upon which the Mediterranean
vegetation comes to an end, the arbutus, or strawberry-tree, abounds: a
magnificent shrub, with lustrous evergreen foliage, vermilion fruit,
round and fleshy as strawberries, and hanging clusters of little white
bells resembling those of the lily of the valley. When the frosts come
at the approach of December, nothing could be more charming than the
arbutus, decking its gay verdure with both fruits and flowers, with
coral balls and plump little bells. Alone of our flora, it combines the
flowering of to-day with the ripening of yesterday.
Then the bright-red raspberries—the darbouses, as we call them
here—beloved by the Blackbird, grow soft and sweet to the palate. The
housewives pluck them and make them into preserves that are not without
merit. As for the shrub itself, when the season for cutting has come,
it is not, despite its beauty, respected by the woodman. It serves,
like any trivial brushwood, in the making of faggots for heating ovens.
Frequently, too, the showy arbutus is ravaged by a caterpillar yet more
to be dreaded than the woodcutter. After this glutton has been at it,
it could not look more desolate had it been scorched and blackened by
fire.
The Moth, a pretty little, snow-white Bombyx, with superb antennary
plumes and a cotton-wool tippet on her thorax, lays her eggs on a leaf
of the arbutus and, in so doing, starts the evil.
You see a little cushion with pointed ends, rather less than an inch in
length; a white eiderdown, tinged with russet, thick, very soft and
formed of hairs fixed with a little gum by the end that points towards
the upper extremity of the leaf. The eggs are sunk in the thickness of
this soft shelter. They possess a metallic sheen and look like so many
nickel granules.
Hatching takes place in September. The first meals are made at the
expense of the native leaf; the later ones at the expense of the leaves
all around. One surface only is nibbled, usually the upper; the other
remains intact, trellised by the network of veins, which are too horny
for the new-born grubs.
The consumption of leaves is effected with scrupulous economy. Instead
of grazing at hazard and using up the pasturage at the dictates of
individual caprice, the flock progresses gradually from the base to the
tip of the leaf, with all heads ranged in a frontal attack, almost in a
straight line. Not a bite is taken beyond this line, until all that
lies on this side of it is eaten up.
As it advances, the flock throws a few threads across the denuded
portion, where nothing remains but the veins and the epidermis of the
opposite surface. Thus is woven a gossamer veil serving as a shelter
from the fierce rays of the sun and as the parachute which is essential
to these weaklings, whom a puff of wind would carry away.
As the result of a more rapid desiccation on the ravaged surface, the
leaf soon begins to curl of its own accord, curving into a gondola
which is covered by a continuous awning stretched from end to end. The
herbage is then exhausted. The flock abandons it and begins again
elsewhere in the near neighbourhood.
After various temporary pastures of this kind, in November, when the
cold weather is at hand, the caterpillars settle permanently at the end
of a bough. Nibbled one by one on their upper surfaces, the leaves of
the terminal bunch draw close to their neighbours, which, excoriated in
their turn, do the same, until the whole forms a bundle, which looks as
if it had been scorched, lashed together with magnificent white silk.
This is the winter habitation, whence the family, still very feeble,
will not issue until the fine weather returns.
The assembling of this leafy framework is not due to any special
industry on the caterpillars’ part; they do not stretch their threads
from leaf to leaf and then, by pulling at these ropes, bring the
various pieces of the structure into contact. It is merely the result
of desiccation on the nibbled surfaces. Fixed cables, it is true,
solidly bind together the leaves brought close to one another by the
contraction due to their aridity; but they do not in any way play the
part of a motive mechanism in the work of the assemblage.
No hauling-ropes are here, no capstans to move the timbers. The feeble
creatures would be incapable of such effort. The thing happens of
itself. Sometimes a floating thread, the plaything of the air, enlaces
some adjacent leaf. This chance footbridge tempts the explorers, who
hasten to strip the accidental prize; and, without other labour, yet
one more leaf bends of its own accord and is added to the enclosure.
For the most part, the house is built by eating; a lodging is procured
by dint of banqueting.
A comfortable house, tightly closed and well-caulked, proof against
rain and snow. We, to guard ourselves against draughts, put sand-bags
against the cracks of our doors and windows; the extravagant little
Arbutus Caterpillar applies pipings of silk-velvet to his shutters.
Things should be cosy inside, however damp the fog. In bad weather, the
rain drips into my house. The leaf-dwelling knows nothing of such
troubles, so true is it that animals often enjoy advantages which
relegate human industry to the second rank.
In this shelter of silk and foliage, the worst three or four months of
the year are passed in a state of complete abstinence. No outings; not
a bite of food. In March, this torpor ceases; and the recluses, those
starving bellies, shift their quarters.
The community now splits up into squads, which spread themselves anyhow
over the adjacent verdure. This is the period of serious devastation.
The caterpillars no longer confine themselves to nibbling one surface
of the leaf; their keen appetites demand the whole of it, down to the
stalk. And now, stage by stage, halt by halt, the arbutus is shorn
bare.
The vagabonds do not return to their winter dwelling, which has become
too closely cramped. They reassemble in groups and weave, here, there
and everywhere, shapeless tents, temporary huts, abandoned for others
as the pasturage round about becomes exhausted. The denuded boughs, to
all seeming ravaged by fire, take on the look of squalid drying-grounds
hung with rags.
In June, having acquired their full growth, the caterpillars leave the
arbutus-tree, descend to earth and spin themselves, amid the dead
leaves, a niggardly cocoon, in which the insect’s hairs to some extent
supplement its silk. A month later, the Bombyx appears.
In his final dimensions, the caterpillar measures nearly an inch and a
quarter in length. His costume does not lack richness or originality: a
black skin with a double row of orange specks on the back; long grey
hairs arranged in bunches; short, snow-white tufts on the sides; and a
couple of brown-velvet protuberances on the first two rings of the
abdomen and also on the last ring but one.
The most remarkable feature, however, consists of two tiny craters,
always open wide; two cunningly fashioned goblets which might have been
wrought from a drop of red sealing-wax. The sixth and seventh segments
of the abdomen are the only ones that bear these vermilion goblets,
placed in the middle of the back. I do not know the function of these
little cups. Perhaps they should be regarded as organs of information,
similar to the Pine Processionary’s dorsal mouths.
The Arbutus Caterpillar is much dreaded in the village. Woodcutters,
faggot-binders, brushwood-gatherers, all are unanimous in reviling him.
They have such a painfully vivid memory of the irritation that, when I
listen to them, I can hardly repress a movement of the shoulders to
relieve the imaginary itching in the middle of my back. I seem to feel
the arbutus-faggot, laden with its glowing rags, rubbing my bare skin.
It is, it appears, a disagreeable job to cut down the shrub alive with
caterpillars during the hottest part of the day and to shake, under the
blows of the axe, that sort of upas-tree, shedding poison in its shade.
As for me, I have no complaint to make of my relations with the ravager
of the arbutus. I have very often handled him; I have applied his fur
to the tips of my fingers, my neck and even my face, for hours at a
time; I have ripped up the nests to extract their populations for the
purpose of my researches; but I have never been inconvenienced. Save in
exceptional circumstances, the approach of the moult perhaps, this
would need a skin less tough than mine.
The thin skin of a child does not enjoy the same immunity, as witness
little Paul, who, having helped me to empty some nests and to collect
the inhabitants with my forceps, was for hours scratching his neck,
which was dotted with red wheals. My ingenuous assistant was proud of
his sufferings in the cause of science, which resulted from
heedlessness and also perhaps from bravado. In twenty-four hours, the
trouble disappeared, without leaving any serious consequences.
All this hardly tallies with the painful experiences of which the
woodcutters talk. Do they exaggerate? That is hardly credible; they are
so unanimous. Then something must have been lacking in my experiments:
the propitious moment apparently, the proper degree of maturity in the
caterpillar, the high temperature which aggravates the poison.
To show itself in its full severity, the urtication demands the
cooperation of certain undefined circumstances; and this cooperation
was wanting. Chance perhaps will one day teach me more than I want to
know; I shall be attacked in the manner familiar to the woodcutters and
shall pass a night in torment, tossing and turning as though on a bed
of live coals.
What the direct contact of the caterpillar did not teach me the
artifices of chemistry will demonstrate with a violence which I was far
from expecting. I treat the caterpillar with ether, just as I treated
the slough of the Pine Processionary. The number of the creatures taken
for the infusion—they are pretty small as yet, are scarcely half the
size which they will attain when mature—is about a hundred. After a
couple of days’ maceration, I filter the liquid and leave it to
evaporate freely. With the few drops that remain I soak a square of
blotting-paper folded in four and apply it to the inner surface of my
fore-arm, with a thin rubber sheet and a bandage. It is an exact
repetition of what I did with the Pine Processionary.
Applied in the morning, the blister hardly takes effect until the
following night. Then by degrees the irritation becomes unendurable;
and the burning sensation is so acute that I am tormented every moment
with the desire to tear off the bandage. However, I hold out, but at
the cost of a sleepless, feverish night.
How well I now understand what the woodcutters tell me! I had less than
a square inch of skin subjected to the torture. What would it be if I
had my back, shoulders, neck, face and arms tormented in this fashion?
I pity you with all my heart, you labourers who are troubled by the
hateful creature.
On the morrow, the infernal paper is removed. The skin is red and
swollen, covered with tiny pimples whence ooze drops of serous fluid.
For five days the itching persists, with a sharp, burning pain, and the
running from the pimples continues. Then the dead skin dries and comes
off in scabs. All is over, save the redness, which is still perceptible
a month later.
The demonstration is accomplished; the Arbutus Caterpillar, capable as
he is of producing, under certain conditions, the same effects which I
obtain by artificial means, fully deserves his odious reputation.